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Lee H, Hanson HA, Logan J, Maguire D, Kapadia A, Dewji S, Agasthya G. Evaluating county-level lung cancer incidence from environmental radiation exposure, PM 2.5, and other exposures with regression and machine learning models. ENVIRONMENTAL GEOCHEMISTRY AND HEALTH 2024; 46:82. [PMID: 38367080 PMCID: PMC10874317 DOI: 10.1007/s10653-023-01820-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/18/2023] [Accepted: 11/27/2023] [Indexed: 02/19/2024]
Abstract
Characterizing the interplay between exposures shaping the human exposome is vital for uncovering the etiology of complex diseases. For example, cancer risk is modified by a range of multifactorial external environmental exposures. Environmental, socioeconomic, and lifestyle factors all shape lung cancer risk. However, epidemiological studies of radon aimed at identifying populations at high risk for lung cancer often fail to consider multiple exposures simultaneously. For example, moderating factors, such as PM2.5, may affect the transport of radon progeny to lung tissue. This ecological analysis leveraged a population-level dataset from the National Cancer Institute's Surveillance, Epidemiology, and End-Results data (2013-17) to simultaneously investigate the effect of multiple sources of low-dose radiation (gross [Formula: see text] activity and indoor radon) and PM2.5 on lung cancer incidence rates in the USA. County-level factors (environmental, sociodemographic, lifestyle) were controlled for, and Poisson regression and random forest models were used to assess the association between radon exposure and lung and bronchus cancer incidence rates. Tree-based machine learning (ML) method perform better than traditional regression: Poisson regression: 6.29/7.13 (mean absolute percentage error, MAPE), 12.70/12.77 (root mean square error, RMSE); Poisson random forest regression: 1.22/1.16 (MAPE), 8.01/8.15 (RMSE). The effect of PM2.5 increased with the concentration of environmental radon, thereby confirming findings from previous studies that investigated the possible synergistic effect of radon and PM2.5 on health outcomes. In summary, the results demonstrated (1) a need to consider multiple environmental exposures when assessing radon exposure's association with lung cancer risk, thereby highlighting (1) the importance of an exposomics framework and (2) that employing ML models may capture the complex interplay between environmental exposures and health, as in the case of indoor radon exposure and lung cancer incidence.
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Affiliation(s)
- Heechan Lee
- Nuclear and Radiological Engineering and Medical Physics Programs, George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, 770 State Street, Atlanta, GA, 30332, USA
- Advanced Computing for Health Sciences Section, Oak Ridge National Laboratory, 1 Bethel Valley Road, Oak Ridge, TN, 37830, USA
| | - Heidi A Hanson
- Advanced Computing for Health Sciences Section, Oak Ridge National Laboratory, 1 Bethel Valley Road, Oak Ridge, TN, 37830, USA
| | - Jeremy Logan
- Data Engineering Group, Data and AI Section, Oak Ridge National Laboratory, 1 Bethel Valley Road, Oak Ridge, TN, 37830, USA
| | - Dakotah Maguire
- Advanced Computing for Health Sciences Section, Oak Ridge National Laboratory, 1 Bethel Valley Road, Oak Ridge, TN, 37830, USA
| | - Anuj Kapadia
- Advanced Computing for Health Sciences Section, Oak Ridge National Laboratory, 1 Bethel Valley Road, Oak Ridge, TN, 37830, USA
| | - Shaheen Dewji
- Nuclear and Radiological Engineering and Medical Physics Programs, George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, 770 State Street, Atlanta, GA, 30332, USA
| | - Greeshma Agasthya
- Advanced Computing for Health Sciences Section, Oak Ridge National Laboratory, 1 Bethel Valley Road, Oak Ridge, TN, 37830, USA
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Calabrese EJ, Selby PB. Comet assay and hormesis. ENVIRONMENTAL POLLUTION (BARKING, ESSEX : 1987) 2024; 341:122929. [PMID: 37979647 DOI: 10.1016/j.envpol.2023.122929] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/08/2023] [Revised: 11/06/2023] [Accepted: 11/11/2023] [Indexed: 11/20/2023]
Abstract
The paper provides the first assessment of the occurrence of hormetic dose responses using the Comet assay, a genotoxic assay. Using a priori evaluative criteria based on the Hormetic Database on peer-reviewed comet assay experimental findings, numerous examples of hormetic dose responses were obtained. These responses occurred in a large and diverse range of cell types and for agents from a broad range of chemical classes. Limited attempts were made to estimate the frequency of hormesis within comet assay experimental studies using a priori entry and evaluative criteria, with results suggesting a frequency in the 40% range. These findings are important as they show that a wide range of genotoxic chemicals display evidence that is strongly suggestive of hormetic dose responses. These findings have significant implications for study design issues, including the number of doses selected, dose range and spacing. Likewise, the widespread occurrence of hormetic dose responses in this genotoxic assay has important risk assessment implications.
