Modulation of the Epileptic Seizure Threshold: Implications of Biphasic Dose Responses

The chemoprotective hormetic effects of rosmarinic acid

Rosmarinic acid is a polyphenol found in numerous fruits and vegetables, consumed in supplement form, and tested in numerous clinical trials for therapeutic applications due to its putative chemopreventive properties. Rosmarinic acid has been extensively studied at the cellular, whole animal, and molecular mechanism levels, presenting a complex array of multi-system biological effects. Rosmarinic acid-induced hormetic dose responses are widespread, occurring in numerous biological models and cell types for a broad range of endpoints. Consequently, this article provides the first assessment of rosmarinic acid-induced hormetic concentration/dose responses, their quantitative features, mechanistic foundations, extrapolative strengths/limitations, and their biomedical, clinical, and public health implications.

Stimulatory and inhibitory effects of morphine on pentylenetetrazol-induced epileptic activity in rat

AIMS

The present study attempts to evaluate the effects of different doses of morphine on experimental epileptiform activity caused by pentylenetetrazol (PTZ) in rats.

METHODS

Thirty adult male rats were assigned to saline (n = 5), morphine (2, 5, and 10 mg/kg, n = 15), naloxone (1 mg/kg, n = 5), and pre-treated with naloxone+morphine (1 + 10 mg/kg, n = 5) groups. The animals were anesthetized with ketamine + xylazine (80 + 8 mg/kg), and then a bipolar electrode was implanted into the CA1 (AP: -2.76 mm, ML: -1.4 mm and DV: 3 mm). To evaluate the effects of drugs on spike count and their amplitudes by elab amplifier, after drug administration for 25 min, PTZ (80 mg/kg, i.p.) was injected to induce epileptiform activity. Finally, diazepam (10 mg/kg) was used to suppress epileptic activity.

RESULTS

The results revealed that morphine at a dose of 2 mg/kg decreased, and at doses of 5 and 10 mg/kg had an increasing effect on seizure-like events (SLEs). Nevertheless, morphine at a dose of 10 mg/kg enhanced SLEs significantly (p < 0.01). Naloxone at a dose of 1 mg/kg had no significant effect on the spike count but increased amplitude of them (p < 0.001). Moreover, being pretreatment with naloxone at a dose of 1 mg/kg, the morphine group showed significantly increased in the spike count (p < 0.05).

CONCLUSIONS

Morphine has biphasic effects on PTZ-induced epileptiform activities that way at a low dose has an inhibitory effect, but if the dose is increased, it will intensify the desired event and that the stimulatory effects of morphine appear not to be via opioid receptors.

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.

Solving the Problem of Assessing Synergy and Antagonism for Non-Traditional Dosing Curve Compounds Using the DE/ZI Method: Application to Nrf2 Activators

Multi-drug combination therapy carries significant promise for pharmacological intervention, primarily better efficacy with less toxicity and fewer side effects. However, the field lacks methodology to assess synergistic or antagonistic interactions for drugs with non-traditional dose response curves. Specifically, our goal was to assess small-molecule modulators of antioxidant response element (ARE)-driven gene expression, which is largely regulated by the Nrf2 transcription factor. Known as Nrf2 activators, this class of compounds upregulates a battery of cytoprotective genes and shows significant promise for prevention of numerous chronic diseases. For example, sulforaphane sourced from broccoli sprouts is the subject of over 70 clinical trials. Nrf2 activators generally have non-traditional dose response curves that are hormetic, or U-shaped. We introduce a method based on the principles of Loewe Additivity to assess synergism and antagonism for two compounds in combination. This method, termed Dose-Equivalence/Zero Interaction (DE/ZI), can be used with traditional Hill-slope response curves, and it also can assess interactions for compounds with non-traditional curves, using a nearest-neighbor approach. Using a Monte-Carlo method, DE/ZI generates a measure of synergy or antagonism for each dosing pair with an associated error and p-value, resulting in a 3D response surface. For the assessed Nrf2 activators, sulforaphane and di-tert-butylhydroquinone, this approach revealed synergistic interactions at higher dosing concentrations consistently across data sets and potential antagonistic interactions at lower concentrations. DE/ZI eliminates the need to determine the best fit equation for a given data set and values experimentally-derived results over formulated fits.

