Ovarian Primitive Neuroectodermal Tumor: Are You Central or Peripheral?

Primitive neuroectodermal tumors (PNETs) of the ovary are rare, highly aggressive neoplasms with fewer than 100 cases described. PNETs of the ovary can be classified as either peripheral or central types. The peripheral PNETs have small round cells with or without rosette formation, and the central PNETs can be further delineated based on the CNS tumor they morphologically resemble. We present a case of a central type ovarian PNET in a young female presenting with a pelvic mass and elevated serum tumor markers.

Disease-Specific Survival of Type I and Type II Epithelial Ovarian Cancers-Stage Challenges Categorical Assignments of Indolence & Aggressiveness

Epithelial ovarian cancers (EOC) consist of several sub-types based on histology, clinical, molecular and epidemiological features that are termed “histo-types”, which can be categorized into less aggressive Type I and more aggressive Type II malignancies. This investigation evaluated the disease-specific survival (DSS) of women with Type I and II EOC using histo-type, grade, and stage. A total of 47,789 EOC cases were identified in the National Cancer Institute’s Surveillance, Epidemiology, and End Results (SEER) data. Survival analysis and log rank test were performed to identify a 2-tiered classification (grade 1 vs. grade 2 & 3) for serous EOC. DSS of early stage serous EOC for grade 2 was significantly different from grade 3 indicating that a 2-tier classification for serous EOC applied only to late stage. DSS of Type I EOC was much better than Type II. However, DSS was 33–52% lower with late stage Type I than with early stage Type I indicating that Type I ovarian cancers should not be considered indolent. Early stage Type II EOC had much better DSS than late stage Type II stressing that stage has a large role in survival of both Type I and II EOC.

Clinical Factors Associated with Longer Hospital Stay Following Ovarian Cancer Surgery

Background: Ovarian cancer (OC) is the leading cause of death from gynecologic malignancy and is treated with a combination of cytoreductive surgery and platinum-based chemotherapy. Extended length of stay (LOS) after surgery can affect patient morbidity, overall costs, and hospital resource utilization. The primary objective of this study was to identify factors contributing to prolonged LOS for women undergoing surgery for ovarian cancer. Methods: The American College of Surgeons National Surgical Quality Improvement Program (ACS-NSQIP) database was queried to identify women from 2012-2016 who underwent hysterectomy for ovarian, fallopian tube and peritoneal cancer. The primary outcome was LOS >50th percentile. Preoperative and intraoperative variables were examined to determine which were associated with prolonged LOS. Results: From 2012-2016, 1771 women underwent elective abdominal surgery for OC and were entered in the ACS-NSQIP database. The mean and median LOS was 4.6 and 4.0 days (IQR 0-38), respectively. On multivariate analysis, factors associated with prolonged LOS included: American Society of Anesthesiologists (ASA) Classification III (aOR 1.71, 95% CI 1.38-2.13) or IV (aOR 1.88, 95% CI 1.44-2.46), presence of ascites (aOR 1.88, 95% CI 1.44-2.46), older age (aOR 1.23, 95% CI 1.13-1.35), platelet count >400,000/mm3 (aOR 1.74, 95% CI 1.29-2.35), preoperative blood transfusion (aOR 11.00, 95% CI 1.28-94.77), disseminated cancer (aOR 1.28, 95% CI 1.03-1.60), increased length of operation (121-180 min, aOR 1.47, 95% CI 1.13-1.91; >180 min, aOR 2.78, 95% CI 2.13-3.64), and postoperative blood transfusion within 72 h of incision (aOR 2.04, 95% CI 1.59-2.62) (p < 0.05 for all). Conclusions: Longer length of hospital stay following surgery for OC is associated with many patient, disease, and treatment-related factors. The extent of surgery, as evidenced by perioperative blood transfusion and length of surgical procedure, is a factor that can potentially be modified to shorten LOS, improve patient outcomes, and reduce hospital costs.

Ovarian Cancer Incidence Corrected for Oophorectomy

Current reported incidence rates for ovarian cancer may significantly underestimate the true rate because of the inclusion of women in the calculations who are not at risk for ovarian cancer due to prior benign salpingo-oophorectomy (SO). We have considered prior SO to more realistically estimate risk for ovarian cancer. Kentucky Health Claims Data, International Classification of Disease 9 (ICD-9) codes, Current Procedure Terminology (CPT) codes, and Kentucky Behavioral Risk Factor Surveillance System (BRFSS) Data were used to identify women who have undergone SO in Kentucky, and these women were removed from the at-risk pool in order to re-assess incidence rates to more accurately represent ovarian cancer risk. The protective effect of SO on the population was determined on an annual basis for ages 5-80+ using data from the years 2009-2013. The corrected age-adjusted rates of ovarian cancer that considered SO ranged from 33% to 67% higher than age-adjusted rates from the standard population. Correction of incidence rates for ovarian cancer by accounting for women with prior SO gives a better understanding of risk for this disease faced by women. The rates of ovarian cancer were substantially higher when SO was taken into consideration than estimates from the standard population.

