Diurnal 11-ketotestosterone and 17-hydroxyprogesterone saliva profiles in paediatric classical congenital adrenal hyperplasia

OBJECTIVES

The most suitable biochemical markers for therapy adjustment in patients with congenital adrenal hyperplasia are controversial. 11-Oxygenated androgens are a promising new approach. The objective of this study was to investigate the diurnal rhythm of 11-ketotestosterone in children and adolescents in saliva and to correlate it with salivary 17-hydroxyprogesterone.

METHODS

Fifty-one samples of steroid day-profiles from 17 patients were additionally analysed for 11-ketotestosterone, retrospectively. All patients were treated in our university outpatient clinic for paediatric endocrinology between 2020 and 2022. Steroid day-profiles of 17 patients could be examined. The cohort showed a balanced sex ratio. The median age was 13 years. The measurements for 17-hydroxyprogesterone were carried out during routine care by immunoassay. The measurements of 11-ketotestosterone were performed from frozen saliva samples using an implemented in-house protocol for liquid chromatography-tandem mass spectrometry (LC-MS/MS). The most important outcome were the absolute values for 11-ketotestosterone, their diurnal rhythmicity and the correlation with 17-hydroxyprogesterone.

RESULTS

Both steroids show a circadian diurnal rhythm. 17-hydroxyprogesterone and 11-ketotestosterone correlate significantly. 11-Ketotestosterone showed a positive correlation with BMI at all times of the day.

CONCLUSIONS

11-Ketotestosterone shows circadian rhythmicity in our cohort and correlates with 17-hydroxyprogesterone. These findings serve as an important basis for prospective research into 11-oxygenated androgens as therapeutic markers in paediatrics. However, 11-ketotestosterone appears to be very dependent on BMI.

Gonadal androgens are associated with decreased type I interferon production by plasmacytoid dendritic cells and increased IgG titres to BNT162b2 following co-vaccination with live attenuated influenza vaccine in adolescents

mRNA vaccine technologies introduced following the SARS-CoV-2 pandemic have highlighted the need to better understand the interaction of adjuvants and the early innate immune response. Type I interferon (IFN-I) is an integral part of this early innate response that primes several components of the adaptive immune response. Women are widely reported to respond better than men to tri- and quadrivalent influenza vaccines. Plasmacytoid dendritic cells (pDCs) are the primary cell type responsible for IFN-I production, and female pDCs produce more IFN-I than male pDCs since the upstream pattern recognition receptor Toll-like receptor 7 (TLR7) is encoded by X chromosome and is biallelically expressed by up to 30% of female immune cells. Additionally, the TLR7 promoter contains several putative androgen response elements, and androgens have been reported to suppress pDC IFN-I in vitro. Unexpectedly, therefore, we recently observed that male adolescents mount stronger antibody responses to the Pfizer BNT162b2 mRNA vaccine than female adolescents after controlling for natural SARS-CoV-2 infection. We here examined pDC behaviour in this same cohort to determine the impact of IFN-I on anti-spike and anti-receptor-binding domain IgG titres to BNT162b2. Through flow cytometry and least absolute shrinkage and selection operator (LASSO) modelling, we determined that serum-free testosterone was associated with reduced pDC IFN-I, but contrary to the well-described immunosuppressive role for androgens, the most bioactive androgen dihydrotestosterone was associated with increased IgG titres to BNT162b2. Also unexpectedly, we observed that co-vaccination with live attenuated influenza vaccine boosted the magnitude of IgG responses to BNT162b2. Together, these data support a model where systemic IFN-I increases vaccine-mediated immune responses, yet for vaccines with intracellular stages, modulation of the local IFN-I response may alter antigen longevity and consequently improve vaccine-driven immunity.

11-Oxygenated C19 steroids are the predominant androgens responsible for hyperandrogenemia in Cushing's disease

BACKGROUND

Symptoms of hyperandrogenism are common in patients with Cushing's disease (CD), yet they are not sufficiently explained by androgen concentrations. In this study, we analyzed the contribution of 11-oxygenated C19 steroids (11oxC19) to hyperandrogenemia in female patients with CD.

METHODS

We assessed saliva day profiles in females with CD pre (n = 23) and post (n = 13) successful transsphenoidal surgery, 26 female controls, 5 females with CD treated with metyrapone and 5 treated with osilodrostat for cortisol, cortisone, androstenedione (A4), 11-hydroxyandrostenedione (11OHA4), testosterone (TS), 11-ketotestosterone (11KT), as well as metabolites of classic and 11-oxygenated androgens in 24-h urine. In addition, morning baseline levels of gonadotropins and estradiol, sex hormone-binding globulin, cortisol and dehydroepiandrosterone sulfate (DHEAS) in serum and adrenocorticotrophic hormone in plasma in patients and controls were investigated.

RESULTS

Treatment-naïve females with CD showed a significantly elevated area under the curve of 11OHA4 and 11KT in saliva throughout the day compared to controls (11OHA4 mean rank difference (mrd) 18.13, P = 0.0002; 11KT mrd 17.42; P = 0.0005), whereas A4, TS and DHEAS were comparable to controls. Gonadotropin concentrations were normal in all patients with CD. After transsphenoidal surgery, 11oxC19 and their metabolites dropped significantly in saliva (11OHA4 P < 0.0001; 11KT P = 0.0010) and urine (11-oxo-androsterone P = 0.0011; 11-hydroxy-androsterone P < 0.0001), treatment with osilodrostat and metyrapone efficaciously blocked 11oxC19 synthesis.

CONCLUSION

Hyperandrogenemia in CD is predominantly caused by excess of 11oxC19 steroids.

OR27-1 11-Oxygenated C19 Steroids Are the Predominant Androgens Responsible for Hyperandrogenemia in Cushing's Disease

Background

Symptoms of hyperandrogenism are common in patients with Cushing's disease (CD), but they cannot be sufficiently explained by measured concentrations of circulating androgens. In this study we analyzed the contribution of 11-oxygenated (11oxC19) androgens to hyperandrogenemia in female patients with CD as well as the influence of treatment with steroidogenesis inhibitors osilodrostat and metyrapone on 11oxC19 and classic androgens.