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.

Hormesis: A potential strategic approach to the treatment of neurodegenerative disease

This review describes neuroprotective effects mediated by pre- and post-conditioning-induced processes that act via the quantitative features of the hormetic dose response. These lead to the development of acquired resilience that can protect neuronal systems from endogenous and exogenous stresses and insult. Particular attention is directed to issues of dose optimization, inter-individual variation, and potential ways to further study and employ hormetic-based preconditioning approaches in medical and public health efforts to treat and prevent neurodegenerative disease.

Anticonvulsant Activity of Essential Oil From Leaves of Zhumeria majdae (Rech.) in Mice: The Role of GABAA Neurotransmission and the Nitric Oxide Pathway

The essential oil from the leaves of Zhumeria majdae Rech. (ZMEO) has been shown to have several beneficial effects in the clinic. In this work we examined the anticonvulsant activities of ZMEO in an experimental mouse model of seizure and aimed to identify any possible underlying mechanisms. ZMEO (5, 10, 20, and 40 mg/kg intraperitoneally (i.p.)) or diazepam, as the reference anticonvulsant drug (25, 50 and 100 µg/kg i.p.), were administered 60 minutes prior to pentylenetetrazol (PTZ) injection (intravenously (i.v.) or i.p.) and changes in threshold, latency, and frequency of clonic seizure were examined. The PTZ i.p.-induced model of seizure was also applied for examining the protective effects of ZMEO pretreatment against PTZ-induced mortality. In some studies, the anticonvulsant effect of the combination of diazepam and ZMEO was also studied. The protective effects of ZMEO against hindlimb tonic extensions (HLTEs) were also examined by maximal electroshock (MES) seizure testing. The γ-aminobutyric acid (GABA)ergic mechanism and nitric oxide (NO) pathway involvement in anticonvulsant activity of ZMEO were assessed by pretreating animals with flumazenil, Nω -nitro-L-arginine methyl ester (L-NAME), aminoguanidine, and L-arginine in a PTZ-induced model of seizure. Administration of 20 mg/kg ZMEO significantly increased chronic seizure threshold and latency while reducing frequency of convulsions and mortality in the PTZ-induced model. In the doses studied, ZMEO could not protect mice from HLTE and mortality induced by MES. Pretreatment with L-arginine and diazepam potentiated the anticonvulsant effects of ZMEO, whereas pretreatment with L-NAME, aminoguanidine, and flumazenil reversed anticonvulsant activity. The anticonvulsant activity of ZMEO may be mediated in part through a GABAergic mechanism and the NO signaling pathway.

Acute and chronic effects of morphine on Low-Mg2+ ACSF-induced epileptiform activity during infancy in mice hippocampal slices

Interaction of morphine and seizure is complex. Mouse brain hippocampal slices were used to estimate how acute and chronic morphine treatment alters the low-magnesium artificial cerebrospinal fluid (LM-ACSF)-induced seizure activity. Hippocampal slices were taken from the normal and morphine-treated mice. The normal mice received saline while the other group (morphine-treated mice) received morphine daily for 5 consecutive days. Saline/morphine administration was performed subcutaneously (s.c, 0.1 mL) at postnatal days 14-18. Hippocampal slices of all animals were perfused with LM-ACSF followed by different morphine concentrations (0, 10, 100, and 1000 μM) or naloxone (10 μM). Changes in the spike count were considered as indices for quantifying the seizure activity in the slices. In hippocampus of both groups perfused with 10 or 1000 μM morphine, epileptiform activity was suppressed while it was potentiated at 100 μM morphine. The excitatory effect of morphine at 100 μM was stronger in normal mice (acute exposure) than in dependent mice (chronic exposure). Naloxone suppressed the epileptiform activities in both groups. Suppressive effect of naloxone was more significant in morphine-treated mice than in normal mice. The seizure activity in morphine-dependent mice was more labile than that of normal mice. It can be concluded that morphine had a biphasic effect on LM-ACSF-induced epileptiform activities in both groups. The occurrence of seizure was comparable in acute and chronic exposure of morphine but strength of the effect was considerably robust in normal mice. The down regulation of opioid receptors in chronic exposure is likely to be responsible for these differences.

