Reflections on chemical risk assessment or how (not) to serve society with science

In this paper, we want to shed light on the demand for chemical and toxicological data growing ever more faster than science can supply and other aspects of assessing chemical risks, including the demand for 'ever greater safety'. The treatise that follows is on the one hand rooted in well-established toxicological theory and on the other hand utilises emerging toxicological insights. Both theoretical conceptions and empirical substantiations are discussed to build up a perspective that produces an outlook on innovation and proliferates insights into our inexorable and invaluable exposure to 'the chemical'. We propose that in toxicology, with the implicit mandatory linear routine of dose-response, there is no tangible scientific drive to understand and unearth the actual empirical dose-response curve for chemicals under scrutiny. This can and should be improved upon as to advance the science of toxicology and to optimise current and future regulatory efforts.

Low-dose radiation therapy (LDRT) for COVID-19 and its deadlier variants

Coronavirus variants are gaining strongholds throughout the globe. Despite early signals that SARS-CoV-2 coronavirus case numbers are easing up in the United States and during the middle of a (not so easy) vaccination roll out, the country has passed a grim landmark of 600,000 deaths. We contend that these numbers would have been much lower if the medical community undertook serious investigations into the potential of low doses of radiation (LDRT) as a mainstream treatment modality for COVID-19 pneumonia. LDRT has been posited to manifest anti-infectious and anti-inflammatory properties at doses of 0.3-1.0 Gy via the activation of the Nrf-2 pathway. Although some researchers are conducting well-designed clinical trials on the potential of LDRT, the deep-rooted, blind, and flawed acceptance of the Linear No-Threshold (LNT) model for ionizing radiation has led to sidelining of this promising therapy and thus unimaginable numbers of deaths in the United States.

What Would Become of Nuclear Risk if Governments Changed Their Regulations to Recognize the Evidence of Radiation's Beneficial Health Effects for Exposures That Are Below the Thresholds for Detrimental Effects?

The 1953 Atoms for Peace Speech to the United Nations proposed applying nuclear energy to essential needs, including abundant electrical energy. The widespread fear of ionizing radiation from nuclear facilities and medical procedures began after the United States National Academy of Sciences performed a study of radiation dangers to the human genome. This study, initiated and managed by an oil industry benefactor, recommended in 1956 that the risk of radiation-induced mutations be assessed using the linear no-threshold dose-response model instead of the threshold model. It was followed by a study that wrongly linked low radiation to cancer among the atomic bomb survivors. The ensuing controversy resulted in a compromise. The National Committee on Radiation Protection adopted the precautionary principle policy in 1959, justified by fear of cancer and lack of knowledge. The United States and all other countries followed this recommendation, which remains unchanged 62 years later. Its impact on nuclear energy and medicine has been profound. Many costly regulations have been enacted to prevent very unlikely human or equipment failures-failures that would lead to radiation exposures that are below the dose thresholds for lasting harmful effects. Potential low-dose radiation therapies, against inflammation, cancer, autoimmune, and neurodegenerative diseases, are shunned.

Human periodontal ligament stem cells and hormesis: Enhancing cell renewal and cell differentiation

This paper provides a detailed assessment of hormetic dose responses by human periodontal ligament stem cells (hPDLSCs). Hormetic dose responses were induced by a broad range of chemicals, including dietary supplements (e.g., curcumin, ginsenoside Rg1), pharmaceutical/commercial substances (e.g., metformin) and endogenous agents (e.g., periostin, TNF-α) for cell proliferation/viability and osteogenic/adipocyte differentiation. This paper clarifies underlying mechanistic foundations of the hPLDSC hormetic dose responses and explores their therapeutic implications. Emerging evidence based on assessments of multiple types of stem cells shows hormetic dose responses to be widespread, reflecting considerable generality and a highly conserved evolutionary trait.

Micro/nanoplastics effects on organisms: A review focusing on 'dose'

Microplastics have become predominant contaminants, attracting much political and scientific attention. Despite the massively-increasing research on microplastics effects on organisms, the debate of whether environmental concentrations pose hazard and risk continues. This study critically reviews published literatures of microplastics effects on organisms within the context of "dose". It provides substantial evidence of the common occurrence of threshold and hormesis dose responses of numerous aquatic and terrestrial organisms to microplastics. This finding along with accumulated evidence indicating the capacity of organisms for recovery suggests that the linear-no-threshold model is biologically irrelevant and should not serve as a default model for assessing the microplastics risks. The published literature does not provide sufficient evidence supporting the general conclusion that environmental doses of microplastics cause adverse effects on individual organisms. Instead, doses that are smaller than the dose of toxicological threshold and more likely to occur in the environment may even induce positive effects, although the ecological implications of these responses remain unknown. This study also shows that low doses of microplastics can reduce whereas high doses can increase the negative effects of other pollutants. The mechanisms explaining these findings are discussed, providing a novel perspective for evaluating the risks of microplastics in the environment.

