Human & Experimental Toxicology

This paper presents the case that certain types of homeopathic medicine may represent a form of hormesis, that is, either pre- or post-conditioning hormesis. An example of a post-conditioning model by van Wijk and colleagues demonstrated successful enhancement of adaptive responses using below-toxic threshold doses (i.e. hormetic doses) of inducing agents when administered subsequent to a highly toxic chemical exposure, thus satisfying a basic experimental biomedical standard. Of note is that this model uses exposures within a measurable predicted hormetic range, unlike most forms of homeopathy. This experimental framework (along with a pre-conditioning model developed by Bellavite) provides a possible vehicle by which certain aspect(s) of homeopathy may be integrated into mainstream biomedical assessment and clinical practice.

Is hormesis related to homeopathy? Despite the superficial similarity of the low dose of the applied stimulus, there are compelling reasons for maintaining hormesis and homeopathy as unrelated. Homeopathy originated in the medical knowledge vacuum of the 19th century, prior to the acceptance of the germ/gene bases of disease. Homeopathy was never grounded on empirical scientific evidence. Hormesis, on the other hand, has always been an empirical science, involving properly controlled experiments. Hormesis is a concept in toxicology that involves biphasic dose responses in biological systems, wherein low doses of stressors can have beneficial effects and higher doses have harmful effects. Hormesis, as it applies to toxicology, is a necessary and useful concept describing adaptive organismic responses to applied stressors. Conversely, homeopathy is a medical doctrine based on the erroneous belief that substances which cause the symptoms of a disorder will cure the disorder when given to patients in small doses. To suggest that homeopathy is a form of post-exposure conditioning hormesis assumes that homeopathic practitioners employed the scientific method with measurable experimental end-points and proper controls, and that their ‘provings’ had actually determined the correct compound, at the correct dose, required to cure a disorder. Because many homeopathic preparations are diluted to a point where none of the starting solutes would likely remain, the idea of a beneficial or harmful hormetic dose becomes moot. Without supporting scientific evidence for the efficacy or purported mechanisms of homeopathy, the term hormesis should not be linked with it in any way.

The concept of hormesis can provide an evaluation framework for the assessment of homeopathic treatment preparations following a post-conditioning hormesis protocol based on the research of van Wijk and colleagues. This proposal would require that doses of administered drug conform to analytical chemistry requirements for quantification. This developmental framework can provide a scientific ‘point of contact’ between the homeopathic and biomedical communities, which has long been lacking.

The scientific foundations of hormesis are now well established and include various biochemical and molecular criteria for testing the hormetic nature of chemicals and other modulators. In order to claim homeopathy as being hormetic, it is essential that, in addition to the hormetic biphasic dose response, homeopathic remedies should fulfill one or more molecular criteria. Since stress response pathways, such as heat shock response, antioxidative response, autophagic response and unfolded protein response, are integral components of the physiological hormesis, it is important that homeopathic drugs be tested for these pathways if these are to be considered as hormetins and to cause hormesis.

Homeopathy is the best known medical analogue of hormesis, others include hormoligosis and paradoxical pharmacology. Homeopathy is based on the concept Similia similibus curentur (‘Let like be cured by like’); the exploitation of secondary effects of drugs, the body’s reaction rather than the primary pharmacological action. The most controversial aspect of homeopathy is its use of ‘ultramolecular’ dilutions in which a single molecule of the starting substance is unlikely to be present. Classical pharmacological actions in vivo have been reported with dilutions as high as 10^-22mol/L, but homeopathic medicines may be far more dilute than this. There is growing biological evidence including independent reproduction that in vivo effects may occur at such dilutions. In a systematic review, 73% of experiments showed an effect with ultramolecular dilutions including 68% of high-quality experiments. Physical and physico-chemical work suggests that homeopathic preparations contain stable ordered supramolecular structures, gas nanobubbles and dissolved silicates may be involved. Homeopathy may contribute to the generalizability and reproducibility of hormesis effects. It also raises the question of the threshold of hormesis effects.

