Enhancement of the stress response by minute amounts of cadmium in sensitized Reuber H35 hepatoma cells

Effect of Homeopathic Treatment on Gene Expression in Copenhagen Rat Tumor Tissues

Background: Increasing evidence suggests that the inability to undergo apoptosis is an important factor in the development and progression of prostate cancer. Agents that induce apoptosis may inhibit tumor growth and provide therapeutic benefit. In a recent study, the authors found that certain homeopathic treatments produced anticancer effects in an animal model. In this study, the authors examined the immunomodulating and apoptotic effects of these remedies. Materials and Methods: The authors investigated the effect of a homeopathic treatment regimen containing Conium maculatum, Sabal serrulata, Thuja occidentalis, and a MAT-LyLu Carcinosin nosode on the expression of cytokines and genes that regulate apoptosis. This was assessed in prostate cancer tissues, extracted from animals responsive to these drugs, using ribonuclease protection assay or reverse transcription polymerase chain reaction. Results: There were no significant changes in mRNA levels of the apoptotic genes bax, bcl-2, bcl-x, caspase-1, caspase-2, caspase-3, Fas, FasL, or the cytokines interleukin (IL)–1α, IL-1β, tumor necrosis factor (TNF)–β, IL-3, IL-4, IL-5, IL-6, IL-10, TNF-α, IL-2, and interferon-γ in prostate tumor and lung metastasis after treatment with homeopathic medicines. Conclusions: This study indicates that treatment with the highly diluted homeopathic remedies does not alter the gene expression in primary prostate tumors or in lung metastasis. The therapeutic effect of homeopathic treatments observed in the in vivo experiments cannot be explained by mechanisms based on distinct alterations in gene expression related to apoptosis or cytokines. Future research should explore subtle modulations in the expression of multiple genes in different biological pathways.

Synergistic effects of toxic elements on heat shock proteins

Heat shock proteins show remarkable variations in their expression levels under a variety of toxic conditions. A research span expanded over five decades has revealed their molecular characterization, gene regulation, expression patterns, vast similarity in diverse groups, and broad range of functional capabilities. Their functions include protection and tolerance against cytotoxic conditions through their molecular chaperoning activity, maintaining cytoskeleton stability, and assisting in cell signaling. However, their role as biomarkers for monitoring the environmental risk assessment is controversial due to a number of conflicting, validating, and nonvalidating reports. The current knowledge regarding the interpretation of HSPs expression levels has been discussed in the present review. The candidature of heat shock proteins as biomarkers of toxicity is thus far unreliable due to synergistic effects of toxicants and other environmental factors. The adoption of heat shock proteins as "suit of biomarkers in a set of organisms" requires further investigation.

Homeopathic drug discovery: theory update and methodological aspect

BACKGROUND

Homeopathy treats patient on the basis of totality of symptoms and is based on the principle of 'like cures like'. It uses ultra-low doses of highly diluted natural substances as remedies that originate from plants, minerals or animals.

OBJECTIVE

The objectives of this review are to discuss concepts, controversies and research related to understanding homeopathy in the light of modern science.

METHODS

Attempts have been made to focus on current views of homeopathy and to delineate its most plausible mechanism(s) of action.

RESULTS

Although some areas of concern remain, research carried out so far both in vitro and in vivo validates the effects of highly diluted homeopathic medicines in a wide variety of organisms.

CONCLUSION

The precise mechanism(s) and pathway(s) of action of highly diluted homeopathic drugs are still unknown.

Hormesis: its impact on medicine and health

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.

Hormesis: why it is important to biogerontologists

This paper offers a broad assessment of the hormetic dose response and its relevance to biogerontology. The paper provides detailed background information on the historical foundations of hormesis, its quantitative features, mechanistic foundations, as well as how the hormesis concept could be further applied in the development of new therapeutic advances in the treatment of age-related diseases. The concept of hormesis has direct application to biogerontology not only affecting the quality of the aging process but also experimental attempts to extend longevity.

Postconditioning hormesis and the homeopathic Similia principle: molecular aspects

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.