QSAR and Molecular Docking Studies of the Inhibitory Activity of Novel Heterocyclic GABA Analogues over GABA-AT

We have previously reported the synthesis, in vitro and in silico activities of new GABA analogues as inhibitors of the GABA-AT enzyme from Pseudomonas fluorescens, where the nitrogen atom at the γ-position is embedded in heterocyclic scaffolds. With the goal of finding more potent inhibitors, we now report the synthesis of a new set of GABA analogues with a broader variation of heterocyclic scaffolds at the γ-position such as thiazolidines, methyl-substituted piperidines, morpholine and thiomorpholine and determined their inhibitory potential over the GABA-AT enzyme from Pseudomonas fluorescens. These structural modifications led to compound 9b which showed a 73% inhibition against this enzyme. In vivo studies with PTZ-induced seizures on male CD1 mice show that compound 9b has a neuroprotective effect at a 0.50 mmole/kg dose. A QSAR study was carried out to find the molecular descriptors associated with the structural changes in the GABA scaffold to explain their inhibitory activity against GABA-AT. Employing 3D molecular descriptors allowed us to propose the GABA analogues enantiomeric active form. To evaluate the interaction with Pseudomonas fluorescens and human GABA-AT by molecular docking, the constructions of homology models was carried out. From these calculations, 9b showed a strong interaction with both GABA-AT enzymes in agreement with experimental results and the QSAR model, which indicates that bulky ligands tend to be the better inhibitors especially those with a sulfur atom on their structure.

Hormesis: Path and Progression to Significance

This paper tells the story of how hormesis became recognized as a fundamental concept in biology, affecting toxicology, microbiology, medicine, public health, agriculture, and all areas related to enhancing biological performance. This paper assesses how hormesis enhances resilience to normal aging and protects against a broad spectrum of neurodegenerative, cardiovascular, and other diseases, as well as trauma and other threats to health and well-being. This paper also explains the application of hormesis to several neurodegenerative diseases such as Parkinson’s and Huntington’s disease, macrophage polarization and its systematic adaptive protections, and the role of hormesis in enhancing stem cell functioning and medical applications.

Hormesis as a mechanistic approach to understanding herbal treatments in traditional Chinese medicine

Traditional Chinese medicine (TCM) has been long practiced and is becoming ever more widely recognized as providing curative and/or healing treatments for a number of diseases and physiological conditions. This paper posits that herbal medicines used in TCM treatments may act through hormetic dose-response mechanisms. It is proposed that the stimulatory (i.e., low dose) and inhibitory (i.e., high dose) components of the hormetic dose response correspond to respective "regulating" and "curing" aspects of TCM herbal treatments. Specifically, the "regulating" functions promote adaptive or preventive responses, while "curing" treatments alleviate the clinical symptoms. Patterns of hormetic responses are described, and the applicability of these processes to herbal medicines of TCM are explicated. It is noted that a research agenda aimed at elucidating these mechanisms and patterns would be expansive and complex. However, we argue its value, in that hormesis may afford something akin to a Rosetta Stone with which to interpret, translate, and explain TCM herbology in ways that are aligned with biomedical perspectives that could enable a more integrative approach to medicine.

How does hormesis impact biology, toxicology, and medicine?

Hormesis refers to adaptive responses of biological systems to moderate environmental or self-imposed challenges through which the system improves its functionality and/or tolerance to more severe challenges. The past two decades have witnessed an expanding recognition of the concept of hormesis, elucidation of its evolutionary foundations, and underlying cellular and molecular mechanisms, and practical applications to improve quality of life. To better inform future basic and applied research, we organized and re-evaluated recent hormesis-related findings with the intent of incorporating new knowledge of biological mechanisms, and providing fundamental insights into the biological, biomedical and risk assessment implications of hormesis. As the literature on hormesis is expanding rapidly into new areas of basic and applied research, it is important to provide refined conceptualization of hormesis to aid in designing and interpreting future studies. Here, we establish a working compartmentalization of hormesis into ten categories that provide an integrated understanding of the biological meaning and applications of hormesis.

