Biphasic Dose-response Relationships Research Articles

Modeling hormesis using multivariate nonlinear regression in plant biology: A comprehensive approach to understanding dose-response relationships

For over a century, ecotoxicological studies have reported the occurrence of hormesis as a significant phenomenon in many areas of science. In plant biology, hormesis research focuses on measuring morphological, physiological, biochemical, and productivity changes in plants exposed to low doses of herbicides. These studies involve multiple features that are often correlated. However, the multivariate aspect and interdependencies among components of a plant system are not considered in the adopted modeling framework. Therefore, a multivariate nonlinear modeling approach for hormesis is proposed, where information regarding correlations among response variables is taken into account through a variance-covariance matrix obtained from univariate residuals. The proposed methodology is evaluated through a Monte Carlo simulation study and an application to experimental data from safflower (Carthamus tinctorius L.) cultivation. In the simulation study, the multivariate model outperformed the univariate models, exhibiting higher precision, lower bias, and greater accuracy in parameter estimation. These results were also confirmed in the analysis of the experimental data. Using the delta method, mean doses of interest can be derived along with their associated standard errors. This is the first study to address hormesis in a multivariate context, allowing for a better understanding of the biphasic dose-response relationships by considering the interrelationships among various measured characteristics in the plant system, leading to more precise parameter estimates.

English

Hormesis is a biphasic dose (concentration)-response phenomenon characterized by low dose stimulatory and high dose inhibitory effects exerted by stressors on living organisms. Recently, there has been increased interest in the phenomenon and statistical models for its exploration in toxicological studies. The bilogistic model of Beckon et al. is one of such models for modeling biphasic dose-response relationships in toxicological studies. However, there is no explicit formula for the estimation of effective doses (EDK) with the model. In this study, a simple general approach was suggested to reparameterize the model, leading to a range of mathematical models for determination of effective doses at both stimulatory and inhibitory ranges in inverted U-shaped hormetic dose-response relationships. The reparameterized models were tested on experimental data from three different in vitro experimental systems obtained from literature and our experiment. They were successfully applied to test for significance of hormesis and estimate effective doses and their statistical properties. In addition, reparameterization of the model for a particular effective dose (EDK) did not affect estimation of other parameters (such as x1, x2, β1, β2 and M). The reparameterized models provided useful tools for adequate exploration of the tested hormetic dose-response relationships. The extended models could hopefully be versatile in characterization of variable hormetic dose response relationships in many toxicological disciplines.   Key words: Toxicity, hormesis, hormesis quantities, model extension, concentration-responses.

Estimating the range of the maximum hormetic stimulatory response

An ever-expanding hormetic database (HDB) was used to demonstrate that the median maximal hormetic stimulatory response (MHSR) of biphasic dose-response relationships increases in value with an increase in the number of stimulatory doses/concentrations that are administered below the estimated threshold/ZEP (zero equivalent point – i.e., the dose where the response crosses the control group value). With only one dose or concentration administered below the ZEP, the median MHSR for microbes (in vitro), animals (in vitro and in vivo), and plants (in vitro and in vivo) ranged between 120% and 125% of the control response. However, when individual agents having at least six doses below the ZEP were mined from the HDB (and a median MHSR then determined), the median MHSR increased to 160–190%. This progressive increase in the MHSR appears to be due to several factors, including (i) the enhanced capacity of additional doses in the stimulatory hormetic zone to better estimate the response optima, and (ii) enhanced variability due to the presence of more doses in the stimulatory zone. This study offers a novel perspective for improving research protocols, unraveling the limits of biological plasticity, understanding low-level stress biology, advancing human and ecological health, and enhancing human performance.

Hormesis mediates dose-sensitive shifts in macrophage activation patterns.

The activation or polarization of macrophages to pro- or anti-inflammatory states evolved as an adaptation to protect against a spectrum of biological threats. Such an adaptation engages pro-oxidative mechanisms and enables macrophages to neutralize and kill threatening organisms (e.g., viruses, bacteria, mold), limit cancerous growths, and enhance recovery and repair processes. The present study demonstrates that (1) many diverse pharmacological, chemical and physical agents can mediate a dose/concentration-dependent shift between pro- and anti-inflammatory activation states, and (2) these shifts in activation states display biphasic dose-response relationships that are characteristic of hormesis. This study also reveals that preconditioning-another form of hormesis-similarly mediates tissue protection by the polarization of macrophages, but in this case, towards an anti-inflammatory phenotype. This assessment supports the generalizability and significance of hormesis in biology, medicine, and public health and further extends it to encompass the hormetic activation of macrophages.