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Affiliation(s)
- Edward J Calabrese
- Department of Environmental Health Sciences, Morrill I, N344, University of Massachusetts, Amherst, MA, 01003, USA.
| | - Paul B Selby
- Retired from Oak Ridge National Laboratory at Oak Ridge, TN. Home Address: 4088 Nottinghill Gate Road, Upper Arlington, OH, 43220, USA.
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Selby PB, Calabrese EJ. How self-interest and deception led to the adoption of the linear non-threshold dose response (LNT) model for cancer risk assessment. THE SCIENCE OF THE TOTAL ENVIRONMENT 2023; 898:165402. [PMID: 37454843 DOI: 10.1016/j.scitotenv.2023.165402] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/09/2023] [Revised: 07/06/2023] [Accepted: 07/06/2023] [Indexed: 07/18/2023]
Abstract
This paper clarifies scientific contributions and deceptive/self-serving decisions of William L. Russell and Liane Russell that led to the adoption of the linear non-threshold (LNT) model for cancer risk assessment by the US EPA. By deliberately failing to report an extremely large cluster of mutations in the control group of their first experiment, and thereby greatly suppressing its mutation rate, the Russells incorrectly claimed that the male mouse was 15-fold more susceptible to ionizing-radiation-induced gene mutations as compared with fruit flies. This self-serving error not only propelled their research program into one of great prominence, but it also promoted the LNT-based doubling dose (DD) concept in radiation genetics/cancer risk assessment, by the US National Academy of Sciences (NAS) Biological Effects of Atomic Radiation (BEAR) I Genetics Panel (1956). The DD concept became a central element in their recommendation that regulatory agencies switch from a threshold to an LNT model. This error occurred because of a decision by W. Russell not to report that a large cluster of control group mutations found in an experiment for which preliminary results were reported in 1951. This failure to report that cluster and similar clusters continued throughout the careers of the Russells, resulting in massive overestimation of low dose radiation risks supporting the LNT. The Russell database and the repeated claim that those data show that there is no threshold dose rate for mutation in irradiated mouse stem-cell spermatogonia, have provided mechanistic validation supporting the epidemiological LNT hypothesis for radiation-induced leukemias and cancers. This reanalysis supports the threshold model for both males and females, thereby rebutting epidemiological extrapolations from the NAS and EPA claiming support for the LNT hypothesis for cancer risk assessment. The implications of the Russell errors/deceptions, how/why they occurred, and their impact upon society are enormous and need to be addressed by scientific/regulatory agencies, affecting regulatory and litigation activities.
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Affiliation(s)
- Paul B Selby
- Retired from Oak Ridge National Laboratory at Oak Ridge, TN, Home Address: 4088 Nottinghill Gate Road, Upper Arlington, OH 43220, USA
| | - Edward J Calabrese
- Department of Environmental Health Sciences, Morrill I, N344, University of Massachusetts, Amherst, MA 01003, USA.
