Hormetic Dose Response Research Articles

Protection against neurodegeneration with low-dose methylene blue and near-infrared light.

Neurons are metabolically protected against degeneration using low-level methylene blue and near-infrared light interventions. Both of these novel interventions act by a cellular mechanism involving enhancement of the electron transport chain in mitochondria, which promotes energy metabolism and neuronal survival (Gonzalez-Lima et al., 2014). Methylene blue preferentially enters neuronal mitochondria after systemic administration, and at low-doses forms an electron cycling redox complex that donates electrons to the mitochondrial electron transport chain. Low-level near-infrared light applied transcranially delivers photons to cortical neurons that are accepted by cytochrome oxidase, which causes increased cell respiration and cerebral blood flow. Breakthrough in vivo studies with these interventions suggest that targeting mitochondrial respiration may be beneficial for protection against different types of neurodegenerative disorders. The purpose of this paper is to provide an update on the cellular mechanisms mediating the neuroprotective effects of low doses of methylene blue and near-infrared light, and to argue that the neurotherapeutic benefits of these two different interventions share the same cellular mechanism of action based on stimulation of mitochondrial respiration. Presented first is the explanation of the biochemical redox action of low-dose methylene as an electron cycler on the mitochondrial electron transport. Presented second is the explanation of the biophysical action of near-infrared light as a photon donor to cytochrome oxidase that also serves to stimulate mitochondrial electron transport. We finish with a comparison of these two interventions and how they share a common cellular mechanism with similar properties such as energy transfer, low-dose hormetic dose-responses, and enhanced capacity for oxidative metabolic energy production, which serve to protect nervous tissue from degeneration.

Ecotoxicity of two organophosphate pesticides chlorpyrifos and dichlorvos on non-targeting cyanobacteria Microcystis wesenbergii.

Organophosphate pesticides (OPs), as a replacement for the organochlorine pesticides, are generally considered non-toxic to plants and algae. Chlorpyrifos and dichlorvos are two OPs used for pest control all over the world. In this study, the dose-response of cyanobacteria Microcystis wesenbergii on OPs exposure and the stimulating effect of OPs with and without phosphorus source were investigated. The results showed that high concentrations of chlorpyrifos and dichlorvos caused significant decrease of chlorophyll a content. The median inhibitory concentrations (EC50) of chlorpyrifos and dichlorvos at 96 h were 15.40 and 261.16 μmol L(-1), respectively. Growth of M. wesenbergii under low concentration of OPs (ranged from 1/10,000 to 1/20 EC50), was increased by 35.85 % (chlorpyrifos) and 41.83 % (dichlorvos) at 120 h, respectively. Correspondingly, the highest enhancement on the maximum quantum yield (F v/F m) was 4.20 % (24 h) and 9.70 % (48 h), respectively. Chlorophyll fluorescence kinetics, known as O-J-I-P transients, showed significant enhancements in the O-J, J-I, and I-P transients under low concentrations of dichlorvos at 144 h, while enhancements of chlorophyll fluorescence kinetics induced by low concentrations of chlorpyrifos were only observed in the J-I transient at 144 h. Significant decreases of chlorophyll content, F v/F m and O-J-I-P transients with OPs as sole phosphorus source were found when they were compared with inorganic phosphate treatments. The results demonstrated an evidently hormetic dose-response of M. wesenbergii to both chlorpyrifos and dichlorvos, where high dose (far beyond environmental concentrations) exposure caused growth inhibition and low dose exposure induced enhancement on physiological processes. The stimulating effect of two OPs on growth of M. wesenbergii was negligible under phosphate limitation.

Statistical modeling of the hormetic dose zone and the toxic potency completes the quantitative description of hormetic dose responses.