Ecological risks in a 'plastic' world: A threat to biological diversity?

Microplastics pollution is predicted to increase in the coming decades, raising concerns about its effects on living organisms. Although the effects of microplastics on individual organisms have been extensively studied, the effects on communities, biological diversity, and ecosystems remain underexplored. This paper reviews the published literature concerning how microplastics affect communities, biological diversity, and ecosystem processes. Microplastics increase the abundance of some taxa but decrease the abundance of some other taxa, indicating trade-offs among taxa and altered microbial community composition in both the natural environment and animals' gut. The alteration of community composition by microplastics is highly conserved across taxonomic ranks, while the alpha diversity of microbiota is often reduced or increased, depending on the microplastics dose and environmental conditions, suggesting potential threats to biodiversity. Biogeochemical cycles, greenhouse gas fluxes, and atmospheric chemistry, can also be altered by microplastics pollution. These findings suggest that microplastics may impact the U.N. Sustainability Development Goals (SDGs) to improve atmospheric, soil, and water quality and sustaining biodiversity.

Exogenous application of melatonin to plants, algae, and harvested products to sustain agricultural productivity and enhance nutritional and nutraceutical value: A meta-analysis

Melatonin is produced by plants, algae, and animals. Worldwide studies show diverse positive effects of exogenous melatonin on plants, edible plant products, and algae, but the potential of melatonin to enhance food and feed systems through these positive effects remains largely unexplored. Through a meta-analysis of about 25,000 observations, we show for the first time that exogenous application of melatonin significantly increases crop productivity and yields, and enhances the nutritional and nutraceutical value of edible plant products and algae by regulating diverse biological functions. We demonstrate that melatonin can improve plants, edible plant products, and algae under various current climate change scenarios, environmental pollution factors, and other stresses by about 7% to nearly 30%, on average, depending on the stressor. We also analyze various technical/methodological factors influencing the desired outcomes and identify conditions that offer optimal enhancement. We show that the positive effect of melatonin on plants and edible plant products varies among species, genera, and families, and strongly depends on the concentration of melatonin and treatment duration. The effect of melatonin is slightly lower on the monocot clade Commelinids than on the eudicot clades Asterids and Rosids. We also show that its stimulatory effect on plants depends on cultivation system, with a larger effect obtained in hydroponic systems. However, it does not depend on application stage (seed or vegetative), application route (foliage, roots, or seed), and whether the cultivation system is ex vivo or in vivo. This is the first meta-analysis examining the effects of melatonin on plants, edible plant products, and algae, and offers a scientific and technical roadmap facilitating sustainable food and feed production through the application of exogenous melatonin.

US EPA: Is there room to open a new window for evaluating potential sub-threshold effects and ecological risks?

With a rule published on 6 January 2021, the US Environmental Protection Agency (EPA) considers for the first time sub-threshold responses, abandoning the use of default dose-response models. This may affect worldwide scientific research, in terms of research design and methodology, and regulatory actions in China and other countries.

Luteolin and hormesis

The present paper provides the first integrated assessment of the capacity of luteolin to induce hormetic dose responses. It was shown that luteolin induced hormetic responses in multiple biological systems, including enhancing neuroprotection in various experimental model disease systems, improving wounding healing, especially in experimental models of high-risk population subgroups, such as diabetics, as well as enhancing osteogenesis in models of osteoporosis. The mechanistic basis for the luteolin-induced hormetic dose responses has been demonstrated to commonly involve the upregulation of the nuclear factor erythroid-derived 2-like 2 (Nrf2), which mediates the extensive range of anti-inflammatory effects induced by luteolin in multiple cell types and organ systems.