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Tang H, Cai L, He X, Niu Z, Huang H, Hu W, Bian H, Huang H. Radiation-induced bystander effect and its clinical implications. Front Oncol 2023; 13:1124412. [PMID: 37091174 PMCID: PMC10113613 DOI: 10.3389/fonc.2023.1124412] [Citation(s) in RCA: 9] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2022] [Accepted: 03/24/2023] [Indexed: 04/08/2023] Open
Abstract
For many years, targeted DNA damage caused by radiation has been considered the main cause of various biological effects. Based on this paradigm, any small amount of radiation is harmful to the organism. Epidemiological studies of Japanese atomic bomb survivors have proposed the linear-non-threshold model as the dominant standard in the field of radiation protection. However, there is increasing evidence that the linear-non-threshold model is not fully applicable to the biological effects caused by low dose radiation, and theories related to low dose radiation require further investigation. In addition to the cell damage caused by direct exposure, non-targeted effects, which are sometimes referred to as bystander effects, abscopal effects, genetic instability, etc., are another kind of significant effect related to low dose radiation. An understanding of this phenomenon is crucial for both basic biomedical research and clinical application. This article reviews recent studies on the bystander effect and summarizes the key findings in the field. Additionally, it offers a cross-sectional comparison of bystander effects caused by various radiation sources in different cell types, as well as an in-depth analysis of studies on the potential biological mechanisms of bystander effects. This review aims to present valuable information and provide new insights on the bystander effect to enlighten both radiobiologists and clinical radiologists searching for new ways to improve clinical treatments.
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Affiliation(s)
- Haoyi Tang
- State Key Laboratory of Radiation Medicine and Protection, School of Radiation Medicine and Protection, Collaborative Innovation Center of Radiological Medicine of Jiangsu Higher Education Institutions, Soochow University, Suzhou, China
| | - Luwei Cai
- State Key Laboratory of Radiation Medicine and Protection, School of Radiation Medicine and Protection, Collaborative Innovation Center of Radiological Medicine of Jiangsu Higher Education Institutions, Soochow University, Suzhou, China
| | - Xiangyang He
- State Key Laboratory of Radiation Medicine and Protection, School of Radiation Medicine and Protection, Collaborative Innovation Center of Radiological Medicine of Jiangsu Higher Education Institutions, Soochow University, Suzhou, China
| | - Zihe Niu
- State Key Laboratory of Radiation Medicine and Protection, School of Radiation Medicine and Protection, Collaborative Innovation Center of Radiological Medicine of Jiangsu Higher Education Institutions, Soochow University, Suzhou, China
| | - Haitong Huang
- State Key Laboratory of Radiation Medicine and Protection, School of Radiation Medicine and Protection, Collaborative Innovation Center of Radiological Medicine of Jiangsu Higher Education Institutions, Soochow University, Suzhou, China
| | - Wentao Hu
- State Key Laboratory of Radiation Medicine and Protection, School of Radiation Medicine and Protection, Collaborative Innovation Center of Radiological Medicine of Jiangsu Higher Education Institutions, Soochow University, Suzhou, China
- *Correspondence: Hao Huang, ; Huahui Bian, ; Wentao Hu,
| | - Huahui Bian
- Nuclear and Radiation Incident Medical Emergency Office, The Second Affiliated Hospital of Soochow University, Suzhou, China
- *Correspondence: Hao Huang, ; Huahui Bian, ; Wentao Hu,
| | - Hao Huang
- State Key Laboratory of Radiation Medicine and Protection, School of Radiation Medicine and Protection, Collaborative Innovation Center of Radiological Medicine of Jiangsu Higher Education Institutions, Soochow University, Suzhou, China
- *Correspondence: Hao Huang, ; Huahui Bian, ; Wentao Hu,
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Linear non-threshold (LNT) fails numerous toxicological stress tests: Implications for continued policy use. Chem Biol Interact 2022; 365:110064. [DOI: 10.1016/j.cbi.2022.110064] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2022] [Revised: 06/24/2022] [Accepted: 07/18/2022] [Indexed: 11/16/2022]
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Ricci PF, Calabrese EJ. Resolving an Open Science-policy question: Should the LNT still be an omnibus regulatory assumption? THE SCIENCE OF THE TOTAL ENVIRONMENT 2022; 825:153917. [PMID: 35189226 DOI: 10.1016/j.scitotenv.2022.153917] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/13/2022] [Revised: 02/11/2022] [Accepted: 02/12/2022] [Indexed: 06/14/2023]
Abstract
Regulatory analyses, modeling the carcinogenic effect of ionizing radiations (IR) (e.g., alpha and beta particles, x-, and gamma rays, neutrons) and chemicals continue to use the linear no-threshold (LNT) model from zero to some low dose. The LNT is an omnibus causal default in regulatory occupational and health risk analysis. Its use raises four issues that make this default an open question. The first is that the LNT applied to study a single agent excludes co-exposure to other known risk factors: physical, dietary, socio-economic, and other. Causation is inappropriately specified because cancer incidence is imputed to the single agent's doses, although most cancers are multifactorial diseases. The second, linear interpolation from high to zero dose and response, is incorrect because biological and epidemiological evidence identify different mechanisms and modes of action at those doses. Third, additivity of exposure effect to background effect is questionable and certainly variable. Fourth, the default overestimates the probabilities and consequences at low doses, supplanting rational decision-making in which alternative models may be more or less likely to be correct. Recent converging scientific evidence against the LNT hypothesis answers the open question. The LNT use in regulation conflates science with administrative ease and risk aversion by policymakers. It should be replaced by models that are based on biologically motivated mechanistic understandings within an evolutionary biology framework that integrates adaptive strategies/processes in their formulation.