Complications from Surgeries Related to Ovarian Cancer Screening

The aim of this study was to evaluate complications of surgical intervention for participants in the Kentucky Ovarian Cancer Screening Program and compare results to those of the Prostate, Lung, Colorectal and Ovarian Cancer Screening trial. A retrospective database review included 657 patients who underwent surgery for a positive screen in the Kentucky Ovarian Cancer Screening Program from 1988–2014. Data were abstracted from operative reports, discharge summaries, and office notes for 406 patients. Another 142 patients with incomplete records were interviewed by phone. Complete information was available for 548 patients. Complications were graded using the Clavien–Dindo (C–D) Classification of Surgical Complications and considered minor if assigned Grade I (any deviation from normal course, minor medications) or Grade II (other pharmacological treatment, blood transfusion). C–D Grade III complications (those requiring surgical, endoscopic, or radiologic intervention) and C–D Grade IV complications (those which are life threatening) were considered “major”. Statistical analysis was performed using SAS 9.4 software. Complications were documented in 54/548 (10%) subjects. For women with malignancy, 17/90 (19%) had complications compared to 37/458 (8%) with benign pathology (p < 0.003). For non-cancer surgery, obesity was associated with increased complications (p = 0.0028). Fifty patients had minor complications classified as C–D Grade II or less. Three of 4 patients with Grade IV complications had malignancy (p < 0.0004). In the Prostate, Lung, Colorectal and Ovarian Cancer Screening trial, 212 women had surgery for ovarian malignancy, and 95 had at least one complication (45%). Of the 1080 women with non-cancer surgery, 163 had at least one complication (15%). Compared to the Prostate, Lung, Colorectal and Ovarian Cancer Screening trial, the Kentucky Ovarian Cancer Screening Program had significantly fewer complications from both cancer and non-cancer surgery (p < 0.0001 and p = 0.002, respectively). Complications resulting from surgery performed as a result of the Kentucky Ovarian Cancer Screening Program were infrequent and significantly fewer than reported in the Prostate, Lung, Colorectal and Ovarian Cancer Screening trial. Complications were mostly minor (93%) and were more common in cancer versus non-cancer surgery.

Prospective validation of an intraoperative algorithm to guide surgical staging in early endometrial cancer

OBJECTIVES

Prospectively validate an intraoperative surgical staging algorithm to stratify patients with early endometrial cancer by risk of lymph node metastasis.

METHODS

Subjects with endometrial cancer clinically confined to the uterus were prospectively enrolled at an academic cancer center between Jan 2012 and Jun 2015. Study participants were stratified intraoperatively into two groups based on risk of nodal involvement using cell type, tumor grade, myometrial invasion, and tumor size in accordance with an established protocol from the Mayo Clinic. Low risk (LR) subjects received extrafascial hysterectomy with bilateral salpingo-oophorectomy; high risk (HR) patients received complete surgical staging including bilateral pelvic and para-aortic lymphadenectomy.

RESULTS

Of the 200 subjects enrolled, 194 were eligible for analysis. The algorithm identified 132 (68%) HR and 62 (32%) LR cancers. Of the HR subjects, 126 had lymphadenectomy performed with 14 (11%) positive for nodal metastases. Five HR subjects experienced disease recurrence. Of the 62 LR cancers, two patients developed disease recurrence. Ten LR cancers were upgraded to HR on final pathology due to lesion size (6) and grade (4). None of these patients experienced disease recurrence. The algorithm demonstrated 90% sensitivity (18/20) and 36% specificity (62/174) as determined by positive lymph nodes and/or disease recurrence.

CONCLUSIONS

Intraoperative assessment of early endometrial cancer can be used to determine the extent of surgical staging. The studied algorithm has low specificity and modifications are necessary to better match the surgical procedure to the risk of metastatic cancer.

Inhibition of the integrin/FAK signaling axis and c-Myc synergistically disrupts ovarian cancer malignancy

Integrins, a family of heterodimeric receptors for extracellular matrix, are promising therapeutic targets for ovarian cancer, particularly high-grade serous-type (HGSOC), as they drive tumor cell attachment, migration, proliferation and survival by activating focal adhesion kinase (FAK)-dependent signaling. Owing to the potential off-target effects of FAK inhibitors, disruption of the integrin signaling axis remains to be a challenge. Here, we tackled this barrier by screening for inhibitors being functionally cooperative with small-molecule VS-6063, a phase II FAK inhibitor. From this screening, JQ1, a potent inhibitor of Myc oncogenic network, emerged as the most robust collaborator. Treatment with a combination of VS-6063 and JQ1 synergistically caused an arrest of tumor cells at the G2/M phase and a decrease in the XIAP-linked cell survival. Our subsequent mechanistic analyses indicate that this functional cooperation was strongly associated with the concomitant disruption of activation or expression of FAK and c-Myc as well as their downstream signaling through the PI3K/Akt pathway. In line with these observations, we detected a strong co-amplification or upregulation at genomic or protein level for FAK and c-Myc in a large portion of primary tumors in the TCGA or a local HGSOC patient cohort. Taken together, our results suggest that the integrin–FAK signaling axis and c-Myc synergistically drive cell proliferation, survival and oncogenic potential in HGSOC. As such, our study provides key genetic, functional and signaling bases for the small-molecule-based co-targeting of these two distinct oncogenic drivers as a new line of targeted therapy against human ovarian cancer.

Effects of Joint Exposures to Selected Peroxisome Proliferators on Hepatic Acyl-CoA Oxidase Activity in Male B6C3F1 Mice

The interaction potential of peroxisome proliferators of similar and dissimilar structure was examined in B6C3F1 mice. Mice were fed diets containing varying concentrations of ciprofibrate (Cipro), clofibrate (Clof) or di(2-ethylhexyl)phthalate (DEHP), or combinations of Cipro and Clof or Cipro and DEHP for 4 d. Induction of peroxisomal beta-oxidation, measured by increased acyl-CoA oxidase activity, was used as the endpoint for analysis. An additive response occurred following joint exposure to the structurally related compounds Cipro and Clof, whereas a possible synergistic response occurred at low dose combinations of the structurally dissimilar Cipro and DEHP. These findings represent the first report assessing the in-vivo interaction potential of structurally similar and dissimilar peroxisome proliferators and provides insight into the dose-response nature of joint exposures to certain non-genotoxic carcinogens.

Probability of fallopian tube and ovarian detection with transvaginal ultrasonography in normal women

Objective: Some ovarian malignancies may originate in the fallopian tube. The feasibility of ultrasonographically visualizing the fallopian tube is presented. Methods: In total, 549 normal women participated in the fallopian tube visualization trial, while ovarian visualization was studied in 43,521. Chi-square analysis, t-tests and multivariate analysis determined significance and interactions. Results: Ovaries were observed in 82.7% while fallopian tubes were detected in 77.2% of women and 85.2% of the time when an ovary was detected. Age, BMI or parity was not significantly different when one or both fallopian tubes were visualized. Elevated BMI had slightly greater influence than age in limiting visualization of the fallopian tubes in multivariate analysis. Conclusion: Fallopian tubes can often be identified sonographically. Ovarian visualization provides the strongest indicator favoring fallopian tube detection. Thus, ultrasonographic examinations for adnexal cancer could include evaluation of fallopian tubes even in women >60 years and in women with BMI ≥25.

