Examining the risks and benefits of replacing traditional dose-response with hormesis

Uncertainty in the results from oral repeated dose toxicity tests: Impact on regulatory classifications

The Lowest Observed (Adverse) Effect Level (LO(A)EL) values are point-of-departure (PoD) values that quantify repeat dose toxicity (RDT). Here, the uncertainty in the regulatory classification of these PoDs is investigated. In the application stage, the dose-response was approximated for a large set of series, giving an account of the possible presence of a hormesis zone. The minimal effect dose (MED) or dose was computed, and the ratio MED/LO(A)EL was used to represent the two components of the experimental uncertainty. The uncertainty estimations were calculated for any combination of gender and reported examination item. Subsequently, how this uncertainty affects the possible classifications was analyzed, and the percentage of the chemicals receiving ambiguous classification was determined. It was shown that more than 40% of the investigated chemicals cannot be classified unambiguously in the Globally Harmonized System (GHS) classification scheme and bear a potential for misclassification when a regulatory decision is based on a single LO(A)EL value. A table containing grey zones for different risk levels and a table with GHS classification distributions for various LO(A)EL values were prepared to facilitate the use of the RDT uncertainty in the practice.

Multiple-species hormetic phenomena induced by indole: A case study on the toxicity of indole to bacteria, algae and human cells

Hormesis is a dose-response relationship phenomenon characterized by low-dose stimulation and high-dose inhibition. Although hormetic phenomena have been reported in broadly ranging biological areas, there is still no unified mechanism of hormesis. Investigating multiple-species hormesis of one compound and then exploring the possible mechanism may be an effective approach to clarify the reason for the occurrence of hormetic phenomena in a broad range of organisms. In this study, indole was selected as the test chemical due to the broad biological and hormetic effects of indole compounds. The results show that indole induces multiple-species hormetic phenomena in bacteria (Aliivibrio fischeri (A. fischeri), Escherichia coli and Bacillus subtilis), algae (Microcystis aeruginosa and Selenastrum capricornutum), and human cells (human skin fibroblasts and human cervical cancer cells). Through in-depth investigation of the time-dependent hormetic effects of indole, indole derivatives and indole's structural analogs on the bioluminescence of A. fischeri, indole ring has been identified as the potential key structure that causes indole to act on quorum sensing of A. fischeri to induce hormetic effects on the bioluminescence at lag, logarithmic, and stationary phases. Therefore, the occurrence of multiple-species hormetic phenomena is speculated to be derived from the action of indole on the cell-to-cell communication of organism cells. This paper can not only further confirm the generalizability of hormesis but also provide a reasonable explanation for hormesis, which will benefit the development of hormesis and the risk assessment of environmental pollutants.

Hormetic use of stress in gerontological interventions requires a cautious approach

Hormesis as a general principle is conceivable only for factors that are present in the natural environment. For such factors, existence of an optimal level can be assumed, which would correspond to the current environmental level or some average of historic levels. Theoretic basis of some hormetic mechanisms has been discussed within the scope of stress response pathways. Impacts of multiple stressing agents may produce combined effects larger than those expected from isolated impacts i.e. act synergistically. Adding the effect of a damaging stress to another damaging stress would possibly augment the damage; but if two mild stresses have positive hormetic effects, their combination can have additive positive effects. Potential adverse effects of excessive doses of hormetic agents should be pointed out particularly for senile age or a state close to decompensation when minor stimuli might be damaging. In conclusion, a hormetic use of stress in gerontological interventions requires a cautious approach.

