Assessment of nonlinear dose-response relationships via nonparametric regression

We propose a simple approach to assess whether a nonlinear parametric model is appropriate to depict the dose-response relationships and whether two parametric models can be applied to fit a dataset via nonparametric regression. The proposed approach can compensate for the ANOVA, which is sometimes conservative, and is very easy to implement. We illustrate the performance by analyzing experimental examples and a small simulation study.

Acute heat priming promotes short-term climate resilience of early life stages in a model sea anemone

Across diverse taxa, sublethal exposure to abiotic stressors early in life can lead to benefits such as increased stress tolerance upon repeat exposure. This phenomenon, known as hormetic priming, is largely unexplored in early life stages of marine invertebrates, which are increasingly threatened by anthropogenic climate change. To investigate this phenomenon, larvae of the sea anemone and model marine invertebrate Nematostella vectensis were exposed to control (18 °C) or elevated (24 °C, 30 °C, 35 °C, or 39 °C) temperatures for 1 h at 3 days post-fertilization (DPF), followed by return to control temperatures (18 °C). The animals were then assessed for growth, development, metabolic rates, and heat tolerance at 4, 7, and 11 DPF. Priming at intermediately elevated temperatures (24 °C, 30 °C, or 35 °C) augmented growth and development compared to controls or priming at 39 °C. Indeed, priming at 39 °C hampered developmental progression, with around 40% of larvae still in the planula stage at 11 DPF, in contrast to 0% for all other groups. Total protein content, a proxy for biomass, and respiration rates were not significantly affected by priming, suggesting metabolic resilience. Heat tolerance was quantified with acute heat stress exposures, and was significantly higher for animals primed at intermediate temperatures (24 °C, 30 °C, or 35 °C) compared to controls or those primed at 39 °C at all time points. To investigate a possible molecular mechanism for the observed changes in heat tolerance, the expression of heat shock protein 70 (HSP70) was quantified at 11 DPF. Expression of HSP70 significantly increased with increasing priming temperature, with the presence of a doublet band for larvae primed at 39 °C, suggesting persistent negative effects of priming on protein homeostasis. Interestingly, primed larvae in a second cohort cultured to 6 weeks post-fertilization continued to display hormetic growth responses, whereas benefits for heat tolerance were lost; in contrast, negative effects of short-term exposure to extreme heat stress (39 °C) persisted. These results demonstrate that some dose-dependent effects of priming waned over time while others persisted, resulting in heterogeneity in organismal performance across ontogeny following priming. Overall, these findings suggest that heat priming may augment the climate resilience of marine invertebrate early life stages via the modulation of key developmental and physiological phenotypes, while also affirming the need to limit further anthropogenic ocean warming.

Physiological Performance Curves: When Are They Useful?

This review serves as an introduction to a special issue of Frontiers in Physiology, focused on the importance of physiological performance curves across phylogenetic and functional boundaries. Biologists have used performance curves to describe the effects of changing environmental conditions on animal physiology since the late 1800s (at least). Animal physiologists have studied performance curves extensively over the past decades, and there is a good foundation to understanding how the environment affects physiological functions of individuals. Our goal here was to build upon this research and address outstanding questions regarding the mutability and applicability of performance curves across taxonomic groups and levels of biological organization. Performance curves are not fixed at a taxonomic, population, or individual level – rather they are dynamic and can shift in response to evolutionary pressures (e.g., selection) and epigenetic programming (e.g., plasticity). The mechanisms underlying these shifts are being increasingly used to predict the efficacy with which plasticity and heritability of performance curves can render individuals and populations less vulnerable to climate change. Individual differences in physiological performance curves (and plasticity of performance curves) can also have cascading effects at higher levels of biological organization. For instance, individual physiology likely influences group behaviors in non-additive ways. There is a need therefore to extend the concept of performance curves to social interactions and sociality. Collectively, this special issue emphasizes the power of how within- and between-individual shifts in performance curves might scale up to the population-, species-, and community-level dynamics that inform conservation management strategies.