The role of hormesis in the functional performance and protection of neural systems

This paper addresses how hormesis, a biphasic dose response, can protect and affect performance of neural systems. Particular attention is directed to the potential role of hormesis in mitigating age-related neurodegenerative diseases, genetically based neurological diseases, as well as stroke, traumatic brain injury, seizure, and stress-related conditions. The hormetic dose response is of particular significance since it mediates the magnitude and range of neuroprotective processes. Consideration of hormetic dose-response concepts can also enhance the quality of study designs, including sample size/statistical power strategies, selection of treatment groups, dose spacing, and temporal/repeat measures’ features.

Heat shock proteins and hormesis in the diagnosis and treatment of neurodegenerative diseases

Modulation of endogenous cellular defense mechanisms via the vitagene system represents an innovative approach to therapeutic intervention in diseases causing chronic tissue damage, such as in neurodegeneration. The possibility of high-throughoutput screening using proteomic techniques, particularly redox proteomics, provide more comprehensive overview of the interaction of proteins, as well as the interplay among processes involved in neuroprotection. Here by introducing the hormetic dose response concept, the mechanistic foundations and applications to the field of neuroprotection, we discuss the emerging role of heat shock protein as prominent member of vitagene network in neuroprotection and redox proteomics as a tool for investigating redox modulation of stress responsive vitagenes. Hormetic mechanisms are reviewed as possibility of targeted therapeutic manipulation in a cell-, tissue- and/or pathway-specific manner at appropriate points in the neurodegenerative disease process.

What is hormesis and its relevance to healthy aging and longevity?

This paper provides a broad overview of hormesis, a specific type of biphasic dose response, its historical and scientific foundations as well as its biomedical applications, especially with respect to aging. Hormesis is a fundamental component of adaptability, neutralizing many endogenous and environmental challenges by toxic agents, thereby enhancing survival. Hormesis is highly conserved, broadly generalizable, and pleiotrophic, being independent of biological model, endpoint measured, inducing agent, level of biological organization and mechanism. The low dose stimulatory hormetic response has specific characteristics which defines both the quantitative features of biological plasticity and the potential for maximum biological performance, thereby estimating the limits to which numerous medical and pharmacological interventions may affect humans. The substantial degrading of some hormetic processes in the aged may profoundly reduce the capacity to respond effectively to numerous environmental/ischemic and other stressors leading to compromised health, disease and, ultimately, defining the bounds of longevity.

Osteoporosis and alzheimer pathology: Role of cellular stress response and hormetic redox signaling in aging and bone remodeling

Alzheimer’s disease (AD) and osteoporosis are multifactorial progressive degenerative disorders. Increasing evidence shows that osteoporosis and hip fracture are common complication observed in AD patients, although the mechanisms underlying this association remain poorly understood. Reactive oxygen species (ROS) are emerging as intracellular redox signaling molecules involved in the regulation of bone metabolism, including receptor activator of nuclear factor-κB ligand-dependent osteoclast differentiation, but they also have cytotoxic effects that include lipoperoxidation and oxidative damage to proteins and DNA. ROS generation, which is implicated in the regulation of cellular stress response mechanisms, is an integrated, highly regulated, process under control of redox sensitive genes coding for redox proteins called vitagenes. Vitagenes, encoding for proteins such as heat shock proteins (Hsps) Hsp32, Hsp70, the thioredoxin, and the sirtuin protein, represent a systems controlling a complex network of intracellular signaling pathways relevant to life span and involved in the preservation of cellular homeostasis under stress conditions. Consistently, nutritional anti-oxidants have demonstrated their neuroprotective potential through a hormetic-dependent activation of vitagenes. The biological relevance of dose–response affects those strategies pointing to the optimal dosing to patients in the treatment of numerous diseases. Thus, the heat shock response has become an important hormetic target for novel cytoprotective strategies focusing on the pharmacological development of compounds capable of modulating stress response mechanisms. Here we discuss possible signaling mechanisms involved in the activation of vitagenes which, relevant to bone remodeling and through enhancement of cellular stress resistance provide a rationale to limit the deleterious consequences associated to homeostasis disruption with consequent impact on the aging process.