Postconditioning hormesis put in perspective: an overview of experimental and clinical studies

A beneficial effect of applying mild stress to cells or organisms, that were initially exposed to a high dose of stress, has been referred to as 'postconditioning hormesis'. The initial high dose of stress activates intrinsic self-recovery mechanisms. Modulation of these endogenous adaptation strategies by administration of a subsequent low dose of stress can confer effects that are beneficial to the biological system. Owing to its potentially therapeutic applications, postconditioning hormesis is subject to research in various scientific disciplines. This paper presents an overview of the dynamics of postconditioning hormesis and illustrates this phenomenon with a number of examples in experimental and clinical research.

Homeopathy: Clarifying its relationship to hormesis

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.

The similia principle: results obtained in a cellular model system

This paper describes the results of a research program focused on the beneficial effect of low dose stress conditions that were applied according to the similia principle to cells previously disturbed by more severe stress conditions. In first instance, we discuss criteria for research on the similia principle at the cellular level. Then, the homologous ('isopathic') approach is reviewed, in which the initial (high dose) stress used to disturb cellular physiology and the subsequent (low dose) stress are identical. Beneficial effects of low dose stress are described in terms of increased cellular survival capacity and at the molecular level as an increase in the synthesis of heat shock proteins (hsps). Both phenomena reflect a stimulation of the endogenous cellular self-recovery capacity. Low dose stress conditions applied in a homologous approach stimulate the synthesis of hsps and enhance survival in comparison with stressed cells that were incubated in the absence of low dose stress conditions. Thirdly, the specificity of the low dose stress condition is described where the initial (high dose) stress is different in nature from the subsequently applied (low dose) stress; the heterologous or 'heteropathic' approach. The results support the similia principle at the cellular level and add to understanding of how low dose stress conditions influence the regulatory processes underlying self-recovery. In addition, the phenomenon of 'symptom aggravation' which is also observed at the cellular level, is discussed in the context of self-recovery. Finally, the difference in efficiency between the homologous and the heterologous approach is discussed; a perspective is indicated for further research; and the relationship between studies on the similia principle and the recently introduced concept of 'postconditioning hormesis' is emphasized.

Laboratory research in homeopathy: pro

Homeopathy is a holistic method of treatment that uses ultralow doses of highly diluted natural substances originating from plants, minerals, or animals and is based on the principle of "like cures like." Despite being occasionally challenged for its scientific validity and mechanism of action, homeopathy continues to enjoy the confidence of millions of patients around the world who opt for this mode of treatment. Contrary to skeptics' views, research on home-opathy using modern tools mostly tends to support its efficacy and advocates new ideas toward understanding its mechanism of action. As part of a Point-Counterpoint feature, this review and its companion piece in this issue by Moffett et al (Integr Cancer Ther. 2006;5:333-342) are composed of a thesis section, a response section in reaction to the companion thesis, and a rebuttal section to address issues raised in the companion response.

Where does homeopathy fit in pharmacy practice?

Homeopathy has been the cause of much debate in the scientific literature with respect to the plausibility and efficacy of homeopathic preparations and practice. Nonetheless, many consumers, pharmacists, physicians, and other health care providers continue to use or practice homeopathic medicine and advocate its safety and efficacy. As drug experts, pharmacists are expected to be able to counsel their patients on how to safely and effectively use medications, which technically includes homeopathic products. Yet many pharmacists feel that the homeopathic system of medicine is based on unscientific theories that lack supporting evidence. Since consumers continue to use homeopathic products, it is necessary for pharmacists to have a basic knowledge of homeopathy and to be able to counsel patients about its general use, the current state of the evidence and its use in conjunction with other medications.

Effect of Low Doses and High Homeopathic Potencies in Normal and Cancerous Human Lymphocytes: An In Vitro Isopathic Study

OBJECTIVES

Biologic effects of high homeopathic potencies can be studied in cell cultures using cell lines or primary cells. We hypothesized that primary cells would be more apt to respond to high potencies than cell lines, especially cancer cell lines. We set out to investigate the effects of low doses and high homeopathic potencies of cadmium chloride, respectively, in an intoxication model with human primary lymphocytes compared to a human leukemia cell line (Jurkat).