The gold-standard in preclinical abuse liability testing: It's all relative

All new molecular entities (NMEs) with targeted or indirect effects on the central nervous system (CNS) must be evaluated for their abuse liability as a part of their nonclinical development plan. Inherently key in the drug control review is the term "relative abuse liability". The basis for determination of drug control is critically dependent on the nonclinical assessment of the reinforcing attributes of the NME in animals (rat is the regulatory preferred species) in a standard operant conditioning paradigm. Pharmaceutical representatives without a background in behavioral analysis or operant conditioning models must weigh through conceptually-intriguing language and constructs that accurately convey and communicate the relative potential for abuse to drug regulatory experts in the field. Effective statutory language in the preclinical assessment of relative abuse liabilities for schedule control status reviews must be 1) specific; 2) concise; 3) familiar to the regulators; 4) unambiguous; 5) constructive; and 6) formalized with respect to both international and national drug control policies. In this review we attempt to define and highlight the importance of the statutory language used to report self-administration study results to both parties engaged in NDA approval process.

Chronic Exposure to the Fusarium Mycotoxin Deoxynivalenol: Impact on Performance, Immune Organ, and Intestinal Integrity of Slow-Growing Chickens

This study investigates the long-term effects of deoxynivalenol (DON) consumption on avian growth performance, on the proliferation, apoptosis, and DNA damage of spleen cells, and on intestinal integrity. Two hundred and eight 5-day-old black-feathered Taiwan country chickens were fed diets containing 0, 2, 5, and 10 mg/kg of DON for 16 weeks. Body weight gain of male birds in the 2 mg/kg group was significantly lower than that in the 5 mg/kg group. At the end of trial, feeding DON-contaminated diets of 5 mg/kg resulted in heavier spleens. Moreover, the increase in DON induced cellular proliferation, apoptosis, and DNA damage signals in the spleen, the exception being female birds fed 10 mg/kg of DON showing reduced proliferation. Expression of claudin-5 was increased in jejunum of female birds fed 2 and 5 mg/kg of DON, whereas decreased expression levels were found in male birds. In conclusion, our results verified that DON may cause a disturbance to the immune system and alter the intestinal barrier in Taiwan country chickens, and may also lead to discrepancies in growth performances in a dose- and sex-dependent manner.

Toxicogenetic effects of low concentrations of the pesticides imidacloprid and sulfentrazone individually and in combination in in vitro tests with HepG2 cells and Salmonella typhimurium

The insecticide imidacloprid and the herbicide sulfentrazone are two different classes of pesticides that are used for pest control in sugarcane agriculture. To evaluate the genotoxic potential of low concentrations of these two pesticides alone and in mixture, the comet assay and the micronucleus (MN) test employing fluorescence in situ hybridization (FISH) with a centromeric probe were applied in human hepatoma cell lines (HepG2), in a 24-h assay. Mutagenicity was assessed by Salmonella/microsome assay with TA98 and TA100 strains in the absence and presence of an exogenous metabolizing system (S9). The results showed significant inductions of MN in HepG2 cells by both pesticides, for all the tested concentrations. As evidenced in the comet assay, only the imidacloprid presented significant responses. When the two pesticides were associated, a significant induction of damage was observed in the HepG2 cells by the comet assay, but not by the MN test. Moreover, the MN induced by the mixtures of the pesticides appeared at lower levels than those induced by sulfentrazone and imidacloprid when tested alone. According to the FISH results, the damage induced by imidacloprid in the HepG2 cells resulted from a clastogenic action of this insecticide (76.6% of the MN did not present a centromeric signal). For the herbicide sulfentrazone and for the mixture of the pesticides, a similar frequency of MN with and without the presence of the centromeric signal (herbicide: 52.45% of the MN without centromeric signal and 47.54% of the MN with centromeric signal; mixture: 48.71% of the MN without centromeric signal and 51.42% of the MN with centromeric signal) was verified. Based on these results, it was concluded that each one of the pesticides evaluated interacts with the DNA of HepG2 cells and causes irreparable alterations in the cells. However, the combination of the pesticides showed an antagonistic effect on the cells and the damage induced was milder and not persistent in HepG2 cells. The results obtained by the Ames test did not point out significant results.