CD151-α3β1 integrin complexes suppress ovarian tumor growth by repressing slug-mediated EMT and canonical Wnt signaling

Human ovarian cancer is diagnosed in the late, metastatic stages but the underlying mechanisms remain poorly understood. We report a surprising functional link between CD151-α3β1 integrin complexes and the malignancy of serous-type ovarian cancer. Analyses of clinical specimens indicate that CD151 expression is significantly reduced or diminished in 90% of metastatic lesions, while it remains detectable in 58% of primary tumors. These observations suggest a putative tumor-suppressing role of CD151 in ovarian cancer. Indeed, our analyses show that knocking down CD151 or α3 integrin enhances tumor cell proliferation, growth and ascites production in nude mice. These changes are accompanied by impaired cell-cell contacts and aberrant expression of E-cadherin, Mucin 5AC and fibronectin, largely reminiscent of an epithelial to mesenchymal transition (EMT)-like change. Importantly, Slug, a master regulator of EMT, is markedly elevated. Knocking down Slug partially restores CD151-α3β1 integrin complex-dependent suppression of cell proliferation. Moreover, disruption of these adhesion protein complexes is accompanied by a concomitant activation of canonical Wnt signaling, including elevated levels of β-catenin and Axin-2 as well as resistance to the inhibition in β-catenin-dependent transcriptional complexes. Together, our study demonstrates that CD151-α3β1 integrin complexes regulate ovarian tumor growth by repressing Slug-mediated EMT and Wnt signaling.

CD151 represses mammary gland development by maintaining the niches of progenitor cells

Tetraspanin CD151 interacts with laminin-binding integrins (i.e., α3β1, α6β1 and α6β4) and other cell surface molecules to control diverse cellular and physiological processes, ranging from cell adhesion, migration and survival to tissue architecture and homeostasis. Here, we report a novel role of CD151 in maintaining the branching morphogenesis and activity of progenitor cells during the pubertal development of mammary glands. In contrast to the disruption of laminin-binding integrins, CD151 removal in mice enhanced the tertiary branching in mammary glands by 2.4-fold and the number of terminal end buds (TEBs) by 30%, while having minimal influence on either primary or secondary ductal branching. Consistent with these morphological changes are the skewed distribution of basal/myoepithelial cells and a 3.2-fold increase in proliferating Ki67-positive cells. These novel observations suggest that CD151 impacts the branching morphogenesis of mammary glands by upregulating the activities of bipotent progenitor cells. Indeed, our subsequent analyses indicate that upon CD151 removal the proportion of CD24(Hi)CD49f(Low) progenitor cells in the mammary gland increased by 34%, and their proliferating and differentiating activities were significantly upregulated. Importantly, fibronectin, a pro-branching extracellular matrix (ECM) protein deposited underlying mammary epithelial or progenitor cells, increased by >7.2-fold. Moreover, there was a concomitant increase in the expression and nuclear distribution of Slug, a transcription factor implicated in the maintenance of mammary progenitor cell activities. Taken together, our studies demonstrate that integrin-associated CD151 represses mammary branching morphogenesis by controlling progenitor cell activities, ECM integrity and transcription program.

Abstract A110: Factors affecting cervical cancer survival for patients referred to a tertiary care center in Kentucky

Objectives: The aim of this research was to identify prognostic factors influencing cervical cancer recurrence and survival in Kentucky.

Methods: A cohort study was performed to assess predictive survival factors of cervical cancer patients referred to the University of Kentucky using the University of Kentucky database and the Kentucky Cancer Registry from January 2001 to May 2010. Eligibility criteria include those at least 18 years old, a history of cervical cancer, and no prior history of malignancy. Descriptive statistics were compiled for age, race, insurance status, tobacco use, Appalachian or non-Appalachian residence using the Appalachian Regional Commission classification of county, co-morbid risk factors, BMI, and pathologic characteristics. Univariable and multivariable Cox proportional hazard analysis were performed to assess associations with cervical cancer recurrence and overall survival.

Results: 380 patients met entry criteria. 91 % were Caucasian (N=346), 43% were uninsured (N=163), and 64% (N=242) lived in Appalachia. While 48% (N=184) of the population had no co-morbid risk factors, 41 % (N=156) had one or two risk factors. The following covariates were not associated with recurrence free or overall survival: race, BMI, Appalachian residence, insurance status, months between last normal cervical cytology and diagnosis, histology (squamous cell carcinoma vs. adenocarcinoma vs. other), and tumor grade. The univariable analysis revealed age [HR1.02 (95%CI 1.01,1.04)], having more than two co-morbid risk factors [HR 2.8 (95%CI 1.1, 7.2)], and diagnosis in disease stages II, III, and IV [HR 5.0 (95% 2.3,10.9); 11.0 (5.2,23.1); 43.7 (19.0,100.3)] were associated with a worse recurrence-free survival while age [HR 1.03 (95%CI 1.02,1.04)], having more than two co-morbid risk factors [HR 3.7 (95%CI 1.8, 7.9)], smoking status [HR 1.4 (95%CI 1.0,2.5)], and diagnosis in disease stages II, III, and IV [HR 4.0 (95%CI 2.2, 7.1); 7.3 (95%CI 4.1,12.9); 32.7 (16.8,63.8)] all significantly decreased overall survival. After controlling for all significant variables, Stage IV disease was a significant predictor of progression-free survival [HR 3.6 (95%CI 2.0,6.4)] while stages II, III, and IV [HR 3.0 (95%CI 1.6,5.7); 6.0 (95%CI 3.3,11.0); 38.9 (95%CI 18.0,84.0)] and having more than two co-morbid risk factors [HR 2.3 (95%CI 1.0,5.2)] remained significant adverse predictors for overall survival.