Predicting the effect of ozone on vegetation via linear non-threshold (LNT), threshold and hormetic dose-response models

The nature of the dose-response relationship in the low dose zone and how this concept may be used by regulatory agencies for science-based policy guidance and risk assessment practices are addressed here by using the effects of surface ozone (O3) on plants as a key example for dynamic ecosystems sustainability. This paper evaluates the current use of the linear non-threshold (LNT) dose-response model for O3. The LNT model has been typically applied in limited field studies which measured damage from high exposures, and used to estimate responses to lower concentrations. This risk assessment strategy ignores the possibility of biological acclimation to low doses of stressor agents. The upregulation of adaptive responses by low O3 concentrations typically yields pleiotropic responses, with some induced endpoints displaying hormetic-like biphasic dose-response relationships. Such observations recognize the need for risk assessment flexibility depending upon the endpoints measured, background responses, as well as possible dose-time compensatory responses. Regulatory modeling strategies would be significantly improved by the adoption of the hormetic dose response as a formal/routine risk assessment option based on its substantial support within the literature, capacity to describe the entire dose-response continuum, documented explanatory dose-dependent mechanisms, and flexibility to default to a threshold feature when background responses preclude application of biphasic dose responses. CapsuleThe processes of ozone hazard and risk assessment can be enhanced by incorporating hormesis into their principles and practices.

Low-dose effects of bisphenol A on mammary gland development in rats.

Bisphenol A (BPA) is widely used in food contact materials, toys, and other products. Several studies have indicated that effects observed at doses near human exposure levels may not be observed at higher doses. Many studies have shown effects on mammary glands at low doses of BPA, however, because of small number of animals or few doses investigated these data have not been used by EFSA as point of departure for the newly assessed tolerable daily intake (TDI). We performed a study with perinatal exposure to BPA (0, 0.025, 0.25, 5, and 50mg/kg bw/day) in rats (n=22 mated/group). One of the aims was to perform a study robust enough to contribute to the risk assessment of BPA and to elucidate possible biphasic dose-response relationships. We investigated mammary gland effects in the offspring at 22, 100, and 400days of age. Male offspring showed increased mammary outgrowth on pup day (PD) 22 at 0.025mg/kg BPA, indicating an increased mammary development at this low dose only. Increased prevalence of intraductal hyperplasia was observed in BPA females exposed to 0.25mg/kg at PD 400, but not at PD 100, and not at higher or lower doses. The present findings support data from the published literature showing that perinatal exposure to BPA can induce increased mammary growth and proliferative lesions in rodents. Our results indicate that low-dose exposure to BPA can affect mammary gland development in male and female rats, although higher doses show a different pattern of effects. The observed intraductal hyperplasia in female rats could be associated with an increased risk for developing hyperplastic lesions, which are parallels to early signs of breast neoplasia in women. Collectively, current knowledge on effects of BPA on mammary gland at low doses indicates that highly exposed humans may not be sufficiently protected.

Hormetic effect induced by depleted uranium in zebrafish embryos

The present work studied the hormetic effect induced by uranium (U) in embryos of zebrafish (Danio rerio) using apoptosis as the biological endpoint. Hormetic effect is characterized by biphasic dose-response relationships showing a low-dose stimulation and a high-dose inhibition. Embryos were dechorionated at 4h post fertilization (hpf), and were then exposed to 10 or 100μg/l depleted uranium (DU) in uranyl acetate solutions from 5 to 6 hpf. For exposures to 10μg/l DU, the amounts of apoptotic signals in the embryos were significantly increased at 20 hpf but were significantly decreased at 24 hpf, which demonstrated the presence of U-induced hormesis. For exposures to 100μg/l DU, the amounts of apoptotic signals in the embryos were significantly increased at 20, 24 and 30 hpf. Hormetic effect was not shown but its occurrence between 30 and 48 hpf could not be ruled out. In conclusion, hormetic effect could be induced in zebrafish embryos in a concentration- and time-dependent manner.