An automated fitting procedure and software for dose-response curves with multiphasic features

In cancer pharmacology (and many other areas), most dose-response curves are satisfactorily described by a classical Hill equation (i.e. 4 parameters logistical). Nevertheless, there are instances where the marked presence of more than one point of inflection, or the presence of combined agonist and antagonist effects, prevents straight-forward modelling of the data via a standard Hill equation. Here we propose a modified model and automated fitting procedure to describe dose-response curves with multiphasic features. The resulting general model enables interpreting each phase of the dose-response as an independent dose-dependent process. We developed an algorithm which automatically generates and ranks dose-response models with varying degrees of multiphasic features. The algorithm was implemented in new freely available Dr Fit software (sourceforge.net/projects/drfit/). We show how our approach is successful in describing dose-response curves with multiphasic features. Additionally, we analysed a large cancer cell viability screen involving 11650 dose-response curves. Based on our algorithm, we found that 28% of cases were better described by a multiphasic model than by the Hill model. We thus provide a robust approach to fit dose-response curves with various degrees of complexity, which, together with the provided software implementation, should enable a wide audience to easily process their own data.

Radiation-hormesis phenotypes, the related mechanisms and implications for disease prevention and therapy

Humans are continuously exposed to ionizing radiation throughout life from natural sources that include cosmic, solar, and terrestrial. Much harsher natural radiation and chemical environments existed during our planet's early years. Mammals survived the harsher environments via evolutionarily-conserved gifts ̶ a continuously evolving system of stress-induced natural protective measures (i.e., activated natural protection [ANP]). The current protective system is differentially activated by stochastic (i.e., variable) low-radiation-dose thresholds and when optimally activated in mammals includes antioxidants, DNA damage repair, p53-related apoptosis of severely-damaged cells, reactive-oxygen-species (ROS)/reactive-nitrogen-species (RNS)- and cytokine-regulated auxiliary apoptosis that selectively removes aberrant cells (e.g., precancerous cells), suppression of disease promoting inflammation, and immunity against cancer cells. The intercellular-signaling-based protective system is regulated at least in part via epigenetic reprogramming of adaptive-response genes. When the system is optimally activated, it protects against cancer and some other diseases, thereby leading to hormetic phenotypes (e.g., reduced disease incidence to below the baseline level; reduced pain from inflammation-related problems). Here, some expressed radiation hormesis phenotypes and related mechanisms are discussed along with their implications for disease prevention and therapy.

Hormesis, cellular stress response and vitagenes as critical determinants in aging and longevity

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 co-ordinating 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, such as carnosine, carnitines or polyphenols, 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. In this review we discuss the most current and up to date understanding of the possible signaling mechanisms by which caloric restriction, as well hormetic caloric restriction-mimetics compounds by activating vitagenes can enhance defensive systems involved in bioenergetic and stress resistance homeostasis with consequent impact on longevity processes.

Sublethal Doses of Mefenoxam Enhance Pythium Damping-off of Geranium

The effect of sublethal doses of fungicides on fungicide-resistant Pythium isolates is unknown but potentially relevant to disease management. Occasional grower reports of Pythium disease increases after fungicide applications and our observations of greater radial growth in vitro on fungicide-amended media than on nonamended media suggests that Pythium isolates may be stimulated by sublethal doses of fungicides. The objectives of this study were to determine whether Pythium isolates were stimulated by sublethal doses of mefenoxam in vitro and whether this stimulation had any influence on Pythium damping-off of geranium seedlings. A mefenoxam-resistant isolate of Pythium aphanidermatum displayed 10% mean radial growth increase in vitro with mefenoxam at 1 × 10^-10 μg/ml compared with growth on nonamended agar (nonsignificant). Geranium seedlings treated with one of eight mefenoxam concentrations were inoculated with 5-mm-diameter colonized agar plugs and evaluated for disease severity every 24 h. The area under the disease progress curve and the survival curve were estimated for each treatment and compared. Significant increases in damping-off were observed with mefenoxam at 1 × 10^-6 and 1 × 10^-10 μg/ml. Our data indicate that a Pythium isolate with resistance to mefenoxam can be stimulated by sublethal doses of the fungicide, and that this stimulation can result in significantly higher rates of Pythium damping-off of geranium seedlings.