Methods

In this single-center study, we assessed saliva day profiles of 23 females with treatment naïve CD, 26 female controls, 5 females with CD treated with metyrapone and 5 treated with osilodrostat for cortisol, cortisone, androstenedione (A4), 11-hydroxyandrostenedione (11OHA4), testosterone (T), 11-ketotestosterone (11KT) by by liquid chromatography tandem mass spectrometry as well as morning baseline levels of gonadotropins and estradiol, sex hormone-binding globulin, cortisol anddehydroepiandrosterone sulfate (DHEAS) in serum and adrenocorticotropic hormone in plasma.

Results

Treatment naïve females with CD showed significantly elevated area under the curve (AUC) of 11OHA4 and 11KT throughout the day compared to controls (11OHA4 mean rank difference (mrd) 18.13, p = 0.0002; 11KT mrd 17.42; p = 0.0005) whereas A4, T and DHEAS were comparable to controls. Patients with more symptoms of hyperandrogenism displayed higher concentrations of 11oxC19 androgens and had significantly lower SHBG concentrations. Gonadotropin levels were normal in all patients with CD (LH 7.18 U/l (SD 14.28 U/l); FSH 7.68 U/l (SD 12.0 U/l)) and did not correlate with any other parameters. Treatment with osilodrostat and metyrapone efficaciously blocked 11oxC19 synthesis. In metyrapone but not in osilodrostat treatment a trend towards increased concentrations of T and significantly increased A4-concentrations were observed (A4 mrd 23.07, p = 0.0119).

Conclusion

Hyperandrogenemia in CD is predominantly caused by excess of 11oxC19 androgens. Due to lower compensatory increase of A4 and T, osilodrostat seems to be more suitable for treatment of females with CD and hyperandrogenism than metyrapone.

Presentation: Tuesday, June 14, 2022 9:45 a.m. - 10:00 a.m.

Mutations in Noncoding Cis-Regulatory Elements Reveal Cancer Driver Cistromes in Luminal Breast Cancer

Whole-genome sequencing of primary breast tumors enabled the identification of cancer driver genes and noncoding cancer driver plexuses from somatic mutations. However, differentiating driver from passenger events among noncoding genetic variants remains a challenge. Herein, we reveal cancer-driver cis-regulatory elements linked to transcription factors previously shown to be involved in development of luminal breast cancers by defining a tumor-enriched catalogue of approximately 100,000 unique cis-regulatory elements from 26 primary luminal estrogen receptor (ER)⁺ progesterone receptor (PR)⁺ breast tumors. Integrating this catalog with somatic mutations from 350 publicly available breast tumor whole genomes, we uncovered cancer driver cistromes, defined as the sum of binding sites for a transcription factor, for ten transcription factors in luminal breast cancer such as FOXA1 and ER, nine of which are essential for growth in breast cancer with four exclusive to the luminal subtype. Collectively, we present a strategy to find cancer driver cistromes relying on quantifying the enrichment of noncoding mutations over cis-regulatory elements concatenated into a functional unit. IMPLICATIONS: Mapping the accessible chromatin of luminal breast cancer led to discovery of an accumulation of mutations within cistromes of transcription factors essential to luminal breast cancer. This demonstrates coopting of regulatory networks to drive cancer and provides a framework to derive insight into the noncoding space of cancer.

Salivary Profiles of 11-oxygenated Androgens Follow a Diurnal Rhythm in Patients With Congenital Adrenal Hyperplasia

CONTEXT

Several studies have highlighted the importance of the 11-oxygenated 19-carbon (11oxC19) adrenal-derived steroids as potential biomarkers for monitoring patients with 21-hydroxylase deficiency (21OHD).

OBJECTIVE

To analyze circadian rhythmicity of 11oxC19 steroids in saliva profiles and evaluate their relevance as potential monitoring parameters in 21OHD.

DESIGN, SETTING, AND PARTICIPANTS

Cross-sectional single-center study including 59 patients with classic 21OHD (men = 30; women = 29) and 49 body mass index- and age-matched controls (men = 19; women = 30).

OUTCOME MEASURES

Salivary concentrations of the following steroids were analyzed by liquid chromatography-tandem mass spectrometry: 17-hydroxyprogesterone (17OHP), androstenedione (A4), testosterone (T), 11β-hydroxyandrostenedione (11OHA4), and 11-ketotestosterone (11KT).

RESULTS

Similar to the previously described rhythmicity of 17OHP, 11OHA4 and 11KT concentrations followed a distinct diurnal rhythm in both patients and controls with highest concentrations in the early morning and declining throughout the day (11-OHA4: mean reduction of hormone concentrations between timepoint 1 and 5 (Δ mean) in male patients = 66%; male controls Δ mean = 83%; female patients Δ mean = 47%; female controls Δ mean = 86%; 11KT: male patients Δ mean = 57%; male controls Δ mean = 63%; female patients Δ mean = 50%; female controls Δ mean = 76%). Significant correlations between the area under the curve for 17OHP and 11KT (rpmale = 0.773<0.0001; rpfemale = 0.737<0.0001), and 11OHA4 (rpmale = 0.6330.0002; rpfemale = 0.5640.0014) were observed in patients but not present or reduced in controls.

CONCLUSIONS

Adrenal 11oxC19 androgens are secreted following a diurnal pattern. This should be considered when evaluating their utility for monitoring treatment control.

11-oxygenated androgens and their relation to hypothalamus-pituitary-gonadal-axis disturbances in adults with congenital adrenal hyperplasia

CONTEXT

Hypothalamus-pituitary-gonadal (HPG)-axis disturbances are a common phenomenon in patients with classic congenital adrenal hyperplasia (CAH). 11-oxygenated androgens have been suggested to play a role in this context.

DESIGN

Cross-sectional single center study including 89 patients (N = 42 men, N = 55 women) with classic CAH.

MAIN OUTCOME MEASURES

Differences in steroid markers in men with hypogonadism and women with secondary amenorrhea with a special focus on 11-ketotestosterone (11KT) and 11β-hydroxyandrostenedione (11OHA4).

RESULTS

Hypogonadotropic hypogonadism was present in 23 % of men and 61 % of those women currently not on contraceptives suffered from irregular menstrual cycles or amenorrhea. Testicular adrenal rest tumor (TART) was documented in 28 % of men. 11KT (3.5x) and 11OHA4 (5.7x) among other adrenal steroids were significantly elevated in men with hypogonadism and in women with amenorrhea in comparison to those with a regular cycle (11KT: 5.2x; 11OHA4: 3.7x). 11-oxygenated androgens were not higher in men with TART than in those without. There was a negative association of 11KT and 11OHA4 with FSH but not with LH in men. As expected, all steroids were strongly correlated with each other and cases of disproportionally elevated 11-oxygenated androgens that could explain for HPG-disturbances or TART in otherwise controlled patients were rare and also found in eugonadal individuals.