Quantifying the characteristics of hormesis provides valuable insights into this low-dose phenomenon and helps to display and capture its variability. A prerequisite to do so is a statistical procedure allowing quantification of general hormetic features, namely the maximum stimulatory response, the dose range of hormesis, and the distance from the maximum stimulation to the dose where hormesis disappears. Applying extensions of a hormetic dose-response model that is well-established in plant biology provides a direct estimation of several quantities, except the hormetic dose range. Another dose range that is difficult to model directly is the distance between the dose where hormesis disappears and the dose giving 50% inhibition, known as toxic potency. The present study presents 2 further model extensions allowing for a direct quantification of the hormetic dose range and the toxic potency. Based on this, a 4-step mathematical modeling approach is demonstrated to quantify various dose-response quantities, to compare these quantities among treatments, and to interrelate hormesis features. Practical challenges are exemplified, and possible remedies are identified. The software code to perform the analysis is provided as Supplemental Data to simplify adoption of the modeling procedure. Because numerous patterns of hormesis are observed in various sciences, it is clear that the proposed approach cannot cope with all patterns; however, it should be possible to analyze a great range of hormesis patterns.

Hormesis: principles and applications

Hormesis has emerged as a central concept in biological and biomedical sciences with significant implications for clinical medicine and environmental risk assessment. This paper assesses the historical foundations of the dose-response including the threshold, linear and hormetic models, the occurrence and frequency of the hormetic dose response in the pharmacological and toxicological literature, its quantitative and temporal features, and underlying mechanistic bases. Based upon this integrative foundation the application of hormesis to the process of risk assessment for non-carcinogens and carcinogens is explored.

Hormesis within a mechanistic context

This paper provides an assessment of the mechanistic foundations of hormesis and how such understandings evolved over the course of the past century. Particular emphasis is placed on recent developments particularly with respect to receptor-based and cell signaling-based pathways. Of particular importance is that the quantitative feature of the hormetic dose response are independent of mechanism.

Aging-modulating treatments: from reductionism to a system-oriented perspective.

The delay of aging and healthy life extension is a primary concern of modern gerontological research. Based on theoretical assumptions and empirical findings, a number of bioactive agents have been proposed as promising “anti-aging” (geroprotective) preparations (de Magalhaes et al., 2012; Kennedy and Pennypacker, 2014). Usually, the substance is considered to have aging-modulating activity if its efficiency can be confirmed both in vitro and in vivo. In the first step of screening, a hypothetical geroprotective compound (e.g., antioxidant known to play a key role in ROS scavenging) is examined in in vitro models. If its effectiveness is confirmed, then its aging-modulating properties are studied in experimental in vivo models. In the case where supplementation of experimental animals with this agent causes life extension, it advertised as anti-aging drug. A logic discrepancy, however, can be generated between these two steps. Indeed, even if some substance is highly effective in in vitro model due to influencing a specific age-related pathway, its life-extending effects in animal models might be caused by unspecific (hormetic) mechanisms. Hormetic responses are commonly referred to as stimulatory effects occurring in response to low levels of exposure to stressors or agents that are harmful at high levels of exposure. The prevailing hypothesis explaining the hormetic phenomenon is that a low dose of a toxic agent induces damage; following this damage, a repair response is initiated which result in a slight overcompensation to the disruption of homeostasis, i.e., a general response of the organism (Calabrese, 2013). According to this hypothesis, various mild stresses and low-dose pharmacological treatments may cause rather similar beneficial effects because these effects are not mediated by specific receptors. There is a large corpus of data demonstrating that hormesis is implicated in health and disease across various species including human beings (Rattan and Le Bourg, 2014). Longevity hormesis was repeatedly obtained for a number of obviously harmful substances including herbicides, pesticides, heavy metals, and hydrocarbons (Neafsey, 1990). The hormetic model of dose response is usually described as U-shaped curve ranging from impairment at levels of deficient intake, to optimal function at intermediate levels, and to toxicity at excessive intake levels (Calabrese, 2013). All prospective aging-modulating agents are essential nutrients necessary to support health and well-being. These dietary components including minerals, trace elements, vitamins and antioxidants, however, similarly to hormetic compounds (“hormetins”) all exhibit toxic effects at excess levels, i.e., they show typical hormetic dose response (Rattan, 2008). Indeed, while the moderate daily levels of vitamins and minerals are both required and beneficial, their excessive dietary levels are known to cause hypervitaminosis, tissue mineralization, or electrolyte imbalance (Hayes, 2007). The excessive intake of antioxidants and hormones is known to destroy delicate control mechanisms of homeodynamics, and it seems therefore unlikely that they have a long-term beneficial impact (Goto, 2004). Furthermore, both presumably agingmodulating effects and hormetic effects do not preclude the coexistence of toxicity and other adverse outcomes. The predominance of beneficial (life-extending) or deleterious effects may vary not only with dose but also with species, gender, age, stage of life, disease or disability (Minois, 2000). In some cases, life extension caused by both hormetins and geroprotectors may be accompanied by side effects such as impairment of reproductive and immune functions, as well as stress resistance (Matsagas et al., 2009; Saul et al., 2013; McClure et al., 2014). In addition, pharmaceutical interventions can act as caloric restriction (CR) mimetics due to the suppression of the appetite, and their life-extending effects may be caused, at least partially, by the CR-inducing hormetic response (Masoro, 2007). Given all these consideration, it can be concluded that similarity may exist in the mode of action between hormetins and geroprotectors. Currently, however, these are no valid criteria to distinguish mechanistic pathways between them. Such criteria were first proposed and efforts were made to validate them as early as in the 60–70 s of the last century in works of George A. Sacher which distinguished the life-extending effects of substances acting by a “proper action” (a specific role of these agents in reducing the accumulation of age-associated lesions or protecting against age-related disorders) from the hormetic (non-specific) effects (Sacher, 1977). According to this point of view, a hormetic response is a function of the state of an organism, rather than a kind