Hormesis and adult adipose-derived stem cells

This paper provides a detailed assessment of the occurrence of hormetic dose responses in adipose-derived stem cells (ADSCs) of animal models and humans. While a broad range of endpoints has been considered, the predominant research focus in the literature has involved cell proliferation and differentiation. Hormetic dose responses have been commonly reported for ADSCs, encompassing a broad range of chemicals, including pharmaceuticals, dietary supplements and endogenous agents as well as a broad range of physical stressors such as low frequency vibrations, electromagnetic frequency (EMF), heat and sound waves. Numerous agents upregulate key functions such as cell proliferation and differentiation in ADSCs, following the quantitative features of the hormesis dose response model. The paper also assesses the capacity of agents to selectively and dose-dependently activate cell proliferation and/or differentiation, their underlying mechanistic foundations and potential clinical implications. These findings indicate that hormetic dose responses are a prominent feature of ADSC biology and may have a determinant role in their potential clinical applications.

Redox modulation of vitagenes via plant polyphenols and vitamin D: Novel insights for chemoprevention and therapeutic interventions based on organoid technology

Polyphenols are chemopreventive through the induction of nuclear factor erythroid 2 related factor 2 (Nrf2)-mediated proteins and anti-inflammatory pathways. These pathways, encoding cytoprotective vitagenes, include heat shock proteins, such as heat shock protein 70 (Hsp70) and heme oxygenase-1 (HO-1), as well as glutathione redox system to protect against cancer initiation and progression. Phytochemicals exhibit biphasic dose responses on cancer cells, activating at low dose, signaling pathways resulting in upregulation of vitagenes, as in the case of the Nrf2 pathway upregulated by hydroxytyrosol (HT) or curcumin and NAD/NADH-sirtuin-1 activated by resveratrol. Here, the importance of vitagenes in redox stress response and autophagy mechanisms, as well as the potential use of dietary antioxidants in the prevention and treatment of multiple types of cancer are discussed. We also discuss the possible relationship between SARS-CoV-2, inflammation and cancer, exploiting innovative therapeutic approaches with HT-rich aqueous olive pulp extract (Hidrox®), a natural polyphenolic formulation, as well as the rationale of Vitamin D supplementation. Finally, we describe innovative approaches with organoids technology to study human carcinogenesis in preclinical models from basic cancer research to clinical practice, suggesting patient-derived organoids as an innovative tool to test drug toxicity and drive personalized therapy.

Formaldehyde: Another hormesis-inducing chemical

Formaldehyde (FA) is a naturally-occurring compound, produced endogenously in diverse living organisms. It also occurs widely in the environment due to anthropogenic (e.g. used as a chemical intermediate) and natural sources (e.g. a component of the volatile organic compounds blends emitted by plants). While FA is considered a potential carcinogen, living organisms have the ability to cope with FA, and some minimum endogenous levels of FA may be required for health. Recently, genetic engineering approaches transferring biological information from one organism to another led to increased assimilation of and conferred genetic-based tolerance to FA in plants-microorganisms systems. Here, we propose that FA commonly induces hormesis, a hypothesis that we confirm by collating evidence from various published studies with animals, plants, and microorganisms. The stimulation by low doses below the no-observed-adverse-effect-level (NOAEL) was modest in magnitude, in agreement with the general hormesis literature. In plants, among the endpoints showing hormesis were growth, lipid peroxidation, and photosynthetic pigments. In various animal cells, hormesis was observed in cell proliferation and viability, responses that were related to mechanisms, such as activation of phosphorylated ERK (extra-cellular signaling-regulated kinase) expression, acceleration of the process of cell division, and enhancement of the Warburg effect (i.e. use of glycolysis by tumor cells to produce energy for rapid growth). Hormetic in vitro responses were reported in several cancerous/tumorous cell lines, suggesting that FA has the potential to influence tumor promotion within a specific concentration range and biological context. These observations suggest that FA commonly acts in an hormetic manner with implications for study designs across a broad range of biological models and in the assessment of environmental and human risks associated with FA exposures.

Low-dose radiation therapy for osteoarthritis and enthesopathies: a review of current data

BACKGROUND

Osteoarthritis (OA), the most common degenerative joint disease, is associated with severe functional limitation and impairment of quality of life. Numerous reports have documented the clinical efficacy of low-dose radiotherapy (LD-RT) in the management of various inflammatory disorders, including OA. In this paper, we assessed the clinical literature involving the use of LD-RT in the treatment of OA, its dose-response features, possible underlying mechanistic features, and optimal therapeutic dose range.

METHODS

We carried out a systematic review based on the guidelines of the Preferred Reporting Items for Systematic Review and Meta-Analysis (PRISMA) statements and evaluated articles meeting the inclusion criteria for this review.