CONCLUSIONS

In CAH, 11-oxygenated androgens are elevated in women with menstrual disturbances and in men with hypogonadotropic hypogonadism. Due to the close correlation of 11-oxygenated androgens with other adrenal steroids it remains to be shown if their measurement is superior to conventional markers of androgen control.

Steroid Ligands, the Forgotten Triggers of Nuclear Receptor Action; Implications for Acquired Resistance to Endocrine Therapy

PURPOSE

There is strong epidemiologic evidence indicating that estrogens may not be the sole steroid drivers of breast cancer. We hypothesize that abundant adrenal androgenic steroid precursors, acting via the androgen receptor (AR), promote an endocrine-resistant breast cancer phenotype.

EXPERIMENTAL DESIGN

AR was evaluated in a primary breast cancer tissue microarray (n = 844). Androstenedione (4AD) levels were evaluated in serum samples (n = 42) from hormone receptor-positive, postmenopausal breast cancer. Levels of androgens, progesterone, and estradiol were quantified using LC/MS-MS in serum from age- and grade-matched recurrent and nonrecurrent patients (n = 6) before and after aromatase inhibitor (AI) therapy (>12 months). AR and estrogen receptor (ER) signaling pathway activities were analyzed in two independent AI-treated cohorts.

RESULTS

AR protein expression was associated with favorable progression-free survival in the total population (Wilcoxon, P < 0.001). Pretherapy serum samples from breast cancer patients showed decreasing levels of 4AD with age only in the nonrecurrent group (P < 0.05). LC/MS-MS analysis of an AI-sensitive and AI-resistant cohort demonstrated the ability to detect altered levels of steroids in serum of patients before and after AI therapy. Transcriptional analysis showed an increased ratio of AR:ER signaling pathway activities in patients failing AI therapy (t test P < 0.05); furthermore, 4AD mediated gene changes associated with acquired AI resistance.

CONCLUSIONS

This study highlights the importance of examining the therapeutic consequences of the steroid microenvironment and demonstrable receptor activation using indicative gene expression signatures.

Patient Response to Receiving a Notification of Elevated Breast Cancer Risk after Regular Screening Mammogram

Background: Population-based screening for breast cancer risk can identify unaffected women at elevated risk and inform them of risk-management options. The James Cancer Hospital recently began assessing risk for women undergoing routine screening mammography. Women found to have ≥20% lifetime risk are notified – with their mammogram results via mail and electronic medical record – that they may be at elevated risk of breast cancer and should consider consulting a high-risk provider. This initial study examined findings from a subsample who participated 2–6 weeks post-notification. Purpose: We sought to determine whether women noticed and understood the notification, and to examine their reactions to the notification of elevated risk. Methods: Of 415 women recruited, 150 (36%) completed the survey, which included items to assess memory and comprehension of the notification, and whether participants had (a) seen a healthcare provider since the notification, and (b) discussed breast cancer risk and management options during that appointment. Results: Participants (aged 40–69; mean = 50.8 years) were mostly White (86%), well-educated (77%), and with above-average income (65%). Most remembered receiving the notification (73%), perceived the information not to be complex (73%), and were confident they understood the notification (93%). Somewhat fewer (64%) remembered that the notification indicated they may be at elevated risk for breast cancer, and 44% also recalled the suggestion to meet with a healthcare provider about this risk. Of the 28 participants who had already seen any healthcare provider in the few weeks since the notification, 50% discussed breast cancer risk during that appointment and 25% said they did so because of the notification. Discussions included family cancer history, actual risk of developing breast cancer, and options for additional imaging or testing. Conclusions: These findings indicate that population-based screening associated with routine mammography can motivate women at elevated breast cancer risk to discuss their risk and management options with a healthcare provider. For some proportion of women, however, complementary communication strategies may also be needed to ensure they gain awareness of their higher-risk status.

Intracrine Testosterone Activation in Human Pancreatic β-Cells Stimulates Insulin Secretion

Testosterone (T) affects β-cell function in men and women. T is a prohormone that undergoes intracrine conversion in target tissues to the potent androgen dihydrotestosterone (DHT) via the enzyme 5α-reductase (5α-R) or to the active estrogen 17β-estradiol (E2) via the aromatase enzyme. Using male and female human pancreas sections, we show that the 5α-R type 1 isoform (SRD5A1) and aromatase are expressed in male and female β-cells. We show that cultured male and female human islets exposed to T produce DHT and downstream metabolites. In these islets, exposure to the 5α-R inhibitors finasteride and dutasteride inhibited T conversion into DHT. We did not detect T conversion into E2 from female islets. However, we detected T conversion into E2 in islets from two out of four male donors. In these donors, exposure to the aromatase inhibitor anastrozole inhibited E2 production. Notably, in cultured male and female islets, T enhanced glucose-stimulated insulin secretion (GSIS). In these islets, exposure to 5α-R inhibitors or the aromatase inhibitor both inhibited T enhancement of GSIS. In conclusion, male and female human islets convert T into DHT and E2 via the intracrine activities of SRD5A1 and aromatase. This process is necessary for T enhancement of GSIS.

SUN-208 The Intra-Individual Variability of 11-Ketotestosterone and 11β-Hydroxyandrostenedione

Background

Emerging evidence has suggested the 11-oxygenated steroids may be important in the diagnosis and monitoring of hyperandrogenism. Two in particular, 11-ketotestosterone (11KT) and 11β-hydroxyandrostenedione (11OHA4) have been implicated in polycystic ovary syndrome, congenital adrenal hyperplasia, precocious puberty and castration resistant prostate cancer. Despite the interest in these analytes, some of their more fundamental properties have yet to be determined. At present, no data is available that quantifies the biological variation of 11KT and 11OHA4 within individuals over time, this may be important as we look to establish normative reference ranges for these potentially useful analytes.

Objective

Here we sought to define the intra-individual variability of 11KT and 11OHA4 in serum using LC-MS/MS.

Method

Blood was collected from 18 healthy volunteers (8 males, 10 females) on the same day each week over a 10 week period using standard venepuncture technique. After collection, the samples were centrifuged within 1 hour, aliquoted and stored at -20°C (-4°F) prior to analysis. All samples from individual volunteers were analysed by LC-MS/MS in triplicate within the same batch so as to limit analytical variability.