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Affiliation(s)
- Paolo F Ricci
- University of Bologna, Environmental Management, Ravenna Campus, Scienze Ambientali, Via Sant'Alberto 163, 48123, Ravenna, Italy.
| | - Edward J Calabrese
- Environmental Health Sciences, Morrill I, N344, University of Massachusetts, Amherst, MA 01003, USA.
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Ghosh A. Biological and cellular responses of humans to high-level natural radiation: A clarion call for a fresh perspective on the linear no-threshold paradigm. MUTATION RESEARCH. GENETIC TOXICOLOGY AND ENVIRONMENTAL MUTAGENESIS 2022; 878:503478. [PMID: 35649671 DOI: 10.1016/j.mrgentox.2022.503478] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/23/2021] [Revised: 03/04/2022] [Accepted: 03/04/2022] [Indexed: 06/15/2023]
Abstract
There remains considerable uncertainty in obtaining risk estimates of adverse health outcomes of chronic low-dose radiation. In the absence of reliable direct data, extrapolation through the linear no-threshold (LNT) hypothesis forms the cardinal tenet of all risk assessments for low doses (≤ 100 mGy) and for the radiation protection principle of As Low As Reasonably Achievable (ALARA). However, as recent evidences demonstrate, LNT assumptions do not appropriately reflect the biology of the cell at the low-dose end of the dose-response curve. In this regard, human populations living in high-level natural radiation areas (HLNRA) of the world can provide valuable insights into the biological and cellular effects of chronic radiation to facilitate improved precision of the dose-response relationship at low doses. Here, data obtained over decades of epidemiological and radiobiological studies on HLNRA populations is summarized. These studies do not show any evidence of unfavourable health effects or adverse cellular effects that can be correlated with high-level natural radiation. Contrary to the assumptions of LNT, no excess cancer risks or untoward pregnancy outcomes have been found to be associated with cumulative radiation dose or in-utero exposures. Molecular biology-driven studies demonstrate that chronic low-dose activates several cellular defence mechanisms that help cells to sense, recover, survive, and adapt to radiation stress. These mechanisms include stress-response signaling, DNA repair, immune alterations and most importantly, the radiation-induced adaptive response. The HLNRA data is consistent with the new evolving paradigms of low-dose radiobiology and can help develop the theoretical framework of an alternate dose-response model. A rational integration of radiobiology with epidemiology data is imperative to reduce uncertainties in predicting the potential health risks of chronic low doses of radiation.
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Affiliation(s)
- Anu Ghosh
- Animal House Facility & Radiation Signaling Section, Radiation Biology & Health Sciences Division, Bio-Science Group, Bhabha Atomic Research Centre, Mumbai 400 085, India; Homi Bhabha National Institute (HBNI), Anushaktinagar, Mumbai 400 094, India.