RESULTS

A total of 361 articles were identified from databases, such as Scopus, PubMed, Embase, and Science Direct out of which 224 articles were duplicates and were discarded. Of the remaining 137 articles, 74 articles were un-related, 27 articles were review articles, eight were conference abstracts, three were letters, two were editorials, two were notes, and one was a book chapter. Finally, 20 articles met all the inclusion criteria and were included in this systematic review.

DISCUSSION

Several single-arm retrospective/prospective studies showed advantages for LD-RT in the management of OA in terms of pain relief, improvement of mobility and function, and showed minimal side effects. Mechanistic considerations involve positive subcellular effects mediated by the activation of a nuclear factor erythroid 2-related transcription factor (Nrf2) mediated antioxidant response. Further research on both the short- and long-term effects of LD-RT on OA and other inflammatory disorders is recommended.

Hormesis: Transforming disciplines that rely on the dose response

This article tells the story of hormesis from its conceptual and experimental origins, its dismissal by the scientific and medical communities in the first half of the 20th century, and its rediscovery over the past several decades to be a fundamental evolutionary adaptive strategy. The upregulation of hormetic adaptive mechanisms has the capacity to decelerate the onset and reduce the severity of a broad spectrum of common age-related health, behavioral, and performance decrements and debilitating diseases, thereby significantly enhancing the human health span. Incorporation of hormetic-based lifestyle options within the human population would have profoundly positive impacts on the public health, significantly reducing health care costs.

Ferulic acid and hormesis: Biomedical and environmental implications

The present paper provides the first systematic assessment of the capacity of ferulic acid to induce hormetic dose responses in biological systems. Ferulic acid induced hormetic effects in a broad range of animal models, affecting numerous biological endpoints, with particular focus on neuroprotective effects. Emerging evidence in multiple biomedical systems indicates that the hormetic effects of ferulic acid depend upon the activation of the transcription factor Nrf2. Ferulic acid was also shown to have an important role in ecological settings, being routinely released into the environment by numerous plant species, acting as an allelopathic agent affecting the growth of neighboring species via hormetic dose responses. These findings demonstrate the potential ecological and biomedical importance of ferulic acid effects and that these effects are commonly expressed via the hormetic dose response, suggesting complex multisystem evolutionary regulatory strategies.

LNT and cancer risk assessment: Its flawed foundations part 2: How unsound LNT science became accepted

This paper argues that Edward B. Lewis served as a type of independent academic radiation LNT-cancer risk assessment-stalking horse for the BEAR Genetics Panel, a task for which he had no expertise or experience (e.g. radiation, leukemia, epidemiology and statistical modelling). His efforts produced an insufficiently documented, strongly biased, and high-profile paper in Science (May 17, 1957), whose principal conclusions had not been proven, he asserted privately, in writing. This inconclusive perspective was well camouflaged in the published paper by means of sophisticated wordsmithing. At the time his academic department head George Beadle came to chair the BEAR Genetics Panel in the summer of 1956, the Beadle-inspired-Lewis LNT activity acquired an urgency when a study of 70,000 offspring from survivors of the A-bombs failed to show genetic damage after a decade of careful study, undercutting Panel recommendations. With Beadle's guidance, the Lewis effort redirected the Panel's focus from the atomic bomb genetic damage study, which had acrimoniously disrupted Panel relationships and priorities, to more immediate disciplinary/professional opportunities with concerns about fallout, leukemia risks and a new cancer causation role for mutation. The serious limitations of the Lewis paper affected neither its publication in Science nor its receiving an editorial endorsement, possibly due to influence by powerful Panel members, such as Bentley Glass, one of only six senior editors for Science. The Science publication restored, even though improperly, the scientific and moral initiatives of the Panel and led directly to multiple high level LNT recommendations for cancer risk assessment based on the Precautionary Principle, which Lewis asserted, and which remains in place today in essentially all countries. The present paper explores how such a scientific long-shot and quasi-stalking horse, who was unsupported by BEAR Panel members during the withering criticism prompted by his Science article, nevertheless endured in the pursuit of his LNT goal, becoming strikingly successful in achieving a global cancer risk assessment revolution which remains in place.