Postexposure conditioning, as a part of hormesis, involves the application of a low dose of stress following exposure to a severe stress condition. Depending on whether the low-dose stress is of the same type of stress or is different from the initial high-dose stress causing the diseased state, postconditioning can be classified as homologous or heterologous, respectively. In clinical homeopathy, the same distinction is found between isopathic and homeopathic application of low-dose substances. Homeopathy is unique for its Similia principle, which implies that substances causing symptoms in healthy biological systems can be used to treat similar symptoms in diseased biological systems. The evaluation of the Similia principle in an experimental set-up requires the analysis of a complex sequence of ‘damage-disease-treatment-effect’ events. The process of recovery from an insult is then monitored and a possible beneficial effect on this recovery process, upon application of a range of substances in low dose, can subsequently be analyzed using molecular and functional parameters. It is then possible to compare the effect of treatment with the degree of similarity between the diseased state and the effects caused by homologous and/or different heterologous substances. Beneficial effects of postconditioning mild stress conditions have been described in terms of an increase of the synthesis of stress proteins. In this commentary paper, we present additional information on this aspect. The experimental data suggest that the beneficial effect of the low-dose stress condition used as heterologous postconditioning is related to similarity in molecular stress response.

Homeopathy is an empirical method of treatment. Hormesis, while stemming from within the rationalist tradition, has yet to be explained according to current pharmacological theory. Both share in common sub-threshold doses of toxic substances and an initial semi-toxicological insult followed by a greater compensatory (or healing) response. We question whether the differences between these fields may be amenable to scientific research. We identify five cardinal differences between homeopathy and hormesis: (1) Hormesis is a universal phenomenon, while homeopathy is highly specific; (2) Hormesis uses only measurable quantities of compounds, as opposed to homeopathy, which frequently administers medicines at dilutions far beyond the material range; (3) Preparation of hormetic solutions follows standard laboratory procedure, while homeopathy requires a sequential series of dilutions, each followed by vigorous shaking (‘succussion’); (4) The effects of hormesis are moderate and temporary, while homeopathy claims curative and permanent responses and (5) Hormesis is a lab phenomenon observed primarily in healthy organisms, whereas homeopathy is a mode of treatment administered primarily to ailing individuals. We believe that all five of these differences are amenable to scientific investigation, and suggest comparing succussed to non-succussed diluted solutions as an optimal first evaluation. We conclude that while certain differences exist between hormesis and homeopathy, hormesis may in fact be a subset of homeopathy.

Homeopathy is an ancient and complex therapeutic method that is rediscovering its scientific foundations. Hormesis is a frequently observed phenomenon that has been rigorously reported with precise dose-response curves. The therapeutic method based on the principle of ‘like cures like’ should not be confused with hormesis, which has several different implications from those of homeopathy. Yet, because both these approaches to nature and medicine are very broad in scope, they do end up having some points of contact. Thus, the well-established and consolidated field of hormesis can help cast light, through its ideas and research methods, on the possible mechanisms of action of remedies in ultra-low doses.

Oxidative stress plays a key role in lead (Pb)-induced nephrotoxicity. N-acetylcysteine (NAC) is a potent oxygen free radicals scavenger and a metal chelator. In the present study, female Sprague-Dawley rats received PbAc₂ (300 mg/L, via drinking water) and/or NAC (100 mg/kg/day, by intraperitoneal injection) to investigate the protective effect of NAC on Pb-induced renal damage and oxidative stress as well as its mechanism of action. Renal toxicity was evaluated by measuring urinary excretion of total protein, β₂-microglobulin, albumin and urinary enzyme markers of tubular necrosis, as well as serum urea nitrogen level. Activities of antioxidant enzymes, contents of glutathione and malondialdehyde in kidney were also measured. Renal cell damage was assessed by electron microscopy. Animals that received both Pb and NAC showed a better renal function than those receiving Pb alone. Lead-induced tubular lesions and mitochondrial damage were markedly reduced in rats that also received NAC. Also, NAC significantly reduced the levels of lipid peroxidation and markedly restored the enzymic and non-enzymatic antioxidants levels in kidney of Pb-treated rats. Moreover, NAC administration significantly increased urinary Pb excretion and decreased its level in the serum and kidney. In conclusion, NAC treatment prevents renal tubular damage induced by chronic Pb administration, most probably through its antioxidant properties and chelating ability.

