Acute and chronic effects of exposure to a 1-mT magnetic field on the cytoskeleton, stress proteins, and proliferation of astroglial cells in culture

Extremely low-frequency electromagnetic field induces acetylation of heat shock proteins and enhances protein folding

The pervasive weak electromagnetic fields (EMF) inundate the industrialized society, but the biological effects of EMF as weak as 10 µT have been scarcely analyzed. Heat shock proteins (HSPs) are molecular chaperones that mediate a sequential stress response. HSP70 and HSP90 provide cells under undesirable situations with either assisting covalent folding of proteins or degrading improperly folded proteins in an ATP-dependent manner. Here we examined the effect of extremely low-frequency (ELF)-EMF on AML12 and HEK293 cells. Although the protein expression levels of HSP70 and HSP90 were reduced after an exposure to ELF-EMF for 3 h, acetylations of HSP70 and HSP90 were increased, which was followed by an enhanced binding affinities of HSP70 and HSP90 for HSP70/HSP90-organizing protein (HOP/STIP1). After 3 h exposure to ELF-EMF, the amount of mitochondria was reduced but the ATP level and the maximal mitochondrial oxygen consumption were increased, which was followed by the reduced protein aggregates and the increased cell viability. Thus, ELF-EMF exposure for 3 h activated acetylation of HSPs to enhance protein folding, which was returned to the basal level at 12 h. The proteostatic effects of ELF-EMF will be able to be applied to treat pathological states in humans.

Determination of the Impact of High-Intensity Pulsed Electromagnetic Fields on the Release of Damage-Associated Molecular Pattern Molecules

High-Intensity Pulsed Electromagnetic Fields (HI-PEMF) treatment is an emerging noninvasive and contactless alternative to conventional electroporation, since the electric field inside the tissue is induced remotely by an externally applied pulsed magnetic field. Recently, HI-PEMF has been successfully used in the transfer of plasmid DNA and siRNA in vivo, with no or minimal infiltration of immune cells. In addition to gene electrotransfer, treatment with HI-PEMF has also shown potential for electrochemotherapy, where activation of the immune response contributes to the treatment outcome. The immune response can be triggered by immunogenic cell death that is characterized by the release of damage-associated molecular patterns (DAMPs) from damaged or/and dying cells. In this study, the release of the best-known DAMP molecules, i.e., adenosine triphosphate (ATP), calreticulin and high mobility group box 1 protein (HMBG1), after HI-PEMF treatment was investigated in vitro on three different cell lines of different tissue origin and compared with conventional electroporation treatment parameters. We have shown that HI-PEMF by itself does not cause the release of HMGB1 or calreticulin, whereas the release of ATP was detected immediately after HI-PEMF treatment. Our results indicate that HI-PEMF treatment causes no to minimal release of DAMP molecules, which results in minimal/limited activation of the immune response.

The effect of magnetic fields on tumor occurrence and progression: Recent advances

Malignancies are the leading human health threat worldwide. Despite rapidly developing treatments, poor prognosis and outcome are still common. Magnetic fields have shown good anti-tumoral effects both in vitro and in vivo, and represent a potential non-invasive treatment; however, the specific underlying molecular mechanisms remain unclear. We here review recent studies on magnetic fields and their effect on tumors at three different levels: organismal, cellular, and molecular. At the organismal level, magnetic fields suppress tumor angiogenesis, microcirculation, and enhance the immune response. At the cellular level, magnetic fields affect tumor cell growth and biological functions by affecting cell morphology, cell membrane structure, cell cycle, and mitochondrial function. At the molecular level, magnetic fields suppress tumors by interfering with DNA synthesis, reactive oxygen species level, second messenger molecule delivery, and orientation of epidermal growth factor receptors. At present, scientific experimental evidence is still lacking; therefore, systematic studies on the biological mechanisms involved are urgently needed for the future application of magnetic fields to tumor treatment.

Static Magnetic Stimulation Induces Changes in the Oxidative Status and Cell Viability Parameters in a Primary Culture Model of Astrocytes

Astrocytes play an important role in the central nervous system function and may contribute to brain plasticity response during static magnetic fields (SMF) brain therapy. However, most studies evaluate SMF stimulation in brain plasticity while few studies evaluate the consequences of SMF at the cellular level. Thus, we here evaluate the effects of SMF at 305 mT (medium-intensity) in a primary culture of healthy/normal cortical astrocytes obtained from neonatal (1 to 2-day-old) Wistar rats. After reaching confluence, cells were daily subjected to SMF stimulation for 5 min, 15 min, 30 min, and 40 min during 7 consecutive days. Oxidative stress parameters, cell cycle, cell viability, and mitochondrial function were analyzed. The antioxidant capacity was reduced in groups stimulated for 5 and 40 min. Although no difference was observed in the enzymatic activity of superoxide dismutase and catalase or the total thiol content, lipid peroxidation was increased in all stimulated groups. The cell cycle was changed after 40 min of SMF stimulation while 15, 30, and 40 min led cells to death by necrosis. Mitochondrial function was reduced after SMF stimulation, although imaging analysis did not reveal substantial changes in the mitochondrial network. Results mainly revealed that SMF compromised healthy astrocytes' oxidative status and viability. This finding reveals how important is to understand the SMF stimulation at the cellular level since this therapeutic approach has been largely used against neurological and psychiatric diseases.