LNT and cancer risk assessment: Its flawed foundations part 1: Radiation and leukemia: Where LNT began

This paper evaluates the scientific basis for the adoption of the linear non-threshold (LNT) dose response model for radiation-induced leukemia. This LNT risk assessment application for leukemia is significant because it: (1) was generalized for all tumor types induced by ionizing radiation and chemical carcinogens at relatively high doses and; (2) it was based on the mechanistic assumption of low dose linearity for somatic cell mutations as determined from responses in mature spermatozoa of fruit flies. A serious problem with the latter assumption is that those spermatozoa lack DNA repair. The acceptance of the LNT dose response model for cancer risk assessment was based on the convergence of recommendations of the BEAR I Genetics Panel (1956a) for reproductive cell gene mutations and those of Lewis (1957a) for somatic cell mutation and its capacity to explain apparent and/or predicted linear dose responses of ionizing radiation-induced leukemia in multiple and diverse epidemiological investigations. Use of that model and related dose response beliefs achieved rapid, widespread and enduring acceptance in the scientific and regulatory communities. They provide the key historical foundation for the sustained LNT-based policy for cancer risk assessment to the present. While previous papers in this series have challenged key scientific assessments and ethical foundations of the BEAR I Genetics Panel, the present paper provides evidence that Lewis: 1) incorrectly interpreted the fundamental scientific studies used to support the LNT conclusion even though such studies show consistent hormetic-J-shaped dose response relationships for leukemia in Hiroshima and Nagasaki survivors; and, 2) demonstrated widespread bias in support of an LNT conclusion and related policies, which kept him from making an objective and fair assessment. The LNT recommendation appears to have been uncritically accepted and integrated into scientific and regulatory practice in large part because it inappropriately appealed to existing authority and it garnered the support of those who were willing to risk greatly exaggerating the public's fears of environmentally-induced disease, such as enhanced risk of leukemia, with the goal of stopping the atmospheric testing of atomic bombs. Adoption of the LNT recommendation demonstrated extensive penetration of ideological influence affecting governmental, scientific and regulatory evaluation at the highest levels in the United States. This paper demonstrates that the scientific foundations for cancer risk assessment were inappropriately and inaccurately assessed, unethically adopted and require significant historical, scientific and regulatory remediation.

Demonstrated hormetic mechanisms putatively subserve riluzole-induced effects in neuroprotection against amyotrophic lateral sclerosis (ALS): Implications for research and clinical practice

This paper provides evidence to support that riluzole, an FDA-approved treatment for amyotrophic lateral sclerosis (ALS), like many neuroprotective agents, displays and exerts hormetic biphasic dose responses. These findings have important implications for the experimental study and clinical treatment of ALS.

Nrf2 activation putatively mediates clinical benefits of low-dose radiotherapy in COVID-19 pneumonia and acute respiratory distress syndrome (ARDS): Novel mechanistic considerations

Novel mechanistic insights are discussed herein that link a single, nontoxic, low-dose radiotherapy (LDRT) treatment (0.5–1.0 Gy) to (1) beneficial subcellular effects mediated by the activation of nuclear factor erythroid 2-related transcription factor (Nrf2) and to (2) favorable clinical outcomes for COVID-19 pneumonia patients displaying symptoms of acute respiratory distress syndrome (ARDS). We posit that the favorable clinical outcomes following LDRT result from potent Nrf2-mediated antioxidant responses that rebalance the oxidatively skewed redox states of immunological cells, driving them toward anti-inflammatory phenotypes. Activation of Nrf2 by ionizing radiation is highly dose dependent and conforms to the features of a biphasic (hormetic) dose–response. At the cellular and subcellular levels, hormetic doses of <1.0 Gy induce polarization shifts in the predominant population of lung macrophages, from an M1 pro-inflammatory to an M2 anti-inflammatory phenotype. Together, the Nrf2-mediated antioxidant responses and the subsequent shifts to anti-inflammatory phenotypes have the capacity to suppress cytokine storms, resolve inflammation, promote tissue repair, and prevent COVID-19-related mortality. Given these mechanistic considerations—and the historical clinical success of LDRT early in the 20th century—we opine that LDRT should be regarded as safe and effective for use at almost any stage of COVID-19 infection. In theory, however, optimal life-saving potential is thought to occur when LDRT is applied prior to the cytokine storms and before the patients are placed on mechanical oxygen ventilators. The administration of LDRT either as an intervention of last resort or too early in the disease progression may be far less effective in saving the lives of ARDS patients.