Comparative evaluation of genotoxicity induced by nitrofurazone in two ciliated protozoa by detecting DNA strand breaks and DNA–protein crosslinks

Although organism-specific factors related to individual indicator organisms have hampered the use of bioassays for the evaluation of environmental risk in practice, the importance of understanding organism-specific factors when selecting model organisms has also not yet been fully recognized. In this work, genotoxicity was evaluated in the ciliated protozoa, Euplotes vannus and Pseudokeronopsis rubra, when exposed to graded doses of nitrofurazone for several discrete durations. Genotoxicity was expressed based on the LD50 and was determined by assessing DNA strand breaks (through alkaline comet assay) and DNA–protein crosslinks (DPCs), by means of a KCl–SDS precipitation assay. It was found that E. vannus generally had lower LD50's than P. rubra (P<0.05), and that the LD50 values decreased in both ciliates as the exposure durations increased. Compared to the control groups, the nitrofurazone treated E. vannus generally produced more DNA strand breaks (P<0.05), but for DPCs (P>0.05). The relationship between these parameters was reversed in the case of P. rubra. Biphasic dose–response relationships were generally detected between nitrofurazone and genotoxicity parameters, however, parameters for DNA strand breaks presented significantly positive correlations between each other (P<0.05), but showed nearly no significant correlations with DPC induction. In brief, our findings confirmed nitrofurazone-induced genotoxicity and the important role of organism-specific factors in the selection of model organisms from ciliated protozoa for environmental monitoring and risk assessment in aquaculture.

Hormetic Effect Induced by Alpha-Particle-Induced Stress Communicated In Vivo between Zebrafish Embryos

We report data showing that embryos of the zebrafish, Danio rerio, at 1.5 h post fertilization (hpf) subjected to a low-dose alpha-particle irradiation can release a stress signal into the water, which can be communicated to unirradiated bystander zebrafish embryos sharing the same water medium to induce a hormetic effect in the bystander embryos. Hormetic responses are characterized as biphasic dose-response relationships exhibiting a low-dose stimulation and a high-dose inhibition. The effects on the whole embryos were studied through quantification of apoptotic signals at 24 hpf through staining with the vital dye acridine orange, followed by counting the stained cells under a microscope. The results show that, for low alpha-particle dose, the number of apoptotic signals decreases in the irradiated embryos and also in the unirradiated bystander embryos having partnered with the irradiated embryos. These suggested that alpha-particle-irradiated zebrafish embryos could release a stress signal into the water, which could be communicated to unirradiated bystander zebrafish embryos sharing the same water medium to induce a hormetic effect in the bystander embryos.

Predicting hormesis in mixtures.

Figure 1. Selected concentration–response relationships for the inhibition of root length of Lactuca sativa. The figures, adapted from Belz et al. (2008), illustrate how both the dose range and the size of the maximal response is approximately proportional to the mixture ratio of 50:50%, both for mixtures between 2 hormetic compounds (a) and between a hormetic and a nonhormetic compound (b). L e a rn e d D ico u se PREDICTING HORMESIS IN MIXTURES

Different aspects of hormesis and radiation hormesis

Hormesis is adopted by seeds, plants, micro-organisms, mice, guineapigs and human beings. It is induced by chemicals, pharmaceuticals, heavy metals and toxicological compounds of varied types. Physical inducing agents are temperature and different types of ionizing radiations. Hormesis follows biphasic time-response and dose-response relationships which can be quantitated. The hormetic response is controlled by summation of informations, effectors and sensors. It has been reported in erythropoetic tissue, lymphokine cascade in antibody formation and thymidine reuse in mammals etc. Radiation hormesis is connected with radiation dose, LET, dose rate, size and mass of cells, types of radiation, probability of interaction of radiation with target, time lag between dose and response etc. At its preliminary stage the concept of hormesis was dismissed but later a large number of authors have supported this concept. Mechanistically radiation hormesis can be attributed to different causes namely: (i) cellular damage of DNA and its repair, (ii) mutagenesis and its repair, (iii) micronuclei formation and its repair, (iv) different types of chromosomal aberrations and their repair etc. These repairs are done by antioxidants, different types of enzymes and immune responses and cell cycle control etc. Low dose hormesis has been reported under various conditions namely: (i) environmental and epistemological problems, (ii) background radiation dose estimation, (iii) dose estimation in nuclear installations, (iv) estimation of dose for atomic survivors, (v) accidental dose estimation in Chernobyl etc. In the above cases hormesis depends on internal factors like - lighting condition, intensity and duration of radiation, measurement time of exposure etc. Societal aspects of hormesis e.g. application in biogerontology, radiation protection aspect, increase in life span for cancer - induced patients applying hormetic principles, environmental and toxicological aspects have been mentioned. Future prospects of hormesis (both theoretical and practical) are given below: Theoretical: (i) Low level effects, (ii) linear extrapolation from high level exposure, (iii) shape of dose-response curve and mechanism of radiation effects at low dose, (iv) molecular and cellular studies on mechanism of hormesis. (v) pharmacological hormesis mechanism, (vi) role of hormesis in environmental risk and hazard assessment methods and their evaluation, (vii) role of hormesis in the improvement of harmonization of cancer and non-cancer cases. Practical: (i) Predictive assay of clinical and therapeutic measures using hormetic principles, (ii) toxicological, agricultural, behavioral, societal, biogerontological and economic aspects of hormesis.