Results

The mean analytical coefficient of variation (CV%) for the triplicate analysis was 3.2% for 11KT and 3.7% for 11OHA4. No significant difference was observed between the variability of 11KT concentrations in the male and female cohorts; total intra-individual variation for 11KT was 18.0%. Concentrations of 11OHA4 were more variable in the male cohort when compared to the female cohort. This was reflected by differences in their respective intra-individual variations of 32.5% vs 24.8%.

Summary

Intra-individual variation is an important consideration when interpreting patient results. Concentrations of 11KT were tightly regulated in both the male and female cohorts with no clear demarcation between the two groups. Although concentrations of 11OHA4 were prone to greater variation over the 10 week period, considerable overlap was observed between the male and female subjects. Our data suggests that 11KT and 11OHA4 concentrations are not significantly affected by the menstrual cycle.

Measurement of Salivary Adrenal-Specific Androgens as Biomarkers of Therapy Control in 21-Hydroxylase Deficiency

BACKGROUND

Monitoring of hormonal control represents a key part of the management of congenital adrenal hyperplasia (CAH). Monitoring strategies remain suboptimal because they rely on frequent blood tests and are not specific for adrenal-derived hormones. Recent evidence suggests the crucial role of adrenal-specific 11-oxygenated-C19 androgens in the pathogenesis of CAH.

OBJECTIVE

To establish a correlation between plasma and salivary adrenal-specific androgens in CAH as a noninvasive monitoring strategy.

DESIGN

This prospective cross-sectional study recruited patients between 2015 and 2018.

SETTING

Multicenter study including 13 tertiary centers in the United Kingdom.

PARTICIPANTS

Seventy-eight children with CAH and 62 matched healthy controls.

METHODS

Using liquid chromatography-tandem mass spectrometry, plasma and salivary concentrations of five steroids were measured: 17-hydroxyprogesterone (17OHP), androstenedione (A4), testosterone (T), 11-hydroxyandrostenedione (11OHA4), and 11-ketotestosterone (11KT). The correlation between plasma and salivary steroids was analyzed to assess their use in clinical practice.

RESULTS

Strong correlations between plasma and salivary steroid concentrations in patients with CAH were detected: 17OHP (rs = 0.871; P < 0.001), A4 (rs = 0.931; P < 0.001), T (rs = 0.867; P < 0.001), 11OH4A (rs = 0.876; P < 0.001), and 11KT (rs = 0.944; P < 0.001). These results were consistent for patient subgroups based on sex and age. Analysis of patient subgroups based on 17OHP concentrations established clear correlations between plasma and salivary concentrations of the adrenal-specific androgen 11KT.

CONCLUSIONS

The current study identified tight correlations between plasma and saliva for the adrenal-derived 11-oxygenated C19 androgen 11KT, as well as 17OHP and A4, which are widely used for monitoring treatment in CAH. This combination of steroid hormones will serve as an improved noninvasive salivary test for disease monitoring in patients with CAH.

SAT-004 The Development And Application Of An Lc-ms/ms Method To Investigate The Stability Of 11β-hydroxyandrostenedione And 11-ketotestosterone

Background Recent evidence suggests that 11-oxygenated C19 steroids may have an important role in the assessment of hyperandrogenism [1]. Two in particular, 11β-hydroxyandrostenedione (11OHA4) and 11-ketotestosterone (11KT) have been implicated in polycystic ovarian syndrome [2] and congenital adrenal hyperplasia [3]. At present there are limited methods available to quantitate these potentially useful analytes and no data is available on their stability. Objectives Here, we sought to develop an LC-MS/MS assay to quantify total serum testosterone (T), androstenedione (A4), 17-hydroxyprogesterone (17OHP), 11OHA4 and 11KT. In addition, we aimed to apply the method to evaluate the stability of 11OHA4 and 11KT. Method An LC-MS/MS assay that measured total serum T, A4, 17OHP, 11OHA4 and 11KT was developed and validated in accordance with FDA guidelines. The method was applied to assess the stability of each analyte in serum over a 3 day period. Seven BD Vacutainer® SST™ tubes were collected from 14 volunteers (6 males, 8 females) into. The tubes were stored unseparated at 20°C (68°F) and retrieved at the following times points: 0, 2, 8, 12, 24, 48 and 72h. Once retrieved, samples were centrifuged, aliquoted and stored at -20°C (-4°F) prior to analysis. Results The performance characteristics of the method were acceptable when assessed against an industry standard. Although 11OHA4 concentrations did not significantly change over the 3 day period, we observed a progressive and statistically significant increase in 11KT concentrations between day 0 to day 3 (p<0.001). This increase was most pronounced between time 0 and 8h with concentrations rising on average 26% (95% CI 18 – 33). Summary We have developed a robust LC-MS/MS assay to quantify T, A4, 17OHP, 11OHA4 and 11KT. Application of the method to assess stability has shown that 11KT concentrations increase in-vitro. This change is likely to be clinically significant and underpins the necessity to standardise sample collection before conclusions can be made about the clinical utility of 11KT. References [1] Pretorius E, Arlt W, Storbeck KH. A new dawn for androgens: Novel lessons from 11-oxygenated C19 steroids. Mol Cell Endocrinol. 2017;441:76-85. [2] O’Reilly MW, Kempegowda P, Jenkinson C, Taylor AE, Quanson JL, Storbeck KH, Arlt W. 11-Oxygenated C19 steroids are the predominant androgens in polycystic ovary syndrome. J Clin Endocrinol Metab. 2017;102:2016-3285. [3] Turcu AF, Nanba AT, Chomic R, Upadhyay SK, Giordano TJ, Shields JJ, Merke DP, Rainey WE, Auchus RJ. Adrenal-derived 11-oxygenated 19-carbon steroids are the dominant androgens in classic 21-hydroxylase deficiency. Eur J Endocrinol. 2016;174:601-609.