Derivation by infrared spectroscopy with multivariate analysis of bimodal contaminant-induced dose-response effects in MCF-7 cells

Toxic responses to contaminants following exposure concentrations typically used in laboratory tests may not reflect how biological systems respond to lower environmental levels from which hormetic effect mechanisms have been suggested. We investigated the pattern of dose-response in mammalian cells to various environmental contaminants using a range of concentrations that span those that are environmentally relevant (10(-12)M to 10(-3)M). MCF-7 cell cultures were treated for 24 h with benzo[a]pyrene (B[a]P), lindane (γ-hexachlorocyclohexane), or polybrominated diphenyl ethers (PBDEs) congeners (47, 153, 183, and 209), then fixed in ethanol and interrogated using attenuated total reflection Fourier-transform infrared (ATR-FTIR) spectroscopy. Mode of action was further studied by examining if test agents stimulated cell growth or altered CYP1A1 expression. Bimodal dose response curves were observed when MCF-7 cells were treated with PBDEs or lindane. The first peak distribution was associated with lower doses (10(-12)M to 10(-9)M), while the second occurred only after MCF-7 cells were exposed to concentrations >10(-9)M. Cellular alterations associated with low-dose PBDEs were mainly due to lipid and secondary protein structural changes, whereas lindane induced DNA/RNA effects as well. In contrast, DNA-reactive B[a]P gave rise to a monotonic linear dose-response relationship and induced mainly DNA/RNA cellular changes. This study shows that environmentally realistic exposures to chemical contaminants can induce nonmonotonic dose-responses in cellular systems.

Ideological toxicology: invalid logic, science, ethics about low-dose pollution

As illustrated by the case of ethanol, claim H is that, for some biological endpoints, low-dose toxins and carcinogens exhibit hormesis, a beneficial or adaprive response characterized by biphasic dose responses and resulting from compensatory biological processes following an initial disruption in homeostasis. From this uncontroversial claim H, however, the paper argues that some toxicologists invalidly infer HG (that H is generalizable across biological model, endpoint measured, and chemical class) and HD (that a strong case can be made for the use of hormesis H as a default assumption in the risk-assessment/regulation process), Evaluating HG and HD, this paper argues for 5 claims. While (1) H is true, (2) HG falls victim to several logical fallacies and therefore is logically, scientifically, and ethically invalid. (3) Because it relies on logical fallacies, confuses necessary and sufficient conditions, and violates at least 5 sets of ethical norms, HD is logically, scientifically, and ethically invalid. (4) Five remedies could help address HG-HD flaws and failure to adequately assess low-dose exposures. (5) Three objections to these criticisms of HG and HD are easily answered.

A perspective on the scientific, philosophical, and policy dimensions of hormesis

The hormesis concept has broad implications for biology and the biomedical sciences. This perspective on hormesis concentrates on toxicology and toxicological risk assessment and secondarily explores observations from other fields. It considers the varied manifestations of hormesis in the context of a broad family of biological stress responses. Evidence for hormesis is reviewed, and the hormesis model is contrasted with more widely accepted dose-response models in toxicology: a linear nonthreshold (LNT) model for mutagenesis and carcinogenesis, and a threshold model for most other toxicologic effects. Scientific, philosophical, and political objections to the hormesis concept are explored, and complications in the hormesis concept are analyzed. The review concludes with a perspective on the current state of hormesis and challenges that the hormesis model poses for risk assessment.

Steroid secretion following exposure of ovarian follicular cells to three different natural mixtures of persistent organic pollutants (POPs)

This study investigated in vitro endocrine disrupting effects of three mixtures of POPs: 'Marine mix' extracted from Atlantic cod liver, and two mixtures extracted from burbot liver, 'Mjøsa mix' and 'Losna mix'. The POP mixtures were chemically characterized. Co-culture of theca and granulosa cells, were exposed for 48h with different doses of 'Marine mix', 'Mjøsa mix' or 'Losna mix'. As an end point cell viability was determinated by LDH test, steroid analysis by EIA and caspase-3 by colorimetric substrate. Chemical characterization of the mixtures demonstrated that the 'Marine mix' contained high levels of DDTs and PCBs. In the 'Mjøsa mix', the dominant pollutants were BDEs and HBCD. The concentrations of POPs measured in the 'Losna mix' were considerably lower. All mixtures used in the present study had a stimulatory effect on testosterone and estradiol secretion with 'Marine mix'>'Mjøsa mix'>'Losna mix'. These results show that even a mixture containing background concentrations of POPs significantly affected steroid secretion. A higher steroidogenic response in low dose ranges, compared with high dose ranges indicated xenobiotic-conditioning hormesis. This could complicate predictions of effects in risk assessments.