Dose response biology of resveratrol in obesity.

Obesity is a major health problem throughout the world, and it is increasing both in prevalence and severity. Pharmaceutical approaches developed for the treatment of obesity, despite short-term benefits, often are associated with rebound weight gain after the cessation of drug use and serious side effects deriving from the medication can occur. Resveratrol has been well recognized as an anti-obesity substance for its lipid-lowering function as well as calorie-restriction effect. This polyphenol induces hormetic dose responses in a wide range of biological models, affecting numerous endpoints of biomedical and therapeutic significance. From an hormetic standpoint, we will discuss the potential relevance of resveratrol in the management of obesity and related comorbid conditions, emphasizing its ability to control simultaneously various pathological mechanisms associated with obesity.

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.

The effect of experimental exposure to low doses of zearalenone on uterine histology and morphometry in prepubertal bitches

The experiment involved 30 clinically healthy prepubertal bitches aged approximately 70 days with an estimated initial body weight (BW) of 8 kg. The animals were randomly divided into two experimental groups (EI and EII) and a control group of 10 animals each. Group EI was administered 50 μg zearalenone (ZEN)/kg BW per os for 42 days, group EII received 75 μg zearalenone/kg BW per os for 42 days, and the control group was administered placebo per os for 42 days. The bitches were hysterectomized at the end of treatment, and samples of uterine tissue were collected for histological and morphometric analyses. The results of the study indicate that exposure to very low doses of ZEN (100% and 150% of the NOAEL) causes simple glandular hyperplasia of the endometrium accompanied by adenogenesis, angiogenesis, and vasodilatation with the related consequences. The noted changes were more pronounced in group EI and less visible in group EII in comparison with group C, which could be indicative of a hormetic dose response.