Electrotransfer of siRNA to Silence Enhanced Green Fluorescent Protein in Tumor Mediated by a High Intensity Pulsed Electromagnetic Field

The contactless high intensity pulsed electromagnetic field (HI-PEMF)-induced increase of cell membrane permeability is similar to conventional electroporation, with the important difference of inducing an electric field non-invasively by exposing a treated tissue to a time-varying magnetic field. Due to the limited number of studies in the field of electroporation induced by HI-PEMF, we designed experiments to explore the feasibility of such a contactless delivery technique for the gene electrotransfer of nucleic acids in tissues in vivo. By using HI-PEMF for gene electrotransfer, we silenced enhanced green fluorescent protein (EGFP) with siRNA molecules against EGFP in B16F10-EGFP tumors. Six days after the transfer, the fluorescent tumor area decreased by up to 39% as determined by fluorescence imaging in vivo. In addition, the silencing of EGFP to the same extent was confirmed at the mRNA and protein level. The results obtained in the in vivo mouse model demonstrate the potential use of HI-PEMF-induced cell permeabilization for gene therapy and DNA vaccination. Further studies are thus warranted to improve the equipment, optimize the protocols for gene transfer and the HI-PEMF parameters, and demonstrate the effects of HI-PEMF on a broader range of different normal and tumor tissues.

Cellular Response to ELF-MF and Heat: Evidence for a Common Involvement of Heat Shock Proteins?

It has been shown that magnetic fields in the extremely low frequency range (ELF-MF) can act as a stressor in various in vivo or in vitro systems, at flux density levels below those inducing excitation of nerve and muscle cells, which are setting the limits used by most generally accepted exposure guidelines, such as the ones published by the International Commission on Non-Ionizing Radiation Protection. In response to a variety of physiological and environmental factors, including heat, cells activate an ancient signaling pathway leading to the transient expression of heat shock proteins (HSPs), which exhibit sophisticated protection mechanisms. A number of studies suggest that also ELF-MF exposure can activate the cellular stress response and cause increased HSPs expression, both on the mRNA and the protein levels. In this review, we provide some of the presently available data on cellular responses, especially regarding HSP expression, due to single and combined exposure to ELF-MF and heat, with the aim to compare the induced effects and to detect possible common modes of action. Some evidence suggest that MF and heat can act as costressors inducing a kind of thermotolerance in cell cultures and in organisms. The MF exposure might produce a potentiated or synergistic biological response such as an increase in HSPs expression, in combination with a well-defined stress, and in turn exert beneficial effects during certain circumstances.

The effects of 50 Hz magnetic field exposure on DNA damage and cellular functions in various neurogenic cells

Epidemiological studies have indicated a possible association between extremely low-frequency magnetic field (ELF-MF) exposure and the risk of nervous system diseases. However, laboratory studies have not provided consistent results for clarifying this association, despite many years of studies. In this study, we have systematically investigated the effects of 50 Hz MF exposure on DNA damage and cellular functions in both neurogenic tumor cell lines (U251, A172, SH-SY5Y) and primary cultured neurogenic cells from rats (astrocytes, microglia, cortical neurons). The results showed that exposure to a 50 Hz MF at 2.0 mT for up to 24 h did not influence γH2AX foci formation (an early marker of DNA double-strand breaks) in any of six different neurogenic cells. Exposure to a 50 Hz MF did not affect cell cycle progression, cell proliferation or cell viability in neurogenic tumor U251, A172 or SH-SY5Y cells. Furthermore, the MF exposure for 24 h did not significantly affect the secretion of cytokines (TNF-α, IL-6 or IL-1β) in astrocytes or microglia, or the phagocytic activity of microglia. In addition, MF exposure for 1 h per day did not significantly influence expression levels of microtubule-associated protein tau, microtubule-associated protein 2, postsynaptic density 95 or gephyrin in cortical neurons, indicating an absence of effects of MF exposure on the development of cortical neurons. In conclusion, our data suggest that exposure to a 50 Hz MF at 2.0 mT did not elicit DNA damage effects or abnormal cellular functions in the neurogenic cells studied.

Electrochemotherapy by pulsed electromagnetic field treatment (PEMF) in mouse melanoma B16F10 in vivo

Introduction

Pulsed electromagnetic field (PEMF) induces pulsed electric field, which presumably increases membrane permeabilization of the exposed cells, similar to the conventional electroporation. Thus, contactless PEMF could represent a promising approach for drug delivery.