Conclusions: Co-morbid risk factors and stage influence cervical cancer survival. Future cervical carcinoma research should consider medical co-morbidities as an important factor impacting survival.

Citation Information: Cancer Epidemiol Biomarkers Prev 2010;19(10 Suppl):A110.

Defining hormesis

Much confusion surrounds the concept of hormesis and what its biological meaning represents. This paper provides a definition of hormesis that addresses its historical foundations, quantitative features, and underlying evolutionary and toxicologically based mechanistic strategies. Hormesis should be considered an adaptive response characterized by biphasic dose responses of generally similar quantitative features with respect to amplitude and range of the stimulatory response that are either directly induced or the result of compensatory biological processes following an initial disruption in homeostasis. Given the limited magnitude of the stimulatory response (i.e., usually 30-60% greater than controls at maximum), heightened study design and replication requirements are often necessary to ensure reliable judgments on causality. Even though hormesis is considered an adaptive response, the issue of beneficial/harmful effects should not be part of the definition of hormesis, but reserved to a subsequent evaluation of the biological and ecological context of the response.

The effects of gamma rays on longevity

A number of animal model studies have assessed the capacity of long-term whole body gamma rays to affect life span. The initial goal of such studies was to establish the equivalent of a no observed adverse effects level (NOAEL) that would provide a toxicological foundation for deriving an acceptable worker exposure standard. In the course of initial studies to establish such a 'tolerance threshold', data emerged suggesting that low dose rates/cumulative doses enhanced longevity in mice and guinea pigs of both sexes. Extensive large scale follow-up investigations with other mouse strains and rats revealed what appear to be inter-strain/species differences in response with some models providing strong evidence for a low dose increase in longevity. The subsequent positive studies in mouse models were generally well designed, well conducted and used extensive numbers of mice. In all experiments that displayed enhanced longevity the average life span was enhanced by 10-30% but not the maximum life span potential. The underlying mechanisms affecting the apparent enhancement in longevity are believed to result from the stimulation of hematopoietic and immune systems following an initial low level chronic injury to the bone marrow.

The frequency of U-shaped dose responses in the toxicological literature

Hormesis has been defined as a dose-response relationship in which there is a stimulatory response at low doses, but an inhibitory response at high doses, resulting in a U- or inverted U-shaped dose response. To assess the proportion of studies satisfying criteria for evidence of hormesis, a database was created from published toxicological literature using rigorous a priori entry and evaluative criteria. One percent (195 out of 20,285) of the published articles contained 668 dose-response relationships that met the entry criteria. Subsequent application of evaluative criteria revealed that 245 (37% of 668) dose-response relationships from 86 articles (0.4% of 20,285) satisfied requirements for evidence of hormesis. Quantitative evaluation of false-positive and false-negative responses indicated that the data were not very susceptible to such influences. A complementary analysis of all dose responses assessed by hypothesis testing or distributional analyses, where the units of comparison were treatment doses below the NOAEL, revealed that of 1089 doses below the NOAEL, 213 (19.5%) satisfied statistical significance or distributional data evaluative criteria for hormesis, 869 (80%) did not differ from the control, and 7 (0.6%) displayed evidence of false-positive values. The 32.5-fold (19.5% vs 0.6%) greater occurrence of hormetic responses than a response of similar magnitude in the opposite (negative) direction strongly supports the nonrandom nature of hormetic responses. This study, which provides the first documentation of a data-derived frequency of hormetic responses in the toxicologically oriented literature, indicates that when the study design satisfies a priori criteria (i.e., a well-defined NOAEL, > or = 2 doses below the NOAEL, and the end point measured has the capacity to display either stimulatory or inhibitory responses), hormesis is frequently encountered and is broadly represented according to agent, model, and end point. These findings have broad-based implications for study design, risk assessment methods, and the establishment of optimal drug doses and suggest important evolutionarily adaptive strategies for dose-response relationships.

U-shaped dose-responses in biology, toxicology, and public health

The occurrence of U-shaped dose-response relationships (often termed hormesis) has been documented in numerous biological, toxicological, and pharmacological investigations. Many of the endpoints studied are of considerable significance to public health (e.g. body weight, cholesterol levels, ethanol consumption, longevity, cancer incidence, etc). Despite the fact that U-shaped dose-responses are widely and independently observed, little attempt has been made to assess this phenomenon in an integrative manner. This review provides an overview of the historical foundations of hormesis and a discussion of its definition within a mechanistic framework. The occurrence, generalizability, and biological significance of U-shaped dose-response relationships along with the concept of biological optimality are addressed.

Hormesis: a generalizable and unifying hypothesis

The present article represents a comprehensive effort to assess the hypothesis that hormesis is a highly generalizable biological phenomenon independent of environmental stressor, biological endpoint, and experimental model system. The evaluative methodology and complementary approaches employed to assess this question are (1) evolutionary biology-based theoretical paradigm; (2) evaluation of > 20,000 toxicology articles using a priori entry and evaluative criteria; (3) evaluation of 17 large-scale studies each providing data on numerous agents tested in the same experimental model by the same research team; (4) the assimilation of experimental pharmacological data on 24 receptor systems in which biphasic dose responses have been established reproducibly along with hormetic mechanism elucidation; and (5) assessment of the original hormesis database with 1600 dose-response relationships demonstrating evidence consistent with the hormesis hypothesis. The complementary approaches for assessing hormesis provided strong support for its credibility as a central biological theory based on its high frequency of occurrence and quantitative features of expression within microbe, plant, and invertebrate and vertebrate animal systems. The findings suggest that hormetic effects represent evolutionary-based adaptive responses to environmentally induced disruptions in homeostasis. Such adaptive responses, which are incorporated into organismal integrative physiological systems and now clarified at the mechanistic level for more than two dozen receptor systems, provide a cogent basis for the application of hormetic mechanisms in the elucidation of fundamental evolutionary-based biological processes and in the development of novel clinical modalities.