Toxic Effect of Inorganic Arsenite [As(III)] on Metabolic Activity of Bacillus subtilis by Combined Methods

In this study, microcalorimetry and measurement of culture turbidity were applied to evaluate the As(III) toxic effect on the metabolic growth of Bacillus subtilis. Using a multichannel thermal activity monitor, the power-time curves of the metabolic activity of B. subtilis during growth in the absence and presence of various concentrations of As(III) were obtained and studied. The turbidity changes during B. subtilis growth with As(III) were investigated by ultraviolet-visible spectrophotometry and the data agree with the results obtained by microcalorimetry. As(III) of various concentrations has different effects on the metabolic growth of B. subtilis with biphasic dose-response relationships called hormesis [i.e., low-concentration stimulation (10 microg/mL) and high-concentration inhibition (20-160 microg/mL). Typical J-shapes of the relationship between the growth rate constant (k) and c, and toxicity at the half-inhibitory concentration (IC(50)) of 98.82 +/- 7.32 microg/mL were obtained. The similarity between the two methods corroborates the validity and sensitivity of the microcalorimetric technique to investigate the toxic effect of As(III) on microorganisms.

Astrocytes: Adaptive Responses to Low Doses of Neurotoxins

This article assesses how astrocytes respond to numerous endogenous agonists and a wide variety of chemical stressors, including well-known neurotoxic agents such as lead and methylmercury, and drugs, within the context of dose-response relationships. In general, astrocytes displayed biphasic dose-response relationships from exposure to neurotoxic agents with temporal and quantitative features similar to hormetic dose responses. While the low-dose stimulatory responses have been viewed as a manifestation of a toxic response, this perspective is being broadly reconsidered and in some cases reinterpreted as being an indicator of an adaptive/protective response. These dose-response patterns are likely to have significant implications in a wide range of conditions affecting normal developmental processes, tumor development, adaptive responses to numerous environmental neurotoxins, and strategies for drug development for the treatment of neurodegenerative conditions.

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

Considerable evidence has emerged that hormetic-like biphasic dose-response relationships are common in the biomedical sciences. Consequently, this article assesses dose-response relationships of agents known to modulate epileptic-like seizure thresholds in screening tests with animal models. Biphasic dose responses have been commonly reported as measured by changes in seizure threshold concentrations across a broad dose-response continuum of chemically diverse agents that act via different receptor-based mechanisms. Despite such differences in chemical structure and modes of actions, the quantitative features of these dose responses are quite similar, being consistent with the hormetic dose-response model with respect to the magnitude and width of the stimulatory responses. The hormetic responses were also independent of the animal model employed as well as type of seizure-related endpoint measured. These findings support the generalizability of the hormetic dose-response concept and may have important implications for the discovery of antiseizure drugs and their clinical evaluation.

Addiction and Dose Response: The Psychomotor Stimulant Theory of Addiction Reveals That Hormetic Dose Responses Are Dominant

In 1987 Wise and Bozarth proposed a psychomotor stimulant theory of addiction whose most consistent feature was enhanced forward (horizontal) locomotion. While controversial, the theory of Wise and Bozarth has had substantial impact on addiction behavior theory over the past two decades, being cited over 1,400 times. The present assessment places the theoretical formulation of within a dose-response framework. This analysis demonstrates that the psychomotor stimulant effects of addictive drugs routinely display biphasic dose-response relationships that are consistent with the quantitative features of the hormetic dose-response model. This is the case, regardless of addictive agent, animal model, and experimental protocol employed. Not only do these findings suggest an important role for the hormetic dose response model in the assessment of addictive behaviors, they also further extend the generalizability of the hormesis dose-response model concept within the biomedical sciences.