Hormesis and homeopathy: The artificial twins

Homeopathy claims a curative reaction from small doses of a substance, high doses of which cause symptoms similar to those the patient is suffering from. Hormesis is a concept of biphasic dose-response to different pharmacological and toxicological agents. According to this concept, a small dose of a noxious agent can exert a beneficial action. A hypothesis is defended here that hormesis as a general principle can be assumed only for the factors present in the natural environment thus having induced adaptation of living organisms. Generalizations of the hormesis phenomenon used in support of homeopathy are unfounded. Low-dose impacts may be associated with a higher risk in a state of organ sub-compensation or failure especially in the elderly patients. Practical recommendations should be based neither on the hormesis as a default approach nor on the postulates of homeopathy. All clinically relevant effects, hormetic or not, should be tested by the methods of evidence-based medicine.

Modeling non-monotonic dose-response relationships: model evaluation and hormetic quantities exploration

Non-monotonic (biphasic) dose-response relationships, known as hormetic relationships, have been observed across multiple experimental systems. Several models were proposed to describe non-monotonic relationships. However, few studies provided comprehensive description of hermetic quantities and their potential application. In this study, five biphasic models were used to fit five hormetic datasets from three different experimental systems of our lab. The bisection algorithm based on individual monotone functions was proposed to calculate arbitrary hormetic quantities instead of traditional methods (e.g., model reparameterization) which need complex mathematical manipulation. Results showed that all the five biphasic models could describe those datasets fairly well with coefficient of determination ( R(2) adj) greater than 0.95 and root mean square error (RMSE) smaller than 0.10. The best-fit model could be selected based on EC(R10), RMSE, and a supplemental criterion of Akaike information criterion (AIC). Hormetic quantities that trigger 10% stimulation at the left (EC(L10)) and right (EC(R10)) side of stimulatory peak were calculated and emphasized for their implication in hormesis exploration for the first time. Furthermore, the EC(L10), proposed as an alarm threshold for hormesis, was expected to be useful in risk assessment of environmental chemicals. This study lays a foundation in the quantitative description of the low dose hormetic effect and the investigation of hormesis in environmental risk assessment.

Science, hormesis and regulation

While hormesis is an intriguing scientific hypothesis, this paper argues that it is not yet an acceptable basis for policy-making. Two reasons are given for this assessment. First, although hormesis has suggestive explanatory power, it does not yet have the predictive successes that indicate a general reliability sufficient for policy-making. Second, the regulatory agenda for chemical exposures is usually focused, for good ethical reasons, on protecting people from involuntary and potentially harmful exposures, rather than focused on maximizing public health benefits.

Immunology and homeopathy. 2. Cells of the immune system and inflammation

Here we describe the results of some experimental laboratory studies aimed at verifying the efficacy of high dilutions of substances and of homeopathic medicines in models of inflammation and immunity. Studies carried out on basophils, lymphocytes, granulocytes and fibroblasts are reviewed. This approach may help to test under controlled conditions the main principles of homeopathy such as 'similarity' of drug action at the cellular level and the effects of dilution/dynamization on the drug activity. The current situation is that few and rather small groups are working on laboratory models for homeopathy. Regarding the interpretation of data in view of the simile principle, we observe that there are different levels of similarity and that the laboratory data give support to this principle, but have not yet yielded the ultimate answer to the action mechanism of homeopathy. Evidence of the biological activity in vitro of highly diluted-dynamized solutions is slowly accumulating, with some conflicting reports. It is our hope that this review of literature unknown to most people will give an original and useful insight into the 'state-of-the-art' of homeopathy, without final conclusions 'for' or 'against' this modality. This kind of uncertainty may be difficult to accept, but is conceivably the most open-minded position now.

Can hormesis be a default for dose-response?

Since the 1920s, interest in hormesis has peaked and ebbed. Hormesis had been a forgotten theory until recent investigation by Dr Ed Calabrese at the University of Massachusetts, along with others, resurrected it from obscurity. This renewed interest is demonstrated by recent articles in prestigious scientific journals such as Nature and Science as well as the popular press (Discovery, US News and World Report and newspapers such as the Boston Globe). Currently, a strong interest in this theory of dose-response (which predicts contrasting effects at low versus high doses) exists and is explored in this issue.