Tanshinone IIA exhibits anticonvulsant activity in zebrafish and mouse seizure models

Danshen or Chinese red sage (Salvia miltiorrhiza, Bunge) is used by traditional Chinese medicine (TCM) practitioners to treat neurological, cardiovascular, and cerebrovascular disorders and is included in some TCM formulations to control epileptic seizures. In this study, acetonic crude extracts of danshen inhibited pentylenetetrazol (PTZ)-induced seizure activity in zebrafish larvae. Subsequent zebrafish bioassay-guided fractionation of the extract resulted in the isolation of four major tanshinones, which suppressed PTZ-induced activity to varying degrees. One of the active tanshinones, tanshinone IIA, also reduced c-fos expression in the brains of PTZ-exposed zebrafish larvae. In rodent seizure models, tanshinone IIA showed anticonvulsive activity in the mouse 6-Hz psychomotor seizure test in a biphasic manner and modified seizure thresholds in a complex manner for the mouse i.v. PTZ seizure assay. Interestingly, tanshinone IIA is used as a prescription drug in China to address cerebral ischemia in patients. Here, we provide the first in vivo evidence demonstrating that tanshinone IIA has anticonvulsant properties as well.

Hormesis: its impact on medicine and health

This article offers a broad assessment of the hormetic dose response and its relevance to biomedical researchers, physicians, the pharmaceutical industry, and public health scientists. This article contains a series of 61 questions followed by relatively brief but referenced responses that provides support for the conclusion that hormesis is a reproducible phenomenon, commonly observed, with a frequency far greater than other dose-response models such as the threshold and linear nonthreshold dose-response models. The article provides a detailed background information on the historical foundations of hormesis, its quantitative features, mechanistic foundations, as well as how hormesis is currently being used within medicine and identifying how this concept could be further applied in the development of new therapeutic advances and in improved public health practices.

Hormesis: why it is important to biogerontologists

This paper offers a broad assessment of the hormetic dose response and its relevance to biogerontology. The paper provides detailed background information on the historical foundations of hormesis, its quantitative features, mechanistic foundations, as well as how the hormesis concept could be further applied in the development of new therapeutic advances in the treatment of age-related diseases. The concept of hormesis has direct application to biogerontology not only affecting the quality of the aging process but also experimental attempts to extend longevity.

Hormesis: improving predictions in the low-dose zone

This chapter explores the historical foundations of hormesis, including the underlying reasons for its marginalization during most of the twentieth century and factors that are contributing to its resurgence and acceptance within the toxicological and pharmacological communities. Special consideration is given to the quantitative features of the hormetic dose response, as well as its capacity for generalization. Based on subsequent comparisons with other leading dose-response models, the hormesis dose response consistently provides more accurate predictions in the below threshold zone. It is expected that the hormetic dose response will become progressively more useful to the fields of toxicology, pharmacology, risk assessment, and the life sciences in general, especially where low-dose effects are of interest.