Hormetic-Like Biphasic Dose-Response Relationships Are Resumed in Endocrine Profile During Lead Poisoning in Male Reproduction

ISEE-130 Objective: The objective of this study was to predict the mode of inhibitory actions of lead on steroidogenesis acute regulatory (StAR) protein expression and steroidogenic enzymes on steroidogenesis in MA-10 mouse Leydig tumor cells. Material and Methods: We evaluated our data with linear and second-order polynomial models. The equation and correlation coefficient were calculated by linear regression analysis for the logarithm of Pb concentration versus percent (%) of control and by the second-order polynomial analysis for the logarithm of Pb concentration versus progesterone production or StAR protein expression given as integrated optical density. Results: The correlation coefficients R2 by second-order polynomial were 0.96 for human chorionic gonadotropin-stimulated progesterone production, 0.79 for dibutyryl cAMP-stimulated progesterone production, 0.99 for the expression of StAR protein, 0.92 for P450 side-chain cleavage enzyme activity, and 0.96 for 3b-hydroxysteroid dehydrogenase activity. Conclusions: The hormetic-like biphasic dose-response relationships might be resumed in adaptation of the endocrine profile during lead poisoning in male reproduction.

Dose-response relationships in human experimental exposure to solvents.

Previous studies carried out in the field of experimental toxicology have shown evidence of biphasic dose-response relationships for different experimental models, endpoints and chemicals tested. As these studies excluded humans as the experimental model, we have examined the literature of the last three decades in order to verify data concerning human experimental exposure with the aim of highlighting possible biphasic dose-response relationships. The substances used for experimental exposures included hydrocarbons, esters, alcohols, ketones, ethers, glycoethers, halogenated hydrocarbons, and carbon sulphide; the absorption route was inhalation. We did not detect any biphasic dose-response relationship and, in the studies reviewed, our examination revealed major methodological limitations that prevented us making a more detailed examination of experimental data. We concluded that the experimental data available did not allow us to support evidence of biphasic dose-response relationships in human experimental exposure to the above-mentioned chemical substances.

Hormetic Dose-Response Relationships in Immunology: Occurrence, Quantitative Features of the Dose Response, Mechanistic Foundations, and Clinical Implications

This article provides an assessment of the occurrence of immune-system-related hormetic-like biphasic dose-response relationships. Such dose-response relationships are extensive, with over 90 different immune response-related endpoints reported, induced by over 70 endogenous agonists, over 100 drugs, and over 40 environmental contaminants. Such hormetic responses were reported in over 30 animal models, over a dozen mammalian and human cell lines. These findings demonstrate that immune-system-related hormetic-like biphasic dose-response relationships are common and highly generalizable according to model, endpoint, and chemical class. The quantitative features of the dose response are generally consistent with previously published examples of hormetic dose responses for other biological endpoints. These findings were generally recognized and explicitly discussed by the original authors, often with consideration given to possible mechanistic foundations as well as numerous clinical implications. Despite the recognition by individual authors of the hormetic nature of these observed responses, the overall widespread nature of immune-related hormetic responses has been only little appreciated, with a general lack of insight into the highly generalizable nature of this phenomenon as well as the complex regulatory networks affecting biological switching mechanisms that result in the hormetic responses.

Cancer Biology and Hormesis: Commentary

The observation of biphasic dose-response relationships following exposure to pharmacological and toxicological agents has been well documented. In this review Dr. Calabrese, using published data on human tumor cell lines treated with a variety of agents has provided additional support for the demonstration of hormesis in the cancer process. While this review has restricted the examination to human tumor cell lines, this limitation dose not take away from the value of the treatise and helps to point out the need for further analysis of the biphasic does response in other cancer models including in vivo carcinogenesis studies and human cancer epidemiology. This issue is further enhanced when the potential mechanisms for hormetic responses in the cancer cells are discussed, since the same mechanisms participate in the carcinogenesis process. Overall, this review provides an excellent opening examination into the definition of biphasic dose-response effects of toxic and pharmacological agents in cancer cells.

Ethanol and Hormesis

This article provides a detailed assessment of the toxicological and pharmacological literature concerning alcohol-induced biphasic dose-response relationships. The assessment reveals that alcohol-induced hormetic-like dose-response relationships are commonly observed, highly generalizeable according to model and endpoint and quantitative feature of the dose response. These findings have important implications affecting study design, animal model, and endpoint selection as well as clinical applications.