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8
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De Roo B, Bacher K, Verstraete K. Cervical and lumbar spine imaging after traffic and occupational accidents: Evaluation of the use of imaging techniques, cumulative radiation dose and associated lifetime cancer risk. Eur J Radiol 2022; 151:110293. [DOI: 10.1016/j.ejrad.2022.110293] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2022] [Revised: 03/14/2022] [Accepted: 03/31/2022] [Indexed: 11/15/2022]
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9
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Auditore L, Pistone D, Amato E, Italiano A. Monte Carlo methods in nuclear medicine. Nucl Med Mol Imaging 2022. [DOI: 10.1016/b978-0-12-822960-6.00136-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022] Open
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10
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Lopes MA, Coleman RR, Cremata EJ. Radiography and Clinical Decision-Making in Chiropractic. Dose Response 2021; 19:15593258211044844. [PMID: 34675758 PMCID: PMC8524714 DOI: 10.1177/15593258211044844] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2021] [Revised: 08/11/2021] [Accepted: 08/17/2021] [Indexed: 12/25/2022] Open
Abstract
The concern over x-ray exposure risks can overshadow the potential benefit of radiography, especially in cases where manual therapy is employed. Spinal malalignment cannot be accurately visualized without imaging. Manual therapy and the load tolerances of injured spinal tissues raise different criteria for the use of x-rays for spinal disorders than in medical practice. Current regulatory bodies rely on radiography risk assessments based on Linear-No-Threshold (LNT) risk models. There is a need to consider radiography guidelines for chiropractic which are different from those for medical practice. Radiography practice guidelines are summaries dominated by frequentist interpretations in the analysis of data from studies. In contrast, clinicians often employ a pseudo-Bayesian form of reasoning during the clinical decision-making process. The overrepresentation of frequentist perspectives in evidence-based practice guidelines alter decision-making away from practical assessment of a patient's needs, toward an overly cautious standard applied to patients without regard to their risk/benefit likelihoods relating to radiography. Guidelines for radiography in chiropractic to fully assess the condition of the spine and spinal alignment prior to manual therapy, especially with high velocity, low amplitude spinal manipulation (HVLA-SM), should necessarily differ from those used in medical practice.
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Affiliation(s)
- Mark A. Lopes
- Gonstead Clinical Studies Society, Santa Cruz, CA, USA
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Oakley PA, Betz JW, Harrison DE, Siskin LA, Hirsh DW. Radiophobia Overreaction: College of Chiropractors of British Columbia Revoke Full X-Ray Rights Based on Flawed Study and Radiation Fear-Mongering. Dose Response 2021; 19:15593258211033142. [PMID: 34421439 PMCID: PMC8375354 DOI: 10.1177/15593258211033142] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2021] [Revised: 06/17/2021] [Accepted: 06/22/2021] [Indexed: 01/11/2023] Open
Abstract
Fears over radiation have created irrational pressures to dissuade radiography use within chiropractic. Recently, the regulatory body for chiropractors practicing in British Columbia, Canada, the College of Chiropractors of British Columbia (CCBC), contracted Pierre Côté to review the clinical use of X-rays within the chiropractic profession. A "rapid review" was performed and published quickly and included only 9 papers, the most recent dating from 2005; they concluded, "Given the inherent risks of radiation, we recommend that chiropractors do not use radiographs for the routine and repeat evaluation of the structure and function of the spine." The CCBC then launched an immediate review of the use of X-rays by chiropractors in their jurisdiction. Member and public opinion were gathered but not presented to their members. On February 4, 2021, the College announced amendments to their Professional Conduct Handbook that revoked X-ray rights for routine/repeat assessment and management of patients with spine disorders. Here, we highlight current and historical evidence that substantiates that X-rays are not a public health threat. We also point out critical and insurmountable flaws in the single paper used to support irrational and unscientific policy that discriminates against chiropractors who practice certain forms of evidence-based X-ray-guided methods.