Agonist concentration gradients as a generalizable regulatory implementation strategy

This article proposes a general mechanism by which biphasic dose-response relationships occur in pharmacological and toxicological experimental systems. Such biphasic responses are mediated via a strategy of differential binding to stimulatory and inhibitory receptor subtypes based on agonist concentrations. Such a strategy is widely seen in pharmacological systems and has been demonstrated in toxicological-related biphasic dose responses in which the treatment altered levels of endogenous agonists.

Hormesis: U-shaped dose responses and their centrality in toxicology

The fundamental nature of the dose response is neither linear or threshold, but rather U-shaped. When studies are properly designed to evaluate biological activity below the traditional toxicological threshold, low-dose stimulatory responses are observed with high frequency and display specific quantitative features. With a few exceptions, the low-dose stimulatory response is usually not more than twofold greater than the control response, with a stimulatory zone that is more variable, ranging from less than tenfold to more than several orders of magnitude of the dose. Considerable mechanistic evidence indicates that hormetic effects represent overcompensation in response to disruptions in homeostasis that are mediated by agonist concentration gradients with different affinities for stimulatory and inhibitory regulatory pathways.

Tales of two similar hypotheses: the rise and fall of chemical and radiation hormesis

This paper compares the historical developments of chemical and radiation hormesis from their respective inceptions in the late 1880's for chemical hormesis and early 1900's for radiation hormesis to the mid 1930's to 1940 during which both hypotheses rose to some prominence but then became marginalized within the scientific community. This analysis documents that there were marked differences in their respective temporal developments, and the direction and maturity of research. In general, the formulation of the chemical hormesis hypothesis displayed an earlier, more-extensive and more sophisticated development than the radiation hormesis hypothesis. It was able to attract prestigious researchers with international reputations from leading institutions, to be the subject of numerous dissertations, to have its findings published in leading journals, and to have its concepts incorporated into leading microbiological texts. While both areas became the object of criticism from leading scientists, the intensity of the challenge was greatest for chemical hormesis due to its more visible association with the medical practice of homeopathy. Despite the presence of legitimate and flawed criticism, the most significant limitations of both chemical and radiation hormesis and their respective ultimate undoing were due to their: (1) lack of development of a coherent dose-response theory using data of low dose stimulation from both the chemical and radiation domains; (2) difficulty in replication of low dose stimulatory responses without an adequate study design especially with respect to an appropriate number and properly spaced doses below the toxic threshold; (3) modest degree of stimulation even under optimal conditions which was difficult to distinguish from normal variation; and (4) lack of appreciation of the practical and/or commercial applications of the concepts of low dose stimulation.

Radiation hormesis: its historical foundations as a biological hypothesis

This paper represents the first systematic effort to describe the historical foundations of radiation hormesis. Spanning the years from 1898 to the early 1940's the paper constructs and assesses the early history of such research and evaluates how advances in related scientific fields affected the course of hormetic related research. The present effort was designed to not only address this gap in current knowledge, but to offer a toxicological basis for how the concept of hormetic dose-response relationships may affect the nature of the bioassay and its role in the risk assessment process.

Chemical hormesis: its historical foundations as a biological hypothesis

Despite the long history of hormesis-related experimental research no systematic effort to describe its early history has been undertaken. The present paper attempts to reconstruct and assess the early history of such research and to evaluate how advances in related scientific fields affected the course of hormesis-related research. The purpose of this paper is not only to satisfy this gap in current knowledge, but also to provide a foundation for the assessment of how the concept of hormetic dose-response relationships may have affected the nature of the bioassay especially with respect to hazard assessment practices within a modern risk assessment framework.

Radiation hormesis: the demise of a legitimate hypothesis

This paper examines the underlying factors that contributed to the marginalization of radiation hormesis in the early and middle decades of the 20th century. The most critical factor affecting the demise of radiation hormesis was a lack of agreement over how to define the concept of hormesis and quantitatively describe its dose-response features. If radiation hormesis had been defined as a modest overcompensation to a disruption in homeostasis as would have been consistent with the prevailing notion in the area of chemical hormesis, this would have provided the theoretical and practical means to blunt subsequent legitimate criticism of this hypothesis. A second critical factor undermining the radiation hormesis hypothesis was the generally total lack of recognition by radiation scientists of the concept of chemical hormesis which was markedly more advanced, substantiated and generalized than in the radiation domain. The third factor was that major scientific criticism of low dose stimulatory responses was galvanized at the time that the National Research Council (NRC) was organizing a national research agenda on radiation and the hormetic hypothesis was generally excluded from the future planned research opportunities. Furthermore, the criticisms of the leading scientists of the 1930s which undermined the concept of radiation hormesis were limited in scope and highly flawed and then perpetuated over the decades by other 'prestigious' experts who appeared to simply accept the earlier reports. This setting was then linked to a growing fear of radiation as a cause of birth defects, mutation and cancer, factors all reinforced by later concerns over the atomic bomb. Strongly supportive findings on hormetic effects in the 1940s by Soviet scientists were either generally not available to US scientists or disregarded as part of the Cold War mindset without adequate analysis. Finally, a massive, but poorly designed, US Department of Agriculture experiment in the late 1940s to assess the capacity for low dose plant stimulation by radionuclides failed to support the hormetic hypothesis thereby markedly lessening enthusiasm for research and funding in this area. Thus, the combination of a failed understanding of the hormetic hypothesis and its linkage with a strong chemical hormesis database, flawed analyses by prestigious scientists at the critical stage of scientific research development, reinforced by a Cold War mentality led to marginalization of an hypothesis (i.e., radiation hormesis) that had substantial scientific foundations and generalizability.

The marginalization of hormesis

Despite the substantial development and publication of highly reproducible toxicological data, the concept of hormetic dose-response relationships was never integrated into the mainstream of toxicological thought. Review of the historical foundations of the interpretation of the bioassay and assessment of competitive theories of dose-response relationships lead to the conclusion that multiple factors contributed to the marginalization of hormesis during the middle and subsequent decades of the 20th century. These factors include: (a) the close-association of hormesis with homeopathy lead to the hostility of modern medicine toward homeopathy thereby creating a guilt by association framework, and the carry-over influence of that hostility in the judgements of medically-based pharmacologists/ toxicologists toward hormesis; (b) the emphasis of high dose effects linked with a lack of appreciation of the significance of the implications of low dose stimulatory effects; (c) the lack of an evolutionary-based mechanism(s) to account for hormetic effects; and (d) the lack of appropriate scientific advocates to counter aggressive and intellectually powerful critics of the hormetic perspective.