Hormesis and aging in Caenorhabditis elegans

Hormesis has emerged as an important manipulation for the study of aging. Although hormesis is manifested in manifold combinations of stress and model organism, the mechanisms of hormesis are only partly understood. The increased stress resistance and extended survival caused by hormesis can be manipulated to further our understanding of the roles of intrinsic and induced stress resistance in aging. Genes of the dauer/insulin/insulin-like signaling (IIS) pathway have well-established roles in aging in Caenorhabditis elegans. Here, we discuss the role of some of those genes in the induced stress resistance and induced life extension attributable to hormesis. Mutations in three genes (daf-16, daf-18, and daf-12) block hormetically induced life extension. However, of these three, only daf-18 appears to be required for a full induction of thermotolerance induced by hormesis, illustrating possible separation of the genetic requirements for stress resistance and life extension. Mutations in three other genes of this pathway (daf-3, daf-5, and age-1) do not block induced life extension or induced thermotolerance; daf-5 mutants may be unusually sensitive to hormetic conditions.

Modelling the effect of autotoxicity on density-dependent phytotoxicity

An established method to separate resource competition from chemical interference is cultivation of monospecific, even-aged stands. The stands grow at several densities and they are exposed to homogenously spread toxins. Hence, the dose received by individual plants is inversely related to stand density. This results in distinguishable alterations in dose-response slopes. The method is often recommended in ecological studies of allelopathy. However, many plant species are known to release autotoxic compounds. Often, the probability of autotoxicity increases as sowing density increases. Despite this, the possibility of autotoxicity is ignored when experiments including monospecific stands are designed and when their results are evaluated. In this paper, I model mathematically how autotoxicity changes the outcome of dose-response slopes as different densities of monospecific stands are grown on homogenously phytotoxic substrata. Several ecologically reasonable relations between plant density and autotoxin exposure are considered over a range of parameter values, and similarities between different relations are searched for. The models indicate that autotoxicity affects the outcome of density-dependent dose-response experiments. Autotoxicity seems to abolish the effects of other phytochemicals in certain cases, while it may augment them in other cases. Autotoxicity may alter the outcome of tests using the method of monospecific stands even if the dose of autotoxic compounds per plant is a fraction of the dose of non-autotoxic phytochemicals with similar allelopathic potential. Data from the literature support these conclusions. A faulty null hypothesis may be accepted if the autotoxic potential of a test species is overlooked in density-response experiments. On the contrary, if test species are known to be non-autotoxic, the method of monospecific stands does not need fine-tuning. The results also suggest that the possibility of autotoxicity should be investigated in many density-response bioassays that are made with even-aged plants, and that measure plant growth or germination.

Lack of effect of metyrapone and exogenous cortisol on early porcine conceptus development

A study was conducted to evaluate the influence of maternal cortisol on early conceptus development in pigs (Sus scrofa). The corticosteroid synthesis inhibitor metyrapone was injected daily during days 14-19 of pregnancy, without (n = 6) and with commensurate administration of cortisol (n = 6). Blood samples were taken via an indwelling jugular catheter on days 14 and 18, and conceptuses were harvested during surgery on day 20. Compared with vehicle-injected control dams (n = 7) plasma cortisol and aldosterone concentrations were decreased (P < 0.01) by 52 and 29%, respectively, by metyrapone treatment. Cortisol administration reversed decreases in plasma cortisol by day 18. There were no treatment-associated effects on conceptus survival or size. Nor were there treatment-associated effects on allantoic fluid volume or content. Trophodermal glucocorticoid receptor (GR) mRNA expression decreased by 34% (P < 0.05) in metyrapone-treated pigs, and was not further influenced by concomitant administration of cortisol, thereby suggesting an influence of aldosterone on GR mRNA expression. Also, when all pigs were considered, there were treatment-independent second-order polynomial regressions (P < 0.05) between maternal plasma cortisol concentrations and embryonic weight, allantoic size and allantoic glucose concentrations, and between plasma aldosterone concentrations and trophodermal GR mRNA expression. Such biphasic corticosteroid concentration versus tissue parameter curves are noteworthy, but difficult to interpret validly. They may suggest that an appropriate corticosteroid environment is necessary for optimal porcine embryonic development during this stage of gestation, but cannot overshadow the absence of treatment effects on the porcine embryonic measures evaluated.