BILL E. KUNKLE INTERDISCIPLINARY BEEF SYMPOSIUM: A meta-analysis of research efforts aimed at reducing the impact of fescue toxicosis on cattle weight gain and feed intake

The objective of this paper is to present a systematic review and meta-analysis of research efforts aimed at recovering cattle production losses attributed to toxic endophyte-infected [ (Morgan-Jones & Gams.) Glenn, Bacon, & Hanlin comb. Nov.] tall fescue [ (Schreb.) Darbysh.]. The strategies presented include those 1) applied with forage systems, 2) based on pharmacological compounds and functional foods, and 3) based on supplemental dietary nutrients. Cattle BW gain and DM intake was the dependent response evaluated. Among the forage systems reviewed, studies with nontoxic, endophyte-infected tall fescue as a total replacement forage system demonstrated the greatest improvement in per-hectare (152 ± 27.5 kg/ha) and per-animal (0.29 ± 0.03 kg/d) BW gain. Studies with interseeded legumes have exhibited a small and highly variable BW gain effect size per hectare (52 ± 24.1 kg/ha) and per animal (0.11 ± 0.03 kg/d). The legume response was seasonal, with summer exhibiting the greatest benefit. Studies with chemicals that suppress plant growth demonstrated BW gain responses (0.17 ± 0.06 kg/d) equal to or greater than the response observed with legume studies. Cattle grazing toxic tall fescue responded well to anthelmentics, antimicrobial feed additives, and steroid implants, and the use of these technologies may additively help recover production losses. As a group, functional foods have not improved BW gain ( = 0.85). Studies with cattle supplemented with highly digestible fiber supplements observed a 0.15 kg greater BW gain compared with studies using starch- and sugar-based supplements ( < 0.05). Weight gain was positively impacted by the level of supplementation (0.06 kg/DM intake as percent BW). Supplement feed conversion was estimated at 6:1 for the highly digestible fiber supplements compared with 11:1 for starch-based supplements. Tall fescue forage DM intake was predicted to maximize at a supplemental feeding rate of 0.24% BW with a breakpoint at 0.5% BW, and total maximum DM intake (forage plus supplement) occurred at 2.7% BW when supplemental feeding approached 0.9% BW. Results from this meta-analysis should be useful for 1) establishing and comparing measured responses to theoretical improvements in BW gain when additive strategies are considered, 2) research planning, and 3) producer education.

Spatial genomic heterogeneity within localized, multifocal prostate cancer

Herein we provide a detailed molecular analysis of the spatial heterogeneity of clinically localized, multifocal prostate cancer to delineate new oncogenes or tumor suppressors. We initially determined the copy number aberration (CNA) profiles of 74 patients with index tumors of Gleason score 7. Of these, 5 patients were subjected to whole-genome sequencing using DNA quantities achievable in diagnostic biopsies, with detailed spatial sampling of 23 distinct tumor regions to assess intraprostatic heterogeneity in focal genomics. Multifocal tumors are highly heterogeneous for single-nucleotide variants (SNVs), CNAs and genomic rearrangements. We identified and validated a new recurrent amplification of MYCL, which is associated with TP53 deletion and unique profiles of DNA damage and transcriptional dysregulation. Moreover, we demonstrate divergent tumor evolution in multifocal cancer and, in some cases, tumors of independent clonal origin. These data represent the first systematic relation of intraprostatic genomic heterogeneity to predicted clinical outcome and inform the development of novel biomarkers that reflect individual prognosis.

Pharmacogenetic characterization of indacaterol, a novel beta 2-adrenoceptor agonist

BACKGROUND AND PURPOSE

Indacaterol is a novel beta(2)-adrenoceptor agonist in development for the treatment of chronic obstructive pulmonary disease. The aim of this study was to investigate the comparative pharmacology of indacaterol in recombinant cells expressing the common polymorphic variants of the human beta(2)-adrenoceptor and in human primary airway smooth muscle (ASM) cells.

EXPERIMENTAL APPROACH

Chinese hamster ovarian-K1 cell lines expressing high and low levels of the common human beta(2)-adrenoceptor variants were generated [Gly16-Glu27-Val34-Thr164(GEVT), RQVT, GQVT] and also the rare GQVI variant. Human primary ASM cells were isolated from explants of trachealis muscle. Adenosine-3',5'-cyclic-monophosphate production was used as an outcome measure.

KEY RESULTS

In both the low- and high-expression recombinant GEVT 'wild type' cell lines indacaterol is a high-efficacy agonist. Salmeterol and formoterol were identified as low- and high-efficacy agonists, respectively, and showed similar potencies to indacaterol irrespective of the beta(2)-adrenoceptor genotype. The I164 variant cell line was associated with a reduced capacity to generate adenosine-3',5'-cyclic-monophosphate in response to beta(2)-adrenoceptor agonist. In the human primary ASM cells indacaterol gave a maximal response intermediate between that of salmeterol and formoterol.

CONCLUSIONS AND IMPLICATIONS

These data demonstrate that indacaterol is a high-efficacy agonist in recombinant cell systems but acts with lower efficacy in human primary ASM cells. No marked genotype-dependent effects were observed for common variants; however, changes in I164 receptor activity were identified, which were dependent on the level of expression of beta(2)-adrenoceptors.

Endurance training of trained athletes-an electromyogram study

Little is known about the mechanism that improves the capabilities of athletes by high, intensity interval training (HIT). This study was conducted to determine the neurophysiological changes due to HIT. Changes in surface electromyography (SEMG) in well-trained endurance cyclists due to the training were identified. Seven subjects (maximal oxygen uptake [VO2max] 64.6 &#177;4.8 ml.kg-1.min-1, mean &#177; SD) undertook a 3 week training intervention, replacing &#8764; 15% of their weekly endurance training with 6 sessions of laboratory-based HIT (8 &#215; 5 min work bouts at 82% of PPO [&#8764;85% VO2max], with 60 sec active recovery at 100 W). SEMG was used to assess neuromuscular changes before and after the 3 wk training program. During the first and sixth training session, SEMG was recorded. To determine the effects of the HIT program on performance, subjects performed a 40 km time trial (TT40) before and after the training intervention. The frequency of SEMG is a measure of the muscle fatigue and hence was used to identify the variation of the signal properties. Three weeks of intensified training decreased the mean power frequency of the SEMG signal during the latter stages of HIT (interval seven) 50.2 &#177; 5.1 to 47.5 &#177; 4.2 Hz (P < 0.05). The preliminary conclusions of these experiments suggest that high-intensity interval training enhanced endurance performance and reduced the fatiguing of the muscles. It is suggested that this was possibly due to recruitment of addition slow-twitch motor units.