DESIGN

Cells were pretreated with either low concentrations (nM-microM) or high potencies (pool 15-20c) of cadmium for 120 hours, following which they were exposed to a toxic treatment with a range of cadmium concentrations (8-80 microM) during 24 hours. Cell viability was eventually assessed by use of the MTS/PES assay. Controls included a vehicle (NaCl 0.9%) for the low concentrations of cadmium or water 15-20c for cadmium 15-20c. A total of 34 experiments were conducted, 23 with low concentrations and 11 with high potencies of cadmium. Data were analyzed by analysis of variance.

RESULTS

Pretreatment with low concentrations or high potencies of cadmium significantly increased cell viability in primary lymphocytes after toxic challenge, compared to control cells (mean effect +/- standard error = 19% +/- 0.9% for low concentrations respectively 8% +/- 0.6% for high potencies of cadmium; p < 0.001 in both cases). The pretreatment effect of low doses was significant also in cancerous lymphocytes (4% +/- 0.5%; p < 0.001), albeit weaker than in normal lymphocytes. However, high homeopathic potencies had no effect on cancerous lymphocytes (1% +/- 1.9%; p = 0.45).

CONCLUSIONS

High homeopathic potencies exhibit a biologic effect on cell cultures of normal primary lymphocytes. Cancerous lymphocytes (Jurkat), having lost the ability to respond to regulatory signals, seem to be fairly unresponsive to high homeopathic potencies.

Efficacy of the potentized homeopathic drug, Carcinosin 200, fed alone and in combination with another drug, Chelidonium 200, in amelioration of p-dimethylaminoazobenzene-induced hepatocarcinogenesis in mice

OBJECTIVES

This study was conducted to examine whether the potentized homeopathic remedy Carcinosin 200, fed alone and in combination with Chelidonium 200, has differential protective effects against p-dimethylaminoazobenzene (p-DAB)-induced hepatocarcinogenesis in mice.

DESIGN

Liver tumors were induced in mice through chronic feeding of p-DAB (initiator) and phenobarbital (PB, promoter). The mice were divided into two subgroups: (1) one was fed potentized Alcohol 200 and served as controls; and (2) the other was fed Carcinosin 200 alone or in combination with Chelidonium 200 and divided into several sets. The relative efficacy of the two potentized remedies, alone or in combination, in combating hepatocarcinogenesis was assessed through several cytogenetical endpoints such as chromosome aberrations, induction of micronuclei, sperm head anomaly, and mitotic index at several intervals of fixation (days 7, 15, 30, 60, 90, and 120). Several toxicity biomarkers such as acid and alkaline phosphatases, glutamate oxaloacetate transaminase, glutamate pyruvate transaminase, and lipid peroxidation activity were also assayed in three organs of treated and control mice. In addition, recovery by the homeopathic drugs, if any, of tissue damage inflicted because of chronic feeding of p-DAB and PB was also assessed by optical, scanning, and transmission electron microscopies of liver done at days 60 and 120.

RESULTS

Both Carcinosin 200 and Chelidonium 200 when administered alone show considerable ameliorative effect against p-DAB-induced hepatocarcinogenesis in mice; but the conjoint feeding of these two drugs appears to have had a slightly greater protective effect.

CONCLUSIONS

These homeopathic remedies have the potential to be used as complementary and alternative medicine in liver cancer therapy, particularly as supporting palliative measures.

Towards understanding molecular mechanisms of action of homeopathic drugs: an overview

The homeopathic mode of treatment often encourages use of drugs at such ultra-low doses and high dilutions that even the physical existence of a single molecule of the original drug substance becomes theoretically impossible. But homeopathy has sustained for over two hundred years despite periodical challenges thrown by scientists and non-believers regarding its scientificity. There has been a spurt of research activities on homeopathy in recent years, at clinical, physical, chemical, biological and medical levels with acceptable scientific norms and approach. While clinical effects of some homeopathic drugs could be convincingly shown, one of the greatest objections to this science lies in its inability to explain the mechanism of action of the microdoses based on scientific experimentations and proofs. Though many aspects of the mechanism of action still remain unclear, serious efforts have now been made to understand the molecular mechanism(s) of biological responses to the potentized form of homeopathic drugs. In this communication, an overview of some interesting scientific works on homeopathy has been presented with due emphasis on the state of information presently available on several aspects of the molecular mechanism of action of the potentized homeopathic drugs.