The aim of this study was to investigate, through the single-cell gel (comet) assay, whether vitamin C is able to protect against renovascular hypertension-induced genotoxicity in multiple organs. A total of 32 male Wistar rats were divided into four groups: negative control (n = 6); animals treated with vitamin C (n = 6); hypertensive rats (n = 10) and hypertensive rats and treated with vitamin C (n = 10). Hypertension was induced as a result of partial obstruction of the left renal artery by means of a silver clip during 6 weeks. Vitamin C was administered at 150 mg/kg during 7 consecutive days before the end of the experimental period. The results showed that vitamin C was able to protect blood cells against hypertension-induced genotoxicity. Brain, liver and heart cells were also protected by vitamin C following hypertension-induced genotoxic damage. Regarding blood pressure, vitamin C reduced the hypertensive state. In conclusion, our results suggest that vitamin C can prevent hypertension-induced DNA damage in blood, liver, brain and heart cells as well as to normalize the blood pressure of rats.

Our studies were performed to investigate the effects of the aqueous extracts of Cecropia pachystachya and Larrea divaricata. These plants are used in folkloric medicine in infusion and were administered orally (0.76 g/kg) to male Albino Swiss mice for 16 days, on drink intake, organ weight/body weight (OW/BW × 100) ratio, histology, broqueoalveolar fluid (BALF) and elevated plus-maze (EPM). Feeding as well as body weight were unaffected by the consumption of these extracts. There were no signs of toxicity in BALF, morbidity or mortality during the study. C. pachystachya caused an increase in relative kidney OW/BW (p ≤ .05 vs control). The macroscopic and microscopic morphologic analyses of the organs were not altered by administration of these plants. A non-anxiolytic-like activity of an aqueous extract prepared from the leaves of C. pachystachya and L. divaricata in EPM was observed. We conclude that the crude aqueous extracts of leaves tested on mice orally did not produce signs of toxicity or behavioral changes in routine histological and clinical evaluation. However, knowledge of the biological activity of many herbal medicine used in Latin American is still deficient and more studies will be needed to elucidate the possible toxic effects.

Carbobenzoxy-Leu-Leu-leucinal (MG132) as a proteasome inhibitor has been shown to induce apoptotic cell death through formation of reactive oxygen species (ROS). In the present study, we evaluated the effects of MG132 on the growth of A549 lung cancer cells in relation to cell growth, ROS and glutathione (GSH) levels. Treatment with MG132 inhibited the growth of A549 cells with an IC₅₀ of approximately 20 μM at 24 hours. DNA flow cytometric analysis indicated that 0.5 ∼ 30 μM MG132 induced a G1 phase arrest of the cell cycle in A549 cells. Treatment with 10 or 30 μM MG132 also induced apoptosis, as evidenced by sub-G1 cells and annexin V staining cells. This was accompanied by the loss of mitochondrial membrane potential (MMP; Δψm). The intracellular ROS levels including O₂ ^•- were strongly increased in 10 or 30 μM MG132-treated A549 cells but were down-regulated in 0.1, 0.5 or 1 μM MG132-treated cells. Furthermore, 10 or 30 μM MG132 increased mitochondrial O₂ ^•- level but 0.1, 0.5 or 1 μM MG132 decreased that. In addition, 10 or 30 μM MG132 induced GSH depletion in A549 cells. In conclusion, MG132 inhibited the growth of human A549 cells via inducing the cell cycle arrest as well as triggering apoptosis, which was in part correlated with the changes of ROS and GSH levels. Our present data provide important information on the anti-growth mechanisms of MG132 in A549 lung cancer cells in relation to ROS and GSH.

Chloroform is a potent central nervous system and respiratory depressant. The toxicities associated with chloroform frequently occur after inhalation. Hepatotoxicity is secondary to production of a toxic metabolite, with a peak elevation of liver enzymes 72 hours after exposure. Acute liver failure after chloroform inhalation is rarely described, this syndrome being produced mainly by viral hepatitis, idiosyncratic drug-induced liver injury, and acetaminophen ingestion. This report describes the case of a 46-year-old woman who presented to emergency department with coma, signs of respiratory failure, and solvent odor of her breath after chloroform inhalation and binge drinking. In evolution appeared lethal acute liver failure and rhabdomyolysis, despite maximum supportive care. Necroptic examination revealed microvesicular steatosis and tubular renal necrosis, specific for chloroform toxicity. This case illustrates the dramatic impact on liver of two well-recognized hepatotoxins. Mechanisms of chloroform and alcohol-induced liver toxicity are reviewed.