Hormesis provides a generalized quantitative estimate of biological plasticity

Phenotypic plasticity represents an environmentally-based change in an organism's observable properties. Since biological plasticity is a fundamental adaptive feature, it has been extensively assessed with respect to its quantitative features and genetic foundations, especially within an ecological evolutionary framework. Toxicological investigations on the dose-response continuum (i.e., very broad dose range) that include documented evidence of the hormetic dose response zone (i.e., responses to doses below the toxicological threshold) can be employed to provide a quantitative estimate of phenotypic plasticity. The low dose hormetic stimulation is an adaptive response that reflects an environmentally-induced altered phenotype and provides a quantitative estimate of biological plasticity. Analysis of nearly 8,000 dose responses within the hormesis database indicates that quantitative features of phenotypic plasticity are highly generalizable, being independent of biological model, endpoint measured and chemical/physical stress inducing agent. The magnitude of phenotype changes indicative of plasticity is modest with maximum responses typically being approximately 30-60% greater than control values. The present findings provide the first quantitative estimates of biological plasticity and its capacity for generalization. Summary This article provides the first quantitative estimate of biological plasticity that may be generalized across plant, microbial, animal systems, and across all levels of biological organization. The quantitative features of plasticity are described by the hormesis dose response model. These findings have important biological, biomedical and evolutionary implications.

Cellular stress responses, the hormesis paradigm, and vitagenes: novel targets for therapeutic intervention in neurodegenerative disorders

Despite the capacity of chaperones and other homeostatic components to restore folding equilibrium, cells appear poorly adapted for chronic oxidative stress that increases in cancer and in metabolic and neurodegenerative diseases. Modulation of endogenous cellular defense mechanisms represents an innovative approach to therapeutic intervention in diseases causing chronic tissue damage, such as in neurodegeneration. This article introduces the concept of hormesis and its applications to the field of neuroprotection. It is argued that the hormetic dose response provides the central underpinning of neuroprotective responses, providing a framework for explaining the common quantitative features of their dose-response relationships, their mechanistic foundations, and their relationship to the concept of biological plasticity, as well as providing a key insight for improving the accuracy of the therapeutic dose of pharmaceutical agents within the highly heterogeneous human population. This article describes in mechanistic detail how hormetic dose responses are mediated for endogenous cellular defense pathways, including sirtuin and Nrf2 and related pathways that integrate adaptive stress responses in the prevention of neurodegenerative diseases. Particular attention is given to the emerging role of nitric oxide, carbon monoxide, and hydrogen sulfide gases in hormetic-based neuroprotection and their relationship to membrane radical dynamics and mitochondrial redox signaling.

Hormesis is central to toxicology, pharmacology and risk assessment

This paper summarizes numerous conceptual and experimental advances over the past two decades in the study of hormesis. Hormesis is now generally accepted as a real and reproducible biological phenomenon, being highly generalized and independent of biological model, endpoint measured and chemical class/physical stressor. The quantitative features of the hormetic dose response are generally highly consistent, regardless of the model and mechanism, and represent a quantitative index of biological plasticity at multiple levels of biological organization. The hormetic dose-response model has been demonstrated to make far more accurate predictions of responses in low dose zones than either the threshold or linear at low dose models. Numerous therapeutic agents widely used by humans are based on the hormetic dose response and its low dose stimulatory characteristics. It is expected that as low dose responses come to dominate toxicological research that risk assessment practices will incorporate hormetic concepts in the standard setting process.

Hormesis: a conversation with a critic

OBJECTIVE

In this commentary I respond to points raised in the commentary by Mushak [Ad hoc and fast forward: the science and control of hormesis growth and development. Environ Health Perspect 117:1333-1338 (2009)], which principally concerns studies by me and my colleagues concerning the frequency of hormesis in toxicology.

DISCUSSION

In this commentary I demonstrate that Mushak's analysis contains critical statistical errors and misunderstandings of statistical concepts that invalidate its conclusions concerning the frequency of hormesis in the toxicologic literature.

CONCLUSIONS

In his commentary Mushak offers no significant new conceptual insights, and his key technical criticisms of hormesis frequency findings are unfounded.

Hormesis and medicine

Evidence is presented which supports the conclusion that the hormetic dose-response model is the most common and fundamental in the biological and biomedical sciences, being highly generalizable across biological model, endpoint measured and chemical class and physical agent. The paper provides a broad spectrum of applications of the hormesis concept for clinical medicine including anxiety, seizure, memory, stroke, cancer chemotherapy, dermatological processes such as hair growth, osteoporosis, ocular diseases, including retinal detachment, statin effects on cardiovascular function and tumour development, benign prostate enlargement, male sexual behaviours/dysfunctions, and prion diseases.