Hormesis: a fundamental concept in biology

This paper assesses the hormesis dose response concept, including its historical foundations, frequency, generality, quantitative features, mechanistic basis and biomedical, pharmaceutical and environmental health implications. The hormetic dose response is highly generalizable, being independent of biology model (i.e. common from plants to humans), level of biological organization (i.e. cell, organ and organism), endpoint, inducing agent and mechanism, providing the first general and quantitative description of plasticity. The hormetic dose response describes the limits to which integrative endpoints (e.g. cell proliferation, cell migration, growth patterns, tissue repair, aging processes, complex behaviors such as anxiety, learning, memory, and stress, preconditioning responses, and numerous adaptive responses) can be modulated (i.e., enhanced or diminished) by pharmaceutical, chemical and physical means. Thus, the hormesis concept is a fundamental concept in biology with a wide range of biological implications and biomedical applications.

Neurological and psychological applications of transcranial lasers and LEDs

Transcranial brain stimulation with low-level light/laser therapy (LLLT) is the use of directional low-power and high-fluency monochromatic or quasimonochromatic light from lasers or LEDs in the red-to-near-infrared wavelengths to modulate a neurobiological function or induce a neurotherapeutic effect in a nondestructive and non-thermal manner. The mechanism of action of LLLT is based on photon energy absorption by cytochrome oxidase, the terminal enzyme in the mitochondrial respiratory chain. Cytochrome oxidase has a key role in neuronal physiology, as it serves as an interface between oxidative energy metabolism and cell survival signaling pathways. Cytochrome oxidase is an ideal target for cognitive enhancement, as its expression reflects the changes in metabolic capacity underlying higher-order brain functions. This review provides an update on new findings on the neurotherapeutic applications of LLLT. The photochemical mechanisms supporting its cognitive-enhancing and brain-stimulatory effects in animal models and humans are discussed. LLLT is a potential non-invasive treatment for cognitive impairment and other deficits associated with chronic neurological conditions, such as large vessel and lacunar hypoperfusion or neurodegeneration. Brain photobiomodulation with LLLT is paralleled by pharmacological effects of low-dose USP methylene blue, a non-photic electron donor with the ability to stimulate cytochrome oxidase activity, redox and free radical processes. Both interventions provide neuroprotection and cognitive enhancement by facilitating mitochondrial respiration, with hormetic dose–response effects and brain region activational specificity. This evidence supports enhancement of mitochondrial respiratory function as a generalizable therapeutic principle relevant to highly adaptable systems that are exquisitely sensitive to energy availability such as the nervous system.

Stress responses, vitagenes and hormesis as critical determinants in aging and longevity: Mitochondria as a "chi".

Understanding mechanisms of aging and determinants of life span will help to reduce age-related morbidity and facilitate healthy aging. Average lifespan has increased over the last centuries, as a consequence of medical and environmental factors, but maximal life span remains unchanged. Extension of maximal life span is currently possible in animal models with measures such as genetic manipulations and caloric restriction (CR). CR appears to prolong life by reducing reactive oxygen species (ROS)-mediated oxidative damage. But ROS formation, which is positively implicated in cellular stress response mechanisms, is a highly regulated process controlled by a complex network of intracellular signaling pathways. By sensing the intracellular nutrient and energy status, the functional state of mitochondria, and the concentration of ROS produced in mitochondria, the longevity network regulates life span across species by coordinating information flow along its convergent, divergent and multiply branched signaling pathways, including vitagenes which are genes involved in preserving cellular homeostasis during stressful conditions. Vitagenes encode for heat shock proteins (Hsp) Hsp32, Hsp70, the thioredoxin and the sirtuin protein systems. Dietary antioxidants, have recently been demonstrated to be neuroprotective through the activation of hormetic pathways, including vitagenes. The hormetic dose–response, challenges long-standing beliefs about the nature of the dose–response in a lowdose zone, having the potential to affect significantly the design of pre-clinical studies and clinical trials as well as strategies for optimal patient dosing in the treatment of numerous diseases. Given the broad cytoprotective properties of the heat shock response there is now strong interest in discovering and developing pharmacological agents capable of inducing stress responses. Here we focus on possible signaling mechanisms involved in the activation of vitagenes resulting in enhanced defense against energy and stress resistance homeostasis dysiruption with consequent impact on longevity processes.