Hormesis: a highly generalizable and reproducible phenomenon with important implications for risk assessment

From a comprehensive search of the literature, the hormesis phenomenon was found to occur over a wide range of chemicals, taxonomic groups, and endpoints. By use of computer searches and extensive cross-referencing, nearly 3000 potentially relevant articles were identified. Evidence of chemical and radiation hormesis was judged to have occurred in approximately 1000 of these by use of a priori criteria. These criteria included study design features (e.g., number of doses, dose range), dose-response relationship, statistical analysis, and reproducibility of results. Numerous biological endpoints were assessed, with growth responses the most prevalent, followed by metabolic effects, reproductive responses, longevity, and cancer. Hormetic responses were generally observed to be of limited magnitude with an average maximum stimulation of 30 to 60 percent over that of the controls. This maximum usually occurred 4- to 5-fold below the NOAEL for a particular endpoint. The present analysis suggests that hormesis is a reproducible and generalizable biological phenomenon and is a fundamental component of many, if not most, dose-response relationships. The relatively infrequent observation of hormesis in the literature is believed to be due primarily to experimental design considerations, especially with respect to the number and range of doses and endpoint selection. Because of regulatory considerations, most toxicologic studies have been carried out at high doses above the low-dose region where the hormesis phenomenon occurs.

Chemical hormesis: its historical foundations as a biological hypothesis

Despite the long history of hormesis-related experimental research, no systematic effort to describe its early history has been undertaken. The present paper attempts to reconstruct and assess the early history of such research and to evaluate how advances in related scientific fields affected the course of hormesis-related research. The purpose of this paper is not only to satisfy this gap in current knowledge but also to provide a foundation for the assessment of how the concept of hormetic dose-response relationships may have affected the nature of the bioassay, especially with respect to hazard assessment practices within a modern risk assessment framework.

The marginalization of hormesis

Despite the substantial development and publication of highly reproducible toxicological data, the concept of hormetic dose-response relationships was never integrated into the mainstream of toxicological thought. Review of the historical foundations of the interpretation of the bioassay and assessment of competitive theories of dose-response relationships lead to the conclusion that multiple factors contributed to the marginalization of hormesis during the middle and subsequent decades of the 20th Century. These factors include the following: (a) the close association of hormesis with homeopathy, which led to the hostility of modern medicine toward homeopathy, thereby creating a guilt-by-association framework, and the carryover influence of that hostility toward hormesis in the judgements of medically based pharmacologists/toxicologists; (b) the emphasis of high-dose effects linked with a lack of appreciation of the significance of the implications of low-dose stimulatory effects; (c) the lack of an evolution-based mechanism(s) to account for hormetic effects; and (d) lack of appropriate scientific advocates to counter aggressive and intellectually powerful critics of the hormetic perspective.

Can the concept of hormesis Be generalized to carcinogenesis?

The concept of hormesis (i.e., low-dose stimulation/high-dose inhibition) has been shown to be widely generalizable with respect to chemical class, animal model, gender, and biological end point. The public health implication of this lack of linearity in the low-dose area of the dose-response curve raises the question of whether low doses of carcinogens will reduce cancer risk. Articles relating to the process of carcinogenesis (i.e., initiation, promotion, tumor development, and progression) were obtained from a recently developed chemical hormesis database and evaluated for their evidence of hormesis. Numerous examples in well-designed studies indicate that U- or J-shaped dose-response relationships exist with respect to various biomarkers of carcinogenesis in different animal models of both sexes. Examples of such J-shaped dose-response relationships in each stage of the process of carcinogenesis were selected for detailed toxicological examination. These results have important implications for both the hazard assessment of carcinogens and cancer risk assessment procedures.

A general classification of U-shaped dose-response relationships in toxicology and their mechanistic foundations

The development of a comprehensive database of chemical hormetic responses (i.e., U- or inverted U-shaped dose-response relationships) using objective a priori study design, statistical and study replication criteria has recently been reported. An assessment of this database reveals the existence of a wide range of hormetic dose-response relationships including those demonstrating a direct stimulation or an overcompensation response to a disruption of homeostasis. These two broad types of hormetic responses are affected by temporal factors and display unique patterns of dose-range stimulation, magnitude of stimulatory response and relationship of the maximum stimulatory response to the NOAEL. A general classification of U-shaped dose-response relationships is proposed to provide a more organized framework to evaluate the highly distinctive and diverse hormetic responses within the context of establishing underlying biological mechanisms and exploring risk assessment implications.

Hormesis as a biological hypothesis

A comprehensive effort was undertaken to identify articles demonstrating chemical hormesis. Nearly 4000 potentially relevant articles were retrieved from preliminary computer database searches by using various key word descriptors and extensive cross-referencing. A priori evaluation criteria were established including study design features (e.g., number of doses, dose range), statistical analysis, and reproducibility of results. Evidence of chemical hormesis was judged to have occurred in approximately 350 of the 4000 studies evaluated. Chemical hormesis was observed in a wide range of taxonomic groups and involved agents representing highly diverse chemical classes, many of potential environmental relevance. Numerous biological end points were assessed; growth responses were the most prevalent, followed by metabolic effects, longevity, reproductive responses, and survival. Hormetic responses were generally observed to be of limited magnitude. The average low-dose maximum stimulation was approximately 50% greater than controls. The hormetic dose-response range was generally limited to about one order of magnitude, with the upper end of the hormetic curve approaching the estimated no observable effect level for the particular end point. Based on the evaluation criteria, high to moderate evidence of hormesis was observed in studies comprised of > 6 doses; with > 3 doses in the hormetic zone. The present analysis suggests that chemical hormesis is a reproducible and relatively common biological phenomenon. A quantitative scheme is presented for future application to the database.