Genotoxic effects of cadmium chloride and azadirachtin treated singly and in combination in fish

The genotoxic effects of cadmium chloride (CdCl(2)) and azadirachtin (Aza) were assessed singly and conjointly in a fish, Oreochromis mossambicus, with endpoints such as chromosome aberrations, abnormal red cell nuclei, abnormal sperm morphology, and protein content (both qualitative and quantitative) of selected tissues, namely, muscle, heart, eye, brain, gill, liver, spleen, and kidney. The primary objectives were, first, to examine if CdCl(2), a common pollutant, and Aza, a natural product of the neem plant used extensively as an 'ecofriendly' agent for many purposes, had any genotoxic effect of their own on nontarget aquatic organisms of economic importance; and second, if Aza could have any ameliorating effect on CdCl(2)-induced genotoxicity in O. mossambicus tissues. As compared with distilled water-treated controls, both CdCl(2) and Aza induced genotoxicity in O. mossambicus, the former in greater quantity than that produced by Aza. However, Cd-induced toxicity in O. mossambicus appeared to be ameliorated to some extent by Aza.

Ameliorating effect of beta-carotene on ethylmethane sulphonate-induced genotoxicity in the fish Oreochromis mossambicus

Genotoxic effects have been assessed in the fish Oreochromis mossambicus treated separately and conjointly with 0.2% ethylmethane sulphonate (EMS) and 0.05% beta-carotene (BC) during five different time periods (6, 24, 48, 72 and 96 h) by analysis of endpoints such as chromosome aberrations, abnormal red blood cell nuclei, abnormal sperm morphology and protein contents (both qualitative and quantitative) of selected tissues, viz. muscle, heart, eye, brain, gill, liver, spleen and kidney. In addition, the relative efficacy of three doses of BC 0.02, 0.05 and 0.1%, in ameliorating genotoxic effects of 0.2% EMS was also tested after a treatment period of 48 h. EMS caused chromosomal aberrations, nuclear anomalies in red blood cells, abnormal sperm morphology and an apparent alteration of protein synthesis in various tissues. Some of these genotoxic effects of EMS appeared to be ameliorated by all three doses of BC, of which the 0.02% dose showed a marginally better efficacy.

Ameliorating effect of microdoses of a potentized homeopathic drug, Arsenicum Album, on arsenic-induced toxicity in mice

BACKGROUND

Arsenic in groundwater and its accumulation in plants and animals have assumed a menacing proportion in a large part of West Bengal, India and adjoining areas of Bangladesh. Because of the tremendous magnitude of the problem, there seems to be no way to tackle the problem overnight. Efforts to provide arsenic free water to the millions of people living in these dreaded zones are being made, but are awfully inadequate. In our quest for finding out an easy, safe and affordable means to combat this problem, a homeopathic drug, Arsenicum Album-30, appears to yield promising results in mice. The relative efficacies of two micro doses of this drug, namely, Arsenicum Album-30 and Arsenicum Album-200, in combating arsenic toxicity have been determined in the present study on the basis of some accepted biochemical protocols.

METHODS

Mice were divided into different sets of control (both positive and negative) and treated series (As-intoxicated, As-intoxicated plus drug-fed). Alanine amino transferase (ALT) and aspartate amino transferase (AST) activities and reduced glutathione (GSH) level in liver and blood were analyzed in the different series of mice at six different fixation intervals.

RESULTS

Both Arsenicum Album-30 and Arsenicum Album-200 ameliorated arsenic-induced toxicity to a considerable extent as compared to various controls.

CONCLUSIONS

The results lend further support to our earlier views that microdoses of potentized Arsenicum Album are capable of combating arsenic intoxication in mice, and thus are strong candidates for possible use in human subjects in arsenic contaminated areas under medical supervision.