Historical foundations of wound healing and its potential for acceleration: dose‐response considerations

This paper provides a detailed historical assessment of the origin and developmental progress of the concept of wound healing and its attempted acceleration from its start in the beginning of the 20th century to approximately 1960. Emphasis is placed on the development of cell culture in the assessment of wound healing and in attempts to validate experimental findings via clinical research. Of particular interest were the observations that wound healing could be accelerated in the 30-50% range with the dose response displaying biphasic characteristics consistent with the hormesis dose-response model. Such findings set the stage for the hormetic dose-response revolution that is occurring within the biological and biomedical sciences, including wound healing, whereby considerable research now supports the capacity for endogenous and exogenous agents to accelerate the process of wound healing and its functional performance.

Food safety and security and the dose-response

Getting the dose-response right is a critical component in the assessment of chemical food safety. Being able to validate dose-response model predictions in the low-dose zone would be a critical aspect of the assurances that correct decisions about food safety and security are made. The present paper examines the history of the threshold dose-response model and how it became incorporated into governmental regulatory and risk assessment activities, including those affecting chemical food safety. The present analysis reveals that the major risk assessment models used by international regulatory agencies, such as the threshold dose-response model, were never validated prior to their acceptance and use by international regulatory agencies. Furthermore, once they were tested both the threshold and linear dose-response models failed to make accurate predictions in the low-dose zone. The only model providing accurate predictions in the low dose zone was the hormetic dose-response, a model not used by regulatory agencies. The present analysis raises important new questions for the risk assessment process in general and that of chemical food security in particular.

Novel approach to predicting hormetic effects of antibiotic mixtures on Vibrio fischeri

The determination of the hormetic effects of a mixture is quite difficult because of the moderate simulation and the complexity of measurement in low doses. In the present study, two typical models for mixture toxicity prediction, concentration additive (CA) and independent action (IA), were used to predict the hormetic effects of mixtures. The predictive power of those models was validated by the hormetic effects (24-h exposure) of antibiotic’s binary mixtures to Vibrio fischeri. The results showed that CA and IA were unable to predict the hormetic dose-response of mixture, especially those of the interactive mixtures. As an alternative, a novel model, which was named as “six-point” and developed based on the quantitative features in the determined dose-response curve and on the Quantitative Structure Activity Relationships (QSARs) approach, was proposed for predicting the hormetic effects of mixtures in low dose. The results indicated that the “six-point” model can accurately predict the mixture hormetic effects in low dose, not only for non-interactive mixtures but also for interactive mixtures. Therefore, the “six-point” model is a powerful tool to predict the mixture hormetic effects at low dose, and may offer an important approach in the environment risk assessment of mixtures.

Hormesis

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.

Intermittent Hypoxia-Induced Renal Antioxidants and Oxidative Damage in Male Mice: Hormetic dose Response

Obstructive sleep apnea causes cardiovascular disease via chronic intermittent hypoxia (IH), which may be related to oxidative stress. Nuclear factor-erythroid 2-related factor 2 (Nrf2) is an important cellular defense mechanism against oxidative stress by regulating its down-stream multiple antioxidants. The present study was to define whether IH can induce renal pathogenic damage and if so, whether Nrf2 and its down-stream antioxidants are involved in IH-induced pathogenic changes. Mice were culled for exposure to intermittent air as control or IH that consisted of 20.9% O2/ 8% O2 FIO2 alternation cycles (30 episodes per h) with 20 seconds at the nadir FIO2 for 12 h a day during daylight. Short-term IH exposure (3 - 7 days) induced significant increases in renal inflammatory response and antioxidant levels along with a reduction of the spontaneous content of malondialdehyde while long-term IH exposure (8 weeks) induced a significant decrease of antioxidant levels and significant increases of renal inflammation, oxidative damage, cell death, and fibrosis. This study suggests that IH induces a hormetic response, i.e.: short-term IH exposure is able to induce a protective response to protect the kidney from oxidative damage while long-term IH exposure is able to induce a damage effect on the kidney.