A toxicologically based weight-of-evidence methodology for the relative ranking of chemicals of endocrine disruption potential

A toxicologically based predictive scheme is presented for quantitatively ranking chemical agents with respect to their capacity to ensure endocrine disruption in target species based on short-term bioassays. Criteria providing the predictive framework include: (1) endocrine disruption as a multistage process, (2) phylogenetic considerations, (3) model system, and (4) estrogenic potency. Relative rankings were calculated for 15 environmentally relevant agents reported to have endocrine-disrupting effects. The relative ranking process offers a procedure for assessing the potential of endocrine disruption and for identifying data gaps for specific chemical agents. Although the current scheme is limited to "estrogenic" agents, it is anticipated that future refinements (e.g., incorporation of antiestrogenic potency data) will improve the system.

Potency ranking of methemoglobin-forming agents

This study represents the first systematic attempt to rank methemoglobin-forming agents. It is a quantitative potency ranking study utilizing linear regression analysis of dose-response data for comparative purposes. Six agents that are direct-acting and eight that require bioactivation were tested for their ability to induce methemoglobin formation in Dorset sheep erythrocytes under defined in vitro conditions. The agents were then ranked according to three complementary methods based on the slope of the linear regression, the calculated dose expected to induce a given amount of methemoglobin formation and the calculated percentage methemoglobin response induced by 1 mmol l-1 of the agent. The direct-acting agents, ranked from most to least potent inducers of methemoglobin formation, are: p-dinitrobenzene > o-dinitrobenzene > copper = nitrite > chlorite > chlorate. The ranking from most to least potent inducers of the bioactivated agents are: alpha-naphthol > p-nitroaniline > m-nitroaniline, o-nitroaniline > p-nitrotoluene = aniline > m-nitrotoluene = o-nitrotoluene. The ranking procedures are discussed and issues of interindividual variation and agent-specific sensitivities are addressed.

Decrease in hepatotoxicity by lead exposure is not explained by its mitogenic response

The present research was conducted to evaluate the effect of mitogen pre-exposure on CCl4-induced hepatotoxicity. Male Wistar rats were administered a single i.p. injection of CCl4 (0.3 ml kg-1 in corn oil) 48 h following either a single dose of lead nitrate (0.33 mg kg-1) or distilled water via i.v. injection. Hepatotoxicity, as measured by serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels, was monitored 6, 24, 48, 72 and 120 h after CCl4 exposure. The lead nitrate-pretreated rats displayed markedly lower serum ALT and AST levels at 24, 48 and 72 h than rats pretreated with distilled water. However, treatment with the antimitotic agent colchicine did not alter the lead-induced protection. These findings suggest that the lead-induced protection is not associated with the major mitogenic response of lead, despite its strong temporal association. A critical review of the available toxicological data also argues against the lead protection being a function of its capacity to inhibit cytochrome P-450.

Evaluation of a rodent peroxisome proliferator in two species of freshwater fish: rainbow trout (Onchorynchus mykiss) and Japanese medaka (Oryzias latipes)

Rainbow trout (Onchorynchus mykiss) and Japanese medaka (Oryzias latipes) were exposed to the hypolipidemic drug gemfibrozil, a known rodent peroxisome proliferator. Trout were injected (i.p.) daily for 2 weeks at doses of 0, 46, 87, or 152 mg/kg/day. Medaka were exposed to the nominal concentrations of 0, 1.25, 2.5, or 5 ppm in water for 2 weeks in a static-renewal system. Peroxisome proliferation was assessed by measuring fatty acyl-CoA oxidase (FAO) activity, peroxisomal bifunctional enzyme (PBE) quantity, and changes in liver-to-body weight ratios (LWR). Results indicate that a mild peroxisome proliferative response was observed in rainbow trout (significant increases in FAO activity at all dose levels and in LWR at the highest dose level). Medaka demonstrated a significant increase in PBE at the highest dose level, while nonsignificant increases in FAO activity were observed at the mid- and high-dose levels.

Gap junction-mediated intercellular communication in primary cultures of rainbow trout hepatocytes

Gap junction-mediated intercellular communication was evaluated in primary cultures of rainbow trout hepatocytes by measurement of dye coupling. Donor hepatocytes were microinjected with fluorescent Lucifer yellow CH dye and visualization of dye spread (dye coupling) to adjacent hepatocytes was recorded. A maximum level was reached between 8 and 12 hr which was maintained up to 24 hr. Dye coupling then decreased over the next 48 hr. Cell viability was monitored by the percentage of total LDH released and trypan blue exclusion at each time point. The effect of 12-O-tetradecanoylphorbol-13-acetate (TPA), a known inhibitor of rodent hepatic intercellular communication, on gap junction-mediated intercellular communication was evaluated in 24-hr cultures. A dose-response inhibition was demonstrated with maximum inhibition observed at 3 hr of exposure.

Tissue repair: a critical determinant in CCl4 hepatotoxicity

A single antimitotic dose of colchicine administered 24 hr after a single ip dose of CCl4 profoundly enhanced lethality in the adult Sprague-Dawley male rat from < 10% to over > or = 70% within the next 24 hr. These findings suggest that disruption of normal hepatic cellular repair processes is a critical factor affecting the outcome of CCl4 intoxication.

Improved method for selection of the NOAEL

The paper proposes that the NOAEL be defined as the highest dosage tested that is statistically significantly different from the control group while also being statistically significantly different from the LOAEL. This new definition requires that the NOAEL be defined from two points of reference rather than the current approach (i.e., single point of reference) in which the NOAEL represents only the highest dosage not statistically significantly different from the control group. This proposal is necessary in order to differentiate NOAELs which are statistically distinguishable from the LOAEL. Under the new regime only those satisfying both criteria would be designated a true NOAEL while those satisfying only one criteria (i.e., not statistically significant different from the control group) would be designated a "quasi" NOAEL and handled differently (i.e., via an uncertainty factor) for risk assessment purposes.