Strategies to identify changes in SEMG due to muscle fatigue during cycling

Detection, quantification and analysis of muscle fatigue is crucial in occupational/rehabilitation and sporting settings. Sports organizations such as Australian Institute of Sports (AIS) currently monitor fatigue by a battery of tests including invasive techniques that require taking blood samples and/or muscle biopsies, the latter of which is highly invasive, painful, time consuming and expensive. SEMG is non-invasive monitoring of the muscle activation and is an indication of localized muscle fatigue based on the observed shift of the power spectral density of the SEMG. But the success of SEMG based techniques is currently limited to isometric contraction and is not acceptable to the human movement community. This paper proposes and tests a simple signal processing technique to identify the onset of muscle fatigue during cyclic activities of muscles such as VL and VM during cycling. Based on experiments conducted with 7 participants, using power output as a measure of fatigue, the technique is able to identify the muscle fatigue with 98% significance.

Assessment of insecticide resistance after the outbreak of diamondback moth (Lepidoptera: Plutellidae) in California in 1997

During an outbreak of the diamondback moth, Plutella xylostella (L.), in California in 1997, nine populations were collected from the major broccoli areas throughout the state. Populations were assayed for their susceptibility to currently used materials (Bacillus thuringiensis subsp. kurstaki, permethrin, and methomyl) and to newer materials that had not yet been commercially used in California (spinosad, emamectin benzoate, and chlorfenapyr). For the currently used insecticides, elevated levels of resistance were seen only with permethrin and seven of the nine populations had tolerance ratios (TR) of > 100. With the newer chemistries, TR values were all < 15. To compare potential cross-tolerance, TR values of the currently used insecticides were compared with TR values of the newer insecticides. There were significant relationships found between: methomyl and emamectin benzoate, methomyl and spinosad, and permethrin and spinosad. Further biochemical studies are needed to confirm the actual mechanisms that lead to these relationships and field tests are needed to determine what impact, if any, such TR levels would have on control in the field. These data indicate that resistance to at least one of the commonly used insecticides (permethrin) may have played a role in the outbreak during 1997. However, other factors may have been at least equally important. The winter of 1996-1997 was warmer than normal, and during the period from February through August of 1997 the amount of rainfall was < 50% of normal. Hot and dry conditions are known to be conducive to outbreaks of P. xylostella. These data add to an overall knowledge about the geographic variation of resistance in P. xylostella populations within the United States. They also serve as a baseline for monitoring changes in susceptibility to these newer insecticides and can also help explain the occurrence of outbreaks caused by factors other than insecticide resistance.

Regulation of IgM and IgD heavy chain gene expression: effect of abrogation of intergenic transcriptional termination

Early IgM+ B cells express little or no membrane IgD due to the low abundance of delta mRNA. Extensive transcriptional termination regulated by sequences in the intronic region between mu and delta heavy chain genes may be the primary reason for the lack of delta gene transcription. We have examined the effect of deletion of these sequences on the regulation of IgM and IgD heavy chain gene expression in transfectants as well as mice carrying this otherwise intact transgene. By run-on transcriptional measurement, we show that the delta exons are transcribed in bone marrow B cells from these transgenic mice. However, in spite of the induced premature synthesis of the full-length mu-delta transcript in pre-B cells, processing to delta mRNA does not occur until the lymphocytes express cell surface IgM. Therefore, during B cell development, synthesis of the full-length transcript is a necessary but not sufficient condition for initiation of delta mRNA synthesis. Furthermore, unexpectedly, the abrogation of transcriptional termination was found to also affect the processing of the primary transcript to microM mRNA. These results show that expression of IgD in primary B cells is stringently regulated and closely linked to IgM expression.

Regulation of IgM and IgD heavy chain gene expression: effect of abrogation of intergenic transcriptional termination

Early IgM+ B cells express little or no membrane IgD due to the low abundance of delta mRNA. Extensive transcriptional termination regulated by sequences in the intronic region between mu and delta heavy chain genes may be the primary reason for the lack of delta gene transcription. We have examined the effect of deletion of these sequences on the regulation of IgM and IgD heavy chain gene expression in transfectants as well as mice carrying this otherwise intact transgene. By run-on transcriptional measurement, we show that the delta exons are transcribed in bone marrow B cells from these transgenic mice. However, in spite of the induced premature synthesis of the full-length mu-delta transcript in pre-B cells, processing to delta mRNA does not occur until the lymphocytes express cell surface IgM. Therefore, during B cell development, synthesis of the full-length transcript is a necessary but not sufficient condition for initiation of delta mRNA synthesis. Furthermore, unexpectedly, the abrogation of transcriptional termination was found to also affect the processing of the primary transcript to microM mRNA. These results show that expression of IgD in primary B cells is stringently regulated and closely linked to IgM expression.

Pregnancies following high-dose cyclophosphamide with or without high-dose busulfan or total-body irradiation and bone marrow transplantation

Patients successfully treated with a marrow transplant often have concerns about fertility and pregnancy. This study was performed to determine pregnancy outcome among patients who had received high-dose chemotherapy alone or with total-body irradiation (TBI) and marrow transplantation for aplastic anemia or hematologic malignancy. Records of 1,326 postpubertal and 196 prepubertal patients currently more than 12 years of age after marrow transplant in Seattle from August 1971 to January 1992 were reviewed to determine the patients with normal gonadal function and pregnancies. Among 708 postpubertal women, 110 recovered normal ovarian function and 32 became pregnant. In addition, nine formerly prepubertal girls with normal gonadal function became pregnant. Among 618 postpubertal men, 157 recovered testicular function and partners of 33 became pregnant. An additional two formerly prepubertal men had partners who became pregnant. Forty-one female patients and partners of 35 male patients had 146 pregnancies after transplant. All 76 patients responded to a questionnaire requesting pregnancy history, outcome, infant birth weight, and congenital anomalies information for all clinically recognized pregnancies. There were 115 live births among 146 (79%) pregnancies. Spontaneous abortion terminated four of 56 (7%) pregnancies for 28 female cyclophosphamide (CY) recipients and six of 16 (37%) pregnancies for 13 TBI recipients (P = .02). Partners of 28 male CY recipients had four of 62 (6.4%) pregnancies terminate with spontaneous abortion, but there were no spontaneous abortions among eight pregnancies of five TBI recipients' partners. Preterm delivery occurred for eight of 44 (18%) and five of eight (63%) live births for 24 CY and eight TBI female recipients (P = .01). This 25% incidence among all female patient pregnancies is higher than the expected incidence of 8% to 10% (P = .0001). The 13 preterm deliveries resulted in 10 low birth weight ([LBW] 1.8 to 2.24 kg) and three very low birth weight ([VLBW] < or = 1.36 kg) infants, for an overall incidence of 25%, which is higher than the expected incidence of 6.5% for the general population (P = .0001). Twelve of the 13 premature infants survive. Congenital anomalies were seen among two of 52 (3.8%) live-born infants of female and six of 63 (9.5%) live-born infants of male patients, which is not different from the 13% of single congenital anomalies reported for the general population. These data demonstrate that clinically recognized pregnancies among women who have received a marrow transplant incorporating TBI are likely to be accompanied by an increased risk of spontaneous abortion. Pregnancies among all women who received a marrow transplant are likely to be accompanied by preterm labor and delivery of LBW or VLBW babies who do not seem to be at an increased risk of congenital anomalies. However, determination of possible adverse effects of parental exposure to high-dose alkylating agents with or without TBI on children born posttransplant requires longer, additional follow-up.