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Affiliation(s)
| | | | | | | | | | - International Chiropractors Association Rapid Response Research Review Subcommittee
- Private Practice, Newmarket, ON, Canada
- Private Practice, Boise, ID, USA
- CBP NonProfit, Inc, Eagle, ID, USA
- Private Practice, Green Brook, NJ, USA
- Private Practice, Laurel, MD, USA
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Puukila S, Tharmalingam S, Al-Khayyat W, Peterson J, Hooker AM, Muise S, Boreham DR, Dixon DL. Transcriptomic Response in the Spleen after Whole-Body Low-Dose X-Ray Irradiation. Radiat Res 2021; 196:66-73. [PMID: 33956160 DOI: 10.1667/rade-20-00267.1] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2020] [Accepted: 04/02/2021] [Indexed: 11/03/2022]
Abstract
As the use of medical radiation procedures continues to rise, it is imperative to further our understanding of the effects of this exposure. The spleen is not known as a particularly radiosensitive organ, although its tolerance to radiation is not well understood. Low-dose radiation exposure has been implicated in beneficial responses, particularly in cell death and DNA damage repair. In this study, adult male rats received 2, 20, 200 mGy or 4 Gy whole-body X-ray irradiation and the transcriptional response in the spleen was analyzed at 0.5, 4 and 24 h postirradiation. We analyzed expression of genes involved in apoptosis, cell cycle progression and DNA damage repair. As expected, 4 Gy irradiated animals demonstrated elevated expression of genes related to apoptosis at 0.5, 4 and 24 h postirradiation in the spleen. These animals also showed upregulation of DNA damage repair genes at 24 h postirradiation. Interestingly, the spleens of 20 mGy irradiated animals showed reduced apoptosis and cell cycle arrest compared to the spleens of sham-irradiated animals. These results further reveal that the cellular response in the spleen to whole-body irradiation differs between low- and high-dose irradiation.
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Affiliation(s)
- S Puukila
- College of Medicine and Public Health, Flinders University, Adelaide, SA, Australia.,Laurentian University, Sudbury, Canada
| | - S Tharmalingam
- Laurentian University, Sudbury, Canada.,Northern Ontario School of Medicine, Sudbury/Thunder Bay, Canada.,Health Sciences North Research Institute, Sudbury, Canada
| | | | | | - A M Hooker
- College of Medicine and Public Health, Flinders University, Adelaide, SA, Australia.,Centre for Radiation Research Education and Innovation, University of Adelaide, Adelaide, Australia
| | - S Muise
- McMaster University, Hamilton, Canada
| | - D R Boreham
- Northern Ontario School of Medicine, Sudbury/Thunder Bay, Canada
| | - D-L Dixon
- College of Medicine and Public Health, Flinders University, Adelaide, SA, Australia.,Northern Ontario School of Medicine, Sudbury/Thunder Bay, Canada
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Thresholds for carcinogens. Chem Biol Interact 2021; 341:109464. [PMID: 33823170 DOI: 10.1016/j.cbi.2021.109464] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2021] [Revised: 03/28/2021] [Accepted: 03/29/2021] [Indexed: 02/07/2023]
Abstract
Current regulatory cancer risk assessment principles and practices assume a linear dose-response relationship-the linear no-threshold (LNT) model-that theoretically estimates cancer risks occurring following low doses of carcinogens by linearly extrapolating downward from experimentally determined risks at high doses. The two-year rodent bioassays serve as experimental vehicles to determine the high-dose cancer risks in animals and then to predict, by extrapolation, the number of carcinogen-induced tumors (tumor incidence) that will arise during the lifespans of humans who are exposed to environmental carcinogens at doses typically orders of magnitude below those applied in the rodent assays. An integrated toxicological analysis is conducted herein to reconsider an alternative and once-promising approach, tumor latency, for estimating carcinogen-induced cancer risks at low doses. Tumor latency measures time-to-tumor following exposure to a carcinogen, instead of tumor incidence. Evidence for and against the concept of carcinogen-induced tumor latency is presented, discussed, and then examined with respect to its relationship to dose, dose rates, and the dose-related concepts of initiation, tumor promotion, tumor regression, tumor incidence, and hormesis. Considerable experimental evidence indicates: (1) tumor latency (time-to-tumor) is inversely related to the dose of carcinogens and (2) lower doses of carcinogens display quantifiably discrete latency thresholds below which the promotion and, consequently, the progression and growth of tumors are delayed or prevented during a normal lifespan. Besides reconciling well with the concept of tumor promotion, such latency thresholds also reconcile favorably with the existence of thresholds for tumor incidence, the stochastic processes of tumor initiation, and the compensatory repair mechanisms of hormesis. Most importantly, this analysis and the arguments presented herein provide sound theoretical, experimental, and mechanistic rationales for rethinking the foundational premises of low-dose linearity and updating the current practices of cancer risk assessment to include the concept of carcinogen thresholds.