Modification of phospholipids fatty acid composition in reuber H35 hepatoma cells: Effect on HMG-CoA reductase activity

There is controversy about the effect of saturated and polyunsaturated fats on 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase, the main regulatory enzyme of cholesterogenic pathway. Results from dietary studies are difficult to interpret because diets normally contain a mixture of fatty acids. Therefore, we have used Reuber H35 hepatoma cells whose phospholipids were enriched in different individual fatty acids and have studied their effects on the cellular reductase activity. Lauric, myristic, eicosapentaenoic (EPA), and docosahexaenoic (DHA) acids were supplemented to the culture medium coupled to bovine serum albumin. The four fatty acids were incorporated into phospholipids from cells grown in media containing whole serum or lipoprotein-poor serum (LPPS). Reductase activity of cells cultivated in a medium with LPPS was three to four times higher than those cultivated in medium with whole serum. Saturated fatty acids increased reductase activity of cells grown in medium with whole serum, whereas n-3 polyunsaturated fatty acids (PUFA) decreased it. However, both saturated and polyunsaturated fatty acids increased reductase activity when serum lipoproteins were removed. In conclusion, this is one of the first reports demonstrating that saturated and n-3 PUFA only show differential effects on HMG-CoA reductase activity in the presence of lipoproteins.

Identification of 100 KDa protein in sera of mice-treated with Cu(II) complex with superoxide dismutase-mimetic activity

The protein profile of sera isolated from mice pre-treated with Cu(II) complex of Girard T with superoxide dismutase (SOD)-mimetic activity was analyzed using SDS-PAGE. This complex was intraperitoneally administered (10 mg/Kg body weight) to Swiss albino mice. The resolved polypeptides showed a new sharp band at 100 KDa against which a polyclonal antibody was raised in rabbit. Sera of rabbit anti-100 KDa protein was used as a powerful probe for the detection of 100 KDa protein isolated from sera of treated mice. Western blot assays revealed a strong reactive polypeptide band at 100 KDa in sera of the mice, but no cross reaction was observed with sera of normal mice. The identification of purified polypeptide was confirmed by different characterization experiments.

Non-linear effects of cycloheximide in glutamate-treated cultured rat cerebellar neurons

Multiple cell types and organisms across a wide array of phyla and a variety of toxins demonstrate non-linear dose responses to low-level chemical exposures with high doses inhibiting cellular function and low doses stimulating function. We tested whether such non-linear responses to low and ultra-low dose N-methyl-D-aspartate (NMDA), 1-methyl-4-phenylpyridinium (MPP+) or cycloheximide moderated toxic glutamate exposure in cultured cerebellar granule cells. Neurons were incubated over 72 h with successive NMDA, MPP+ iodide or cycloheximide additions producing specified low (10(-5), 10(-7), 10(-9), 10(-11), and 10(-13) M) and ultra-low (10(-27),10(-29), 10(-63), and 10(-65) M) concentrations. Subsequently these neuronal cells were exposed to a 50% excitotoxic concentration of glutamate for 24 h. Neuronal viability was significantly reduced in neurons treated with micromolar (10(-5) M) cycloheximide whereas viability was enhanced in neurons treated with an ultra-low dose exposure of 10(-27) M cycloheximide. Neither NMDA nor MPP+ elicited harmful or protective responses. This is the first report demonstrating non-linear dose-response effects of cycloheximide in low and ultra-low concentration ranges.