Smoke-water commonly induces hormetic dose responses in plants

A detailed evaluation was made of the literature concerning the dose response features of smoke-water extracts and other types of biological pyrolysis products on seed germination and plant growth. The evaluation was undertaken to extend our research on the occurrence and importance of hormesis in plant biology, as no similar assessment on smoke water biology had been published and that a preliminary survey suggested widespread occurrence of hormesis. It was determined that hormetic-like biphasic dose responses were commonly reported within the smoke-water plant literature for seed germination and plant growth. These findings were independent of the type of plant evaluated, the type of plant material used for the smoke-water extract, and the process of pyrolysis and extraction. The magnitude of the maximal stimulation of the biphasic dose responses was consistent with the hormetic concept, with maximal responses typically being approximately 30-60% greater than control values and with a stimulatory dose/concentration width less than 10 fold. These findings, which represent dose response features of a spectrum of novel and chemically diverse complex mixtures, support the generality of the hormetic dose response and its potential utility in enhancing the quality of study designs, including selection of dose/concentration number and spacing as well as biological model and endpoint.

Accumulator plants and hormesis

Accumulation of metals by plants is an important area of investigation in plant ecology and evolution as well as in soil contamination/phytoremediation practices. This paper reports that hormetic-biphasic dose-response relationships were commonly observed for multiple agents (i.e. arsenic, cadmium, chromium, fluoride, lead, and zinc) and 20 species in plant (hyper)accumulator studies. The hormetic stimulation was related to metal accumulation in affected tissues, with the metal stimulation concentration zone unique for each metal, species, tissue, and endpoint studied. However, quantitative features of the hormetic dose response were similar across all (hyper)accumulation studies, with results independent of plant species, endpoints measured, and metal. The dose-dependent stimulatory and inhibitory/toxic plant responses were often associated with the up- and down-regulation of adaptive mechanisms, especially those involving anti-oxidative enzymatic processes. These findings provide a mechanistic framework to account for both the qualitative and quantitative features of the hormetic dose response in plant (hyper)accumulator studies.

Pollen biology and hormesis: Pollen germination and pollen tube elongation

This paper evaluated the occurrence of hormetic dose responses in pollen reported over the past eight decades. Hormetic doses responses were induced by a wide range of chemical and physical agents in 34 plant species for pollen germination and pollen tube growth/elongation. Agents inducing such hormetic dose/concentration responses in pollen included nutrients, growth-promoting agents, plant and animal hormones, toxic substances, including heavy metals such as cadmium, gaseous pollutants such as ozone, as well as ionizing and non-ionizing radiation. This paper provides further evidence for the broad generality of the hormesis dose response, supporting substantial prior findings that the hormetic response is independent of biological model, inducing agent, and endpoints measured. Given the widespread potential of inducing hormetic dose responses in pollen, these findings indicate the need to explore their emerging biological, ecological, agricultural, economic and public health implications.

Hormesis Mediates Acquired Resilience: Using Plant-Derived Chemicals to Enhance Health

This review provides an assessment of hormesis, a highly conserved evolutionary dose-response adaptive strategy that leads to the development of acquired resilience within well-defined temporal windows. The hormetic-based acquired resilience has a central role in affecting healthy aging, slowing the onset and progression of numerous neurodegenerative and other age-related diseases, and reducing risks and damage due to heart attacks, stroke, and other serious conditions of public health and medical importance. The review provides the historical foundations of hormesis, its dose-response features, its capacity for generalization across biological models and endpoints measured, and its mechanistic foundations. The review also provides a focus on the adaptive features of hormesis, i.e., its capacity to upregulate acquired resilience and how this can be mediated by numerous plant-derived extracts, such as curcumin, ginseng, Ginkgo biloba, resveratrol, and green tea, that induce a broad spectrum of chemopreventive effects via hormesis.

Chloroquine commonly induces hormetic dose responses

The use of chloroquine in the treatment of COVID-19 has received considerable attention. The recent intense focus on this application of chloroquine stimulated an investigation into the effects of chloroquine at low doses on highly biologically-diverse models and whether it may induce hormetic-biphasic dose response effects. The assessment revealed that hormetic effects have been commonly induced by chloroquine, affecting numerous cell types, including tumor cell lines (e.g. human breast and colon) and non-tumor cell lines, enhancing viral replication, sperm motility, various behavioral endpoints as well as decreasing risks of convulsions, and enhancing a spectrum of neuroprotective responses within a preconditioning experimental framework. These diverse and complex findings indicate that hormetic dose responses commonly occur with chloroquine treatment with a range of biological models and endpoints. These findings have implications concerning study design features including the number and spacing of doses, and suggest a range of possible clinical concerns and opportunities depending on the endpoint considered.