A randomized trial of two preparations of vaginal prostaglandin for pre-induction cervical ripening

OBJECTIVE

To compare two prostaglandin (PG) E2 preparations for pre-induction cervical ripening in a randomized clinical trial.

METHODS

Two milligrams of vaginal PGE2 gel was compared with a vaginal PGE2 3-mg tablet in 200 nulliparous women. Outcomes assessed were induction failure, need for labor augmentation, pain relief requirements, fetal heart rate (FHR) abnormalities, operative delivery rate, induction-to-delivery interval, neonatal condition, and occurrence of uterine hyperstimulation.

RESULTS

There was no statistical difference in pre- and post-dose cervical scores. Compared with the tablet group, women in the gel group were more likely to have significant FHR abnormalities in early labor (odds ratio [OR] 4.77, 95% confidence interval [CI] 1.15-19.5) requiring cesarean delivery. Fetal heart rate tracings in the active phase of labor were also more likely to be abnormal in the gel group (chi 2 = 4.31, P < .05). Compared with the gel group, women in the tablet group were significantly more likely to require operative delivery for poor progress in labor (OR 2.83, 95% CI 1.20-7.24). Other clinical outcomes were identical, with no significant differences in the overall rate of failed induction, cesarean delivery, rate of assisted delivery, requirement for oxytocin infusion, induction-to-delivery interval, pain relief requirements, or neonatal condition.

CONCLUSIONS

When compared with the PGE2 tablet, the use of PGE2 gel for cervical ripening and labor induction in nulliparous women did not result in significant improvements in labor outcome. Whereas the gel was associated with an increase in significant FHR abnormalities, the tablet was associated with an increase in the rate of operative delivery for poor progress in labor.

Role of the OCTA site in regulation of IgH chain gene transcription during B cell activation

We have evaluated the importance of the OCTA site in both the promoter and enhancer regions for the induction of enhancement of IgH chain gene transcription after B cell activation. These studies show that although occupancy of the OCTA site in the promoter is critical for basal transcription of the mu gene, it is not necessary for the increase in transcription induced by in vivo activation. On the other hand, the OCTA site in the enhancer is necessary for neither basal transcription nor in vivo activation of transcription; however, occupancy of this site is required for further up-regulation in transcription of the mu gene in pre-activated cells. These results indicate that different mechanisms may be involved in the activation of resting versus in vivo stimulated B lymphocytes. The findings are discussed in relation to the phenotype described for Oct-2-deficient mice.

Distribution of receptors mediating phosphoinositide hydrolysis in cultured human umbilical artery smooth muscle and endothelial cells

Cultures of human umbilical artery smooth muscle and endothelial cells have been established and the effect of a range of calcium-mobilizing receptor agonists on inositol phospholipid hydrolysis has been compared in the two cell types. In human umbilical artery endothelial cells, histamine (EC50 20 microM), ATP (EC50 6.7 microM), sodium fluoride (20 mM) and thrombin (1 U/mL) produced marked increases in [3H]inositol phosphate accumulation. In contrast, bradykinin (1 microM), 5-hydroxytryptamine (5-HT) (0.1 mM) and carbachol (1 mM) produced only a small (< 1% of the response to 1 mM histamine) effect on [3H]inositol phosphate accumulation in these cells. In human umbilical artery smooth muscle cells, histamine (EC50 16 microM), bradykinin (EC50 4.5 nM), 5-HT (EC50 0.7 microM) and carbachol (EC50 21 microM) produced substantial effects (> 20% of the response to 1 mM histamine) on inositol phospholipid hydrolysis while ATP (1 mM) and thrombin (1 U/mL) were much less effective. The response to histamine in both smooth muscle and endothelial cells was antagonized by 50 nM mepyramine (apparent Kd = 5.6 and 2.9 nM in the two cell types, respectively). The response to 5-HT in smooth muscle cells was antagonized by 50 nM ketanserin (apparent Kd = 4.5 nM). In human umbilical artery smooth muscle cells the inositol phosphate response to carbachol was antagonized by 4-diphenylacetoxy-N-methylpiperidine (4-DAMP; pKd = 9.3), atropine (pKd = 9.7), pirenzepine (pKd = 6.7) and methoctramine (pKd = 6.9). These data are consistent with the involvement of an M3-muscarinic receptor in this response. These studies suggest that receptors mediating inositol phospholipid hydrolysis are differentially distributed between human umbilical artery endothelial and smooth muscle cells.

Role of differential mRNA stability in the regulated expression of IgM and IgD

The expression of IgM and IgD heavy chain mRNA in resting vs activated B cells offers a unique tool for the assessment of the effect of translation on mRNA stability because mu and delta mRNA have identical VDJ sequences but differ substantially in the rest of the molecule. We have shown that despite the 5' UTR identity that allows equal access to the translation machinery, mu mRNA has a significantly higher turnover rate than delta mRNA. However, the short t1/2 of mu mRNA increases significantly after B cell activation. Furthermore, the induction of microS mRNA after B cell activation provides yet another related molecule for comparison. Thus, despite the fact that microS and microM mRNA differ at their 3' ends, they have identical turnover rates in activated B cells. In addition, because the turnover rates of delta mRNA and beta 2 and GAPDH mRNA remain unchanged, these experiments suggest that B cell activation results in the induction of regulatory factor(s) that target specific sequences within mRNA-mu to confer greater stability. They also argue against a more passive regulation of mRNA stability that is a consequence of alterations in the secretory machinery.