Proposition of a new system of medicine based on tolerance principle

The author proposes an explanatory model to modify Hahnemann's old tool--"similia similibus curantur"--and suggested a new experimental design to be used to detect the root cause of several chronic diseases and to treat them. All the biochemical reactions of an ideal cell are interlinked by enzymes like a network and shortfall of any one of them may create specific combination of symptoms (e.g., phenylketonuria, alkaptonuria, etc.), due to lack of one or more products that enables us to identify the responsible enzyme. Sometimes malsynthesis of an unknown enzyme(s) or receptors are responsible for a chronic disease and it becomes difficult to identify them by merely observing symptoms. Hence involvement of a normal healthy person ("prover") would be essential to detect it. If an inhibitor that comes from a drug is able to bring the same combination of symptoms in prover it may be predicted that the drug is able to bind and inhibit the responsible enzyme or its product. Minute doses of the same inhibitor(s) can cure the disease if it can act as the ligand of the same enzyme(s), by increasing the rate of transcription (by a positive feedback loop), to compensate the loss of product of the same. The ligand-inhibitor should be trapped in by an organic molecule, like ethanol by the process of potentization to increase the invasiveness of the medicine and to avoid detoxification mechanism, baffling of which increases the concentration of inhibitor inside the cell in course. The cells able to cope up with the stress by the operation of positive feedback loop or compensation cycle synthesize more enzymes and multiply rapidly, but those cells unable to tolerate such stress gradually perish. Thus Hahnemann's principle being dependent on the cause of symptoms becomes modified as "similia similibus curantur causosymptomically".

Upregulation of stress response mRNAs in COS-7 cells exposed to cadmium

Exposure of cells to cadmium (Cd) is known to stimulate the expression of various types of genes. These changes in gene expression are presumed to be related to the cellular response to Cd toxicity. To better understand the mechanisms related to Cd toxicity, suppression subtractive hybridization was carried out on COS-7 cells (African green monkey kidney cells) and the gene expression induced by Cd exposure was investigated. Heat shock protein (hsp) 10, 40, 60, 70, 89alpha and metallothionein II (MTII) mRNAs were found to be induced by Cd. This is the first report to describe the Cd-inducibility of hsp10, 40 and 89alpha mRNAs. Semi-quantitative reverse-transcription polymerase chain reaction showed the diverse expression patterns of these genes, depending on Cd concentration and exposure time. A marked elevation of hsp70 mRNA and induction of mRNA for the co-chaperone, hsp40, were detected. A relatively low level of hsp10 and hsp60 mRNAs was induced, with only a 2-fold increase within 24 h. Hsp89alpha mRNA was induced shortly after Cd exposure. These various induction patterns suggest that hsps play different roles in the cell against Cd toxicity.

Neuroprotection from glutamate toxicity with ultra-low dose glutamate

The protective effects of ultra-low doses (ULD) of glutamate against glutamate toxicity was studied in primary rat spinal, cortical and cerebellar neurons. Neurons were exposed to four subtoxic, ultra-low concentrations of glutamate (10(-18) M, 10(-20)M, 10(-22) M and 10(-30) M) for 72 h and then subsequently challenged with toxic concentrations (25 microM) of glutamate. Neuron viability was consistently 10% higher in spinal and cortical neurons pre-exposed to glutamate concentrations of 10(-18) M and 10(-22) M, and in cerebellar neurons pre-exposed to 10(-20) M and 10(-30) M. Using laser scanning confocal microscopy and the fluorescent calcium probe fluo-3, we found no alterations in intracellular calcium dynamics in the protected cells. This protective effect is consistent with a growing body of evidence for tolerance induced by low-dose toxin exposure but is the first time that such tolerance has been demonstrated with ultra-low glutamate exposure. Our data show that pre-exposure of neuronal cells to ULD glutamate can protect against subsequent exposure to toxic levels of glutamate.

Expression of heat shock protein 60 in human proximal tubule cells exposed to heat, sodium arsenite and CdCl(2)