Effects of chromium(VI) and vanadium(V) on the lifespan of fish

The effect of chromium(VI) on the lifespan of laboratory-reared guppies (Poecilia reticulata) has been studied both in the absence and in the presence of the antioxidant D-mannitol, and it has been compared with that produced by vanadium(V). The three substances used as additives exhibited either a weak (D-mannitol), a moderate (chromate) or an acute (vanadate) toxicity to fish. Vanadate, with LC50 (7 days) = 3.84 x 10(-5) mol/L, was about ten times more toxic than chromate, with LC50 (7 days) = 3.42 x 10(-4) mol/L as a single additive and 4.27 x 10(-4) mol/L in the presence of d-mannitol. An increasing effect on the maximum lifespan of males was observed when the additives studied were used at low concentrations, either alone or in a binary combination, following the sequence: vanadate (14%) < D-mannitol (41%) < chromate + D-mannitol (57%) < chromate (69%). Of these substances, only chromate increased also the maximum lifespan of females (72%). The maximum lifespan showed a strong, positive correlation with the concentration of chromate for males (P = 0.00008) and a weaker, positive correlation (P = 0.116) for females. These results suggest the existence of a chemical-hormesis phenomenon that might be subjected to sexual-genre variability. Both the toxicity and the chemical-hormetic effect provoked by chromate were substantially decreased when it was used in combination with d-mannitol, and the possible causes for this double inhibition are briefly discussed.

Low-dose radiation and genotoxic chemicals can protect against stochastic biological effects

A protective apoptosis-mediated (PAM) process that is turned on in mammalian cells by low-dose photon (X and gamma) radiation and appears to also be turned on by the genotoxic chemical ethylene oxide is discussed. Because of the PAM process, exposure to low-dose photon radiation (and possibly also some genotoxic chemicals) can lead to a reduction in the risk of stochastic effects such as problematic mutations, neoplastic transformation (an early step in cancer occurrence), and cancer. These findings indicate a need to revise the current low-dose risk assessment paradigm for which risk of cancer is presumed to increase linearly with dose (without a threshold) after exposure to any amount of a genotoxic agent such as ionizing radiation. These findings support a view seldom mentioned in the past, that cancer risk can actually decrease, rather than increase, after exposure to low doses of photon radiation and possibly some other genotoxic agents. The PAM process (a form of natural protection) may contribute substantially to cancer prevention in humans and other mammals. However, new research is needed to improve our understanding of the process. The new research could unlock novel strategies for optimizing cancer prevention and novel protocols for low-dose therapy for cancer. With low-dose cancer therapy, normal tissue could be spared from severe damage while possibly eliminating the cancer.

A copepod life-cycle test and growth model for interpreting the effects of lindane

A full life-cycle test was performed to measure the effects of lindane (3.2-3,200 microg l(-1)) on the survival, development and reproduction of the freshwater copepod Bryocamptus zschokkei. This copepod survived at relatively high concentrations of lindane compared with other freshwater crustaceans with a 10 day LC50 of 241 microg l(-1) (95% CL of 141-440). 'Equiproportional development', which assumes that each moult stage represents a specific proportion of the total development time, and is not affected by processes that influence metabolism such as temperature and food quality, was used to determine the mode of action of lindane on development in B. zschokkei. Development to adult was significantly longer at 100 microg l(-1) lindane compared with the controls, however, development remained equiproportional regardless of lindane exposure. Increased development times, therefore, are not due to a direct effect of lindane on the moulting process but are due probably to reduced food intake or increased metabolism through the stress imposed by toxicant exposure. Although the survival data suggest that B. zschokkei is relatively tolerant of lindane exposure, reproduction was affected at low lindane concentrations. At 32 microg l(-1) lindane, significantly fewer eggs and viable offspring were produced per female compared with the solvent control. At very low lindane concentrations (3.2 and 10 microg l(-1)), there was a significant increase in the numbers of offspring produced per female compared with the controls and this is interpreted as a hormesis effect. In conclusion, a full life-cycle test demonstrated B. zschokkei is relatively sensitive to lindane compared with other freshwater crustaceans. Incorporating a copepod growth model (equiproportional development) into the life-cycle test design, provided information on the dominant mode of action of the toxicant.