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14
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Calabrese EJ. The Muller-Neel dispute and the fate of cancer risk assessment. ENVIRONMENTAL RESEARCH 2020; 190:109961. [PMID: 32810676 DOI: 10.1016/j.envres.2020.109961] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/17/2020] [Revised: 07/14/2020] [Accepted: 07/15/2020] [Indexed: 06/11/2023]
Abstract
The National Academy of Sciences (NAS) Atomic Bomb Casualty Commission (ABCC) human genetic study (i.e., The Neel and Schull, 1956a report) showed an absence of genetic damage in offspring of atomic bomb survivors in support of a threshold model, but was not considered for evaluation by the NAS Biological Effects of Atomic Radiation (BEAR) I Genetics Panel. The study therefore could not impact the Panel's decision to recommend the linear non-threshold (LNT) dose-response model for risk assessment. Summaries and transcripts of the Panel meetings failed to reveal an evaluation of this study, despite its human relevance and ready availability, relying instead on data from Drosophila and mice. This paper explores correspondence among and between BEAR Genetics Panel members, including James Néel, the study director, and other contemporaries to assess why the Panel failed to use these data and how the decision to recommend the LNT model affected future cancer risk assessment policies and practices. This failure of the Genetics Panel was due to: (1) a strongly unified belief in the LNT model among panel members and their refusal to acknowledge that a low dose of radiation could exhibit a threshold, a conclusion that the Néel/Schull atomicbomb study could support, and (2) an excessive degree of self-interest among panel members who experimented with animal models, such as Hermann J. Muller, and feared that human genetic studies would expose the limitations of extrapolating from animal (especially Drosophila) to human responses and would strongly shift research investments/academic grants from animal to human studies. Thus, the failure to consider the Néel/Schull atomic bomb study served both the purposes of preserving the LNT policy goal and ensuring the continued dominance of Muller and his similarly research-oriented colleagues.
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Affiliation(s)
- Edward J Calabrese
- Professor of Toxicology, Environmental Health Sciences, Morrill I, N344, University of Massachusetts, Amherst, MA, 01003, USA.
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15
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Sykes PJ. Until There Is a Resolution of the Pro-LNT/Anti-LNT Debate, We Should Head Toward a More Sensible Graded Approach for Protection From Low-Dose Ionizing Radiation. Dose Response 2020; 18:1559325820921651. [PMID: 32425725 PMCID: PMC7218310 DOI: 10.1177/1559325820921651] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2020] [Revised: 04/01/2020] [Accepted: 04/03/2020] [Indexed: 01/19/2023] Open
Abstract
Current regulation of ionizing radiation is based on the linear no-threshold (LNT) model where any radiation dose increases cancer risk and is independent of dose rate, resulting in large amounts of time and money being spent protecting from extremely small radiation exposures and hence extremely small risk. There are animal studies which demonstrate that LNT is incorrect at low doses, supporting a threshold or hormesis model and thus indicating that there is no need to protect from very low doses. This has led to a sometimes bitter debate between pro-LNT and anti-LNT camps, and the debate has been at a stalemate for some time. This commentary is not aimed at taking either side of the debate. It is likely that the public, workers, and the environment are adequately protected under current regulation, which is the most important outcome. Until those on one side of the debate can convince the other, it would be sensible to move forward toward a graded (risk-based) approach to regulation, where the stringency of control is commensurate with the risk, resulting hopefully in more sensible practical thresholds. This approach is gradually being put forward by international radiation protection advisory bodies.
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Affiliation(s)
- Pamela J Sykes
- Flinders Centre for Innovation in Cancer, College of Medicine and Public Health, Flinders University. Adelaide, South Australia, Australia
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