The expression of hsp 60 mRNA and protein were determined in human proximal tubule cells (HPT) exposed to lethal and sub-lethal concentrations of Cd(2+) under both acute and extended conditions of exposure. It was demonstrated that HPT cells exhibited the classic heat shock response when subjected to a physical (heat) or chemical stress (sodium arsenite). Heat stress, elevated temperature at 42.5 degrees C for 1 h, caused an increase in both hsp 60 mRNA and protein following removal of the stress. Similar results were obtained when the cells were subjected to a classic chemical stress of exposure to 100 microM sodium arsenite for 4 h. Acute exposure of HPT cells to 53.4 microM CdCl(2) for 4 h also resulted in an increase in hsp 60 mRNA and protein following removal of the metal. An extended exposure to Cd(2+) was modeled by treating the cells continuously with Cd(2+) at both lethal and sub-lethal levels over a 16-day time course. It was demonstrated that chronic exposure to Cd(2+) failed to increase either hsp 60 mRNA or protein expression in HPT cells, even at concentrations of Cd(2+) that were lethal to the cells during the time course. In fact, hsp 60 protein levels were decreased compared to controls at lethal levels of Cd(2+) exposure. These findings suggest that hsp 60 expression may have two distinct roles when the human proximal tubule cell is exposed to Cd(2+). A protective role through hsp 60 induction when the proximal tubule cell is acutely exposed to Cd(2+) and a deleterious role when hsp 60 protein is down-regulated during extended exposure to Cd(2+).

Stimulation of survival capacity in heat shocked cells by subsequent exposure to minute amounts of chemical stressors; role of similarity in hsp-inducing effects

A brief and moderate heat shock to Reuber H35 hepatoma cells causes a rapid increase in the synthesis of heat shock proteins (hsp) and initiates the development of thermotolerance, which results in an increased ability to survive exposure to otherwise lethal temperatures. We now demonstrate that low doses of various chemical stressors (arsenite, cadmium, mercury, lead, copper, menadione and diethyldithiocarbamate (ddtc)), at concentrations that do not exert any effect in control cultures, are able to enhance the synthesis of hsps and to stimulate the development of thermotolerance when applied to cultures which were pretreated with a mild heat shock. The degree of stimulation appears to be stressor-specific, which is not only observed in the ensuing development of thermotolerance but also in the enhancement of the heat shock-induced synthesis of stress proteins. The different hsps that show an enhanced induction when heat shocked cultures are exposed to the various secondary applied low doses of chemical stressors, were found to resemble the hsp pattern that is characteristic for the secondary stressor and not for the initial heat shock. In other words, the nature of the post-treatment determines the observed pattern of enhanced synthesis of hsps. In order to analyze the origin of the stimulation of survival capacity by low doses of the mentioned stressors, we studied whether the degree of stimulation is determined by the degree of similarity between the overall stress response to heat shock and to the second stress condition when applied singly. The degree in which low doses of chemical stressors stimulate tolerance development and enhance the synthesis of hsps in cells that were previously heat shocked, appears to be related to the degree of similarity in the hsp pattern induced by both stressors. Our results support the notion that low doses of toxic compounds may, under certain conditions, have beneficial effects related to a stimulation of endogenous cytoprotective mechanisms.

Stressor-specific enhancement of hsp induction by low doses of stressors in conditions of self- and cross-sensitization

In this paper, the pattern of induction of heat shock proteins (hsps) was studied in cultured Reuber H35 rat hepatoma cells by sequential application of different stressors. We analyzed whether a specific stress condition is able to induce an enhanced sensitivity to a subsequent application of a low dose of either the same or another stressor (self-sensitization and cross-sensitization, respectively). As a measure of sensitization, the stimulation of hsp induction was employed. Three different stressor conditions (heat shock, sodium arsenite and cadmium chloride) were used in doses which exerted a similar impact on overall protein synthesis. A synergistic effect in induction of the synthesis of various hsps was observed when a high stressor dose was followed by an 8-h incubation in a lower stressor dose in both self- and cross-sensitization experiments. The low-dose conditions used as second treatments did not induce any responses in non-pretreated cells. Studies in cultured cells have demonstrated stressor-specific hsp induction patterns. In this study we analyzed whether the pattern of hsps induced by the low-dose condition is characteristic for the first sensitizing stressor or for the secondary stressor applied in a low dose. The pattern of hsps which was induced above the level of the high-dose effect, due to the incubation with the secondary applied low-dose condition, was found to be characteristic for the secondary stressor and not for the sensitizing primary treatment. These results are of importance for an improved understanding of the regulation of heat shock protein synthesis in conditions of self- and cross-sensitization, as well as for a proper use of hsps as biomarkers of exposure to environmental stress.