Natural fungicides from Ruta graveolens L. leaves, including a new quinolone alkaloid

Bioassay-directed isolation of antifungal compounds from an ethyl acetate extract of Ruta graveolens leaves yielded two furanocoumarins, one quinoline alkaloid, and four quinolone alkaloids, including a novel compound, 1-methyl-2-[6'-(3' ',4' '-methylenedioxyphenyl)hexyl]-4-quinolone. The (1)H and (13)C NMR assignments of the new compound are reported. Antifungal activities of the isolated compounds, together with 7-hydroxycoumarin, 4-hydroxycoumarin, and 7-methoxycoumarin, which are known to occur in Rutaceae species, were evaluated by bioautography and microbioassay. Four of the alkaloids had moderate activity against Colletotrichum species, including a benomyl-resistant C. acutatum. These compounds and the furanocoumarins 5- and 8-methoxypsoralen had moderate activity against Fusarium oxysporum. The novel quinolone alkaloid was highly active against Botrytis cinerea. Phomopsis species were much more sensitive to most of the compounds, with P. viticola being highly sensitive to all of the compounds.

Hormesis responses of free and immobilized light-emitting bacteria

The stimulatory effect of sublethal or low concentrations of toxic chemicals on organismal metabolism, referred to as hormesis, has been found to be common in the widely used Vibrio fischeri luminescence bioassay. In addition to the "normal" type alpha, we have demonstrated type beta and, possibly, type gamma, dose-response curves in free and immobilized V. fischeri bioassays developed. Understanding and utilizing data from hormesis responses are necessary in determining the toxicity of chemicals, singly or in complex mixtures, to natural biota without imposing excessive penalties to dischargers. At the same time, care must be taken not to relax environmental standards. This can only arise by fully investigating and understanding the role of hormesis in toxicity data used for risk assessment.

Effects of feeding blends of grains naturally contaminated with Fusarium mycotoxins on production and metabolism in broilers

Three hundred sixty, 1-d-old male broiler chicks were fed diets containing grains naturally contaminated with Fusarium mycotoxins for 56 d. The four diets included control (0.14 mg/kg deoxynivalenol, 18 mg/ kg fusaric acid, < 0.1 mg/kg zearalenone), low level of contaminated grains (4.7 mg/kg deoxynivalenol, 20.6 mg/kg fusaric acid, 0.2 mg/kg zearalenone), and high level of contaminated grains without (8.2 mg/kg deoxynivalenol, 20.3 mg/kg fusaric acid, 0.56 mg/kg zearalenone) and with (9.7 mg/kg deoxynivalenol, 21.6 mg/kg fusaric acid, 0.8 mg/kg zearalenone) 0.2% esterified-glucomannan polymer derived from Saccharomyces cerevisiae1026 (E-GM). Body weight gain and feed consumption responded in a significant quadratic fashion to the inclusion of contaminated grains during the finisher period. Efficiency of feed utilization, however, was not affected by diets. The feeding of contaminated grains in the finisher period also caused significant linear increases in blood erythrocyte count and serum uric acid concentration and a significant linear decline in the serum lipase activity. Dietary inclusion of contaminated grains resulted in a significant quadratic effect on serum albumin and y-glutamyltransferase activity. Blood hemoglobin and biliary IgA concentrations, however, responded in significant linear and quadratic fashions. Supplementation of E-GM counteracted most of the blood parameter alterations caused by the Fusarium mycotoxin-contaminated grains and reduced breast muscle redness. It was concluded that broiler chickens may be susceptible to Fusarium mycotoxicoses when naturally contaminated grains are fed containing a combination of mycotoxins.

Radiation hormesis: challenging LNT theory via ecological and evolutionary considerations

Ecological and evolutionary considerations suggest that radiation hormesis is made up of two underlying components. The first (a) is background radiation hormesis based upon the background exposure to which all organisms are subjected throughout evolutionary time. The second and much larger component (b) is stress-derived radiation hormesis arising as a protective mechanism derived from metabolic adaptation to environmental stresses throughout evolutionary time especially from climate-based extremes. Since (b) > > (a), hormesis for ionizing radiation becomes an evolutionary expectation at exposures substantially exceeding background. This biological model renders linear no-threshold theory invalid. Accumulating evidence from experimental organisms ranging from protozoa to rodents, and from demographic studies on humans, is consistent with this interpretation. Although hormesis is not universally accepted, the model presented can be subjected to hypothesis-based empirical investigations in a range of organisms. At this stage, however, two consequences follow from this evolutionary model: (1) hormesis does not connote a value judgement usually expressed as a benefit; and (2) there is an emerging and increasingly convincing case for reviewing and relaxing some recommended radiation protection exposure levels in the low range.