A toxicological basis to derive a generic interspecies uncertainty factor

A new method is proposed to derive the size of the interspecies uncertainty factor (UF) that is toxicologically and statistically based. The method involves quantifying interspecies variation in susceptibility to numerous toxic substances via the use of binary interspecies comparisons that are converted to a 95% UF. This interspecies UF represents an estimate of the upper 95% of the population of 95% prediction intervals (PI) for binary interspecies comparisons within four categories of phylogenetic relatedness (species within genus, genera within family, families within order, orders within class). The 95% interspecies UFs range from a low of 10 for species within genus up to 65 for orders within class. Most mammalian toxicology studies involving mice, rats, cats, dogs, gerbils, and rabbits are orders-within-class categories for human risk assessment and would be provided a 65-fold UF. Larger or smaller interspecies UF values could be selected on the level of protection desired.

Comparative response of rainbow trout and rat to the liver mitogen, lead

Lead nitrate and acetate are potent liver mitogens in the Wistar rat. Prior exposure to these agents has been found to alter their susceptibility to hepatotoxins. The present study assessed the capacity of both lead compounds to cause mitogenicity in the liver of adult male and female rainbow trout. Groups treated with a single intravenous or intraperitoneal injection of lead nitrate or lead acetate exhibited no statistically significant (P < 0.05) alterations in liver/body weight ratio nor hepatic DNA content. Results provide evidence of significant interspecies variation in the mitogenic response of rainbow trout and Wistar rats to the mitogenic potential of lead in the liver.

Effect of hypolipidemic drugs gemfibrozil, ciprofibrate, and clofibric acid on peroxisomal beta-oxidation in primary cultures of rainbow trout hepatocytes

Primary cultures of hepatocytes were established from sexually mature male rainbow trout (Oncorhyncus mykiss) and treated with the hypolipidemic drugs gemfibrozil (0.25-1.25 mM), clofibric acid (2.25-3.00 mM), or ciprofibrate (0.25-1.00 mM). Significant dose-related increases in peroxisomal fatty acyl-CoA oxidase (FACO) were seen after exposure for 48 hr to clofibric acid (P < 0.01) and ciprofibrate (P < 0.05) but not gemfibrozil (P = 0.08). Strong correlation was obtained between increased acyl-CoA oxidase activity and the relative amount of peroxisomal bifunctional enzyme (PBE), further supporting evidence of a proliferative effect. These preliminary studies demonstrate that peroxisomal beta-oxidation can be induced in vitro in a primary rainbow trout hepatocyte system.

G2 subpopulation in rat liver induced into mitosis by low-level exposure to carbon tetrachloride: an adaptive response

Recent findings by Mehendale (Med. Hypoth. 33, 289-299, 1990) indicate that prior exposure to chlordecone markedly enhances CCl4-induced lethality. It was established that chlordecone suppressed the capacity of CCl4-induced toxicity to cause an early (i.e., 6 hr after exposure) hepatocellular division which is believed to be a critical tissue response reducing subsequent CCl4-induced hepatotoxicity. Despite the strong evidence presented by Mehendale, occurrence of such an early cellular division has been considered unlikely since most studies indicate that cellular replacement requires from 30-60 hr depending on the agent, dose, and animal species. This paper presents evidence that supports the observations of Mehendale and indicates that the early mitoses were most likely caused by the activation of hepatocytes arrested in the G2 phase of the cell cycle that became activated by CCl4 treatment, induced injury, or both. The concept being put forward here requires additional experimental verification and validation.

Interactive potential of omega-3 fatty acids with clofibrate or DEHP on hepatic peroxisome proliferation in male Wistar rats

The interactive potential of three known peroxisome proliferators, omega-3 fatty acids, clofibrate and di(2-ethylhexylphthalate (DEHP), was evaluated in male weanling Wistar rats for the effect on peroxisomal beta-oxidation. Omega-3 fatty acids were supplied by menhaden oil which was fed in six regimens: low fat (5% w/w), low fat and clofibrate (0.3% w/w) or DEHP (0.25% w/w), high fat (20% w/w), high fat and clofibrate or DEHP in the aforementioned concentrations. Induction of peroxisomal beta-oxidation was measured by changes in liver-to-body weight ratio, fatty acyl-CoA oxidase (FAO) activity, and peroxisomal bifunctional enzyme (PBE) quantity. Analysis of transformed data indicated a less than additive response in FAO activity with no deviation from additivity seen with liver-to-body ratios and PBE.

Possible examples of chemical hormesis in a previously published study

A re-examination of data presented by Daston et al. provided an opportunity to assess the occurrence of chemical hormesis due to the wide dosage range tested and to the large number of treatments within the dosage range. The data revealed numerous examples of possible chemical hormesis for a variety of end-points measured.

The effect of peroxisome proliferators on S-phase synthesis in primary cultures of fish hepatocytes

The ability of seven structurally diverse peroxisome proliferators to induce S-phase synthesis was studied in primary cultures of rainbow trout and medaka hepatocytes. Cells were maintained in serum-free conditions designed to facilitate attachment, viability, and function. Lead nitrate, a well-known and potent rodent liver mitogen, was used in vitro in trout and medaka and in vivo in trout to evaluate the capacity of the species and our system to respond to mitogenic stimuli. S-phase synthesis induced by peroxosome proliferators did not result in any statistically significant increase over control cultures. These in vitro results are supported by in vivo data previously obtained and the present work with lead nitrate.

Ornithine decarboxylase (ODC) activity in the liver of individual medaka (Oryzias latipes) of both sexes

Ornithine decarboxylase (ODC) activity has been determined in the liver of individual medaka (N = 48). The results indicate a mean ODC activity of 1.69 +/- 1.77 nmol 14CO2/hr/mg protein. The fish displayed a large interindividual variation of normal ODC activity with a range of 140fold. However, no sex differences were observed. The findings also indicate that the mean ODC activity in this fish model is approximately 100fold greater than observations in the published literature as well as in our laboratory for commonly employed rodent models.