Model of Hormesis and Its Toxicity Mechanism Based on Quorum Sensing: A Case Study on the Toxicity of Sulfonamides to Photobacterium phosphoreum

During the past two decades, the phenomenon of hormesis has gained increasing recognition in environmental and toxicological communities. However, the mechanistic understanding of hormesis, to date, is extremely limited. Herein is proposed a novel parametric model with a mechanistic basis and two model-based parameters for hormesis that was successfully applied to the hormetic dose-response observed in the chronic toxicity of sulfonamides on Photobacterium phosphoreum. On the basis of the methods of molecular docking and quantitative structure-activity relationships (QSARs), we proposed a mechanistic hypothesis for hormesis that introduces for the first time the concept of quorum sensing in toxicological studies and explains the mechanism at the level of the receptors. The mechanistic hypothesis stated that (1) specific target binding like interaction with LuxR may contribute to transcriptional activation leading to enhanced luciferase activity at low dose exposure of sulfonamides, and (2) as the dose of sulfonamides increases, more sulfonamides competitively bind to dihydropteroate synthase, which inhibit the biosynthesis of folic acid and thus provoke toxicity. This mechanistic hypothesis, which explains both the dose-dependent and time-dependent features of hormesis, could give new insight into the mechanistic study of hormesis.

A Method to Evaluate Hormesis in Nanoparticle Dose-Responses

The term hormesis describes a dose-response relationship that is characterized by a response that is opposite above and below the toxicological or pharmacological threshold. Previous reports have shown that this relationship is ubiquitous in the response of pharmaceuticals, metals, organic chemicals, radiation, and physical stressor agents. Recent reports have also indicated that certain nanoparticles (NPs) may also exhibit a hormetic dose-response. We describe the application of three previously described methods to quantify the magnitude of the hormetic biphasic dose-responses in nanotoxicology studies. This methodology is useful in screening assays that attempt to parse the observed toxicological dose-response data into categories based on the magnitude of hormesis in the evaluation of NPs. For example, these methods may be used to quickly identify NP induced hormetic responses that are either desirably enhanced (e.g., neuronal cell viability) or undesirably stimulated (e.g., low dose stimulation of tumor cells).

Behavioral effects of taurine pretreatment in zebrafish acutely exposed to ethanol

Taurine (TAU) is an amino sulfonic acid that plays protective roles against neurochemical impairments induced by ethanol (EtOH). Mounting evidence shows the applicability of zebrafish for evaluating locomotor parameters and anxiety-like behavioral phenotypes after EtOH exposure in a large scale manner. In this study, we assess the effects of TAU pretreatment on the behavior of zebrafish in the open tank after acute 1% EtOH (v/v) exposure (20 and 60 min of duration) and on brain alcohol contents. The exposure for 20 min exerted significant anxiolytic effects, which were prevented by 42, 150, and 400 mg/L TAU. Conversely, the 60-min condition induced depressant/sedative effects, in which the changes on vertical activity were associated to modifications on the exploratory profile. Although all TAU concentrations kept locomotor parameters at basal levels, 150 mg/L TAU, did not prevent the impairment on vertical activity of EtOH[60]. Despite the higher brain EtOH content detected in the 60-min exposure, 42, 150, and 400 mg/L TAU attenuated the increase of alcohol content in EtOH[60] group. In conclusion, our data suggest that both protocols of acute EtOH exposure induce significant changes in the spatio-temporal behavior of zebrafish and that TAU may exert a preventive role by antagonizing the effects induced by EtOH possibly due to its neuromodulatory role and also by decreasing brain EtOH levels. The hormetic dose-response of TAU on vertical exploration suggests a complex interaction between TAU and EtOH in the central nervous system.