Role of differential mRNA stability in the regulated expression of IgM and IgD

The expression of IgM and IgD heavy chain mRNA in resting vs activated B cells offers a unique tool for the assessment of the effect of translation on mRNA stability because mu and delta mRNA have identical VDJ sequences but differ substantially in the rest of the molecule. We have shown that despite the 5' UTR identity that allows equal access to the translation machinery, mu mRNA has a significantly higher turnover rate than delta mRNA. However, the short t1/2 of mu mRNA increases significantly after B cell activation. Furthermore, the induction of microS mRNA after B cell activation provides yet another related molecule for comparison. Thus, despite the fact that microS and microM mRNA differ at their 3' ends, they have identical turnover rates in activated B cells. In addition, because the turnover rates of delta mRNA and beta 2 and GAPDH mRNA remain unchanged, these experiments suggest that B cell activation results in the induction of regulatory factor(s) that target specific sequences within mRNA-mu to confer greater stability. They also argue against a more passive regulation of mRNA stability that is a consequence of alterations in the secretory machinery.

Bradykinin B2- and 5-hydroxytryptamine (5-HT2)-receptor stimulated increases in intracellular calcium in cultured guinea-pig aortic smooth muscle cells

The effect of 5-hydroxytryptamine (5-HT) and bradykinin on intracellular free calcium concentration ([Ca2+]i) has been studied in cultured guinea-pig aortic smooth muscle cells loaded with the Ca(2+)-sensitive fluorescent dye fura-2. Bradykinin and 5-HT elicited rapid increases in [Ca2+]i with log EC50 values of -7.9 +/- 0.05 M (N = 3) and -6.1 +/- 0.1 M (N = 4), respectively. Both agonists stimulated the release of intracellular calcium (Ca2+ responses still present in the absence of extracellular calcium) and to a lesser extent Ca2+ influx (observed when extracellular calcium was re-applied to cells initially stimulated in nominally Ca(2+)-free buffer containing 0.1 mM EGTA). The B1-receptor antagonist des-Arg9,[Leu8]-bradykinin had no effect on calcium responses elicited 100 nM bradykinin, whereas the B2-receptor antagonist D-Arg[Hyp3,Thi5.8,D-Phe7]-bradykinin (10 microM) inhibited the response to 100 nM bradykinin by 43%. The bradykinin B2-receptor antagonist D-Arg[Hyp3,Thi5.8,D-Phe7]-bradykinin virtually abolished the response to 10 nM bradykinin (IC50 4 microM). No increase in [Ca2+]i was observed with the B1-receptor agonist des-Arg9-bradykinin (300 nM). The response to 5-HT (100 microM) was abolished by the 5-HT2 receptor antagonist ketanserin (IC50 = 2 +/- 0.4 nM; N = 3). These data suggest that in cultured guinea-pig aortic smooth muscle cells bradykinin B2- and 5-HT2-receptor activation stimulates the release of Ca2+ from intracellular stores and Ca2+ influx through Ca2+ entry pathways in the plasma membrane.

Investigation of the bleeding patterns of postmenopausal women treated with Estrapak-50

Diary cards of patients in two similar trials of Estrapak-50 hormone replacement therapy were analysed with regard to the characteristics of progestogen-associated bleeding (PAB) and breakthrough bleeding (BTB). Forty out of 52 patients in Study A and 74 out of 92 patients in Study B had diaries suitable for analysis. One patient in Study A and two patients in Study B who withdrew from treatment did so because of unacceptable bleeding problems. Similar results were obtained from both trials. After 6 months of treatment approximately 90% of patients in study A and approximately 70% of patients in study B had PAB on or before day 11. Twenty-seven percent and 49% in studies A and B, respectively, bled prior to day 8, which in the majority of instances affected one treatment cycle. Duration of PAB varied from 1 to 14 days (median 7 days) and the pattern of bleeding in the second cycle was predictive of bleeding in subsequent cycles. Although over 1/3 of women reported some heavy bleeding days, this usually only affected one treatment cycle, and the majority of bleeding was only spotting or light flow. BTB patterns did not raise suspicions of endometrial pathology. Bleeding patterns were both acceptable to patients and, in as much as the current literature indicates that bleeding patterns can be interpreted, were consistent with adequate progestogenic protection of the endometrium.

High-dose dietary myo-inositol supplementation does not alter the ischaemia phenomenon in human diabetics

Five diabetic patients and 3 non-diabetics were subjected to a dietary supplement of 20 g per day of myo-inositol (40 X the normal ingestion) for 14 days. This amount neither produced toxic side-effects nor changed the peripheral nervefunction expressed by motor conduction velocity or resistance to ischaemia.

A comparison study of dynamic visual acuity between athletes and nonathletes

A comparison study of dynamic visual acuity (DVA) was conducted using samples of nonathletic college students and college baseball players. The experimental population consisted of 17 male baseball players ranging in age from 19-24 years. The control population was made up of 25 male graduate students ranging in age from 23-29 years. Subjects reported the direction of a 20/25 "Landolt C" target exhibiting uniform angular motion produced by a projection system. Angular target velocities between 10 deg/sec and 110 deg/sec with an exposure time of 400 ms were used. The results showed a statistically significant difference between the two groups' DVA. The mean DVA for the baseball players was 82.35 deg/sec and 69.90 deg/sec for the control group.

Calculation of 2,3,7,8-TCDD equivalent concentrations of complex environmental contaminant mixtures

Sufficient toxicological data are now available to permit use of conventional risk assessment techniques to estimate the hazards associated with human exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD). However, many real-world exposures involve complex mixtures of dibenzodioxins, dibenzofurans, and related compounds. Historical approaches to risk assessment on such mixtures have ranged from ignoring all compounds except 2,3,7,8-TCDD itself to assuming that all compounds have potencies equal to 2,3,7,8-TCDD. An alternative approach which uses existing literature data and analytical results to calculate the "2,3,7,8-TCDD equivalent" concentration of a mixture in order to "predict" its biological potency relative to 2,3,7,8-TCDD itself is advanced here. Previously reported in vivo acute and subchronic studies and some recently obtained analytical chemistry data are integrated here to clarify the utility of this important approach and to assess the uncertainties associated with its use. This predictive approach, and various conceptually similar ones, have now found wide applicability to the risk assessment process associated with exposure to complex mixtures of dioxins, dibenzofurans, and related compounds.