Materials and methods

Noninvasive electroporation was performed by magnetic field pulse generator connected to an applicator consisting of round coil. Subcutaneous mouse B16F10 melanoma tumors were treated with intravenously injection of cisplatin (CDDP) (4 mg/kg), PEMF (480 bipolar pulses, at frequency of 80 Hz, pulse duration of 340 μs) or with the combination of both therapies (electrochemotherapy − PEMF + CDDP). Antitumor effectiveness of treatments was evaluated by tumor growth delay assay. In addition, the platinum (Pt) uptake in tumors and serum, as well as Pt bound to the DNA in the cells and Pt in the extracellular fraction were measured by inductively coupled plasma mass spectrometry.

Results

The antitumor effectiveness of electrochemotherapy with CDDP mediated by PEMF was comparable to the conventional electrochemotherapy with CDDP, with the induction of 2.3 days and 3.0 days tumor growth delay, respectively. The exposure of tumors to PEMF only, had no effect on tumor growth, as well as the injection of CDDP only. The antitumor effect in combined treatment was related to increased drug uptake into the electroporated tumor cells, demonstrated by increased amount of Pt bound to the DNA. Approximately 2-fold increase in cellular uptake of Pt was measured.

Conclusions

The obtained results in mouse melanoma model in vivo demonstrate the possible use of PEMF induced electroporation for biomedical applications, such as electrochemotherapy. The main advantages of electroporation mediated by PEMF are contactless and painless application, as well as effective electroporation compared to conventional electroporation.

Elevation of heat shock gene expression from static magnetic field exposure in vitro

Previously, we found that extremely low frequency (ELF) electric fields were able to elicit an approximate 3.5-fold increase in heat shock gene expression, a response which may have applicability to cancer therapy. Based on recent studies demonstrating the ability of magnetic fields to influence gene expression, we hypothesized that low level static magnetic fields may be able to affect heat shock gene expression while avoiding some of the clinical difficulties that arise with electric fields. Transfected rat primary cells in monolayer were exposed to magnetic fields of 1 to 440 mT for 16, 24, or 48 h starting at 24 and 48 h post transfection. Heat shock protein (HSP70) expression, as indicated by a promoter linked luciferase reporter, was followed for up to 96 h and showed a dependence on flux density, exposure duration, and start time post transfection. A nonlinear response was observed for increasing flux density with a maximum of a 3.5-fold increase in expression for 48 h of exposure starting 48 h after transfection. These results demonstrate an enhancement of gene expression similar in magnitude to that observed with external electric field exposure, while eliminating many of the clinical complications.

Extremely low-frequency electromagnetic fields affect transcript levels of neuronal differentiation-related genes in embryonic neural stem cells

Previous studies have reported that extremely low-frequency electromagnetic fields (ELF-EMF) can affect the processes of brain development, but the underlying mechanism is largely unknown. The proliferation and differentiation of embryonic neural stem cells (eNSCs) is essential for brain development during the gestation period. To date, there is no report about the effects of ELF-EMF on eNSCs. In this paper, we studied the effects of ELF-EMF on the proliferation and differentiation of eNSCs. Primary cultured eNSCs were treated with 50 Hz ELF-EMF; various magnetic intensities and exposure times were applied. Our data showed that there was no significant change in cell proliferation, which was evaluated by cell viability (CCK-8 assay), DNA synthesis (Edu incorporation), average diameter of neurospheres, cell cycle distribution (flow cytometry) and transcript levels of cell cycle related genes (P53, P21 and GADD45 detected by real-time PCR). When eNSCs were induced to differentiation, real-time PCR results showed a down-regulation of Sox2 and up-regulation of Math1, Math3, Ngn1 and Tuj1 mRNA levels after 50 Hz ELF-EMF exposure (2 mT for 3 days), but the percentages of neurons (Tuj1 positive cells) and astrocytes (GFAP positive cells) were not altered when detected by immunofluorescence assay. Although cell proliferation and the percentages of neurons and astrocytes differentiated from eNSCs were not affected by 50 Hz ELF-EMF, the expression of genes regulating neuronal differentiation was altered. In conclusion, our results support that 50 Hz ELF-EMF induce molecular changes during eNSCs differentiation, which might be compensated by post-transcriptional mechanisms to support cellular homeostasis.

Effect of 300 mT static and 50 Hz 0.1 mT extremely low frequency magnetic fields on Tuber borchii mycelium

The present work aimed to investigate whether exposure to static magnetic field (SMF) and extremely low frequency magnetic field (ELF-MF) can induce biomolecular changes on Tuber borchii hyphal growth. Tuber borchii mycelium was exposed for 1 h for 3 consecutive days to a SMF of 300 mT or an ELF-MF of 0.1 mT 50 Hz. Gene expression and biochemical analyses were performed. In mycelia exposed to ELF-MF, some genes involved in hyphal growth, investigated using quantitative real-time polymerase chain reaction, were upregulated, and the activity of many glycolytic enzymes was increased. On the contrary, no differences were observed in gene expression after exposure to SMF treatment, and only the activities of glucose 6-phosphate dehydrogenase and hexokinase increased. The data herein presented suggest that the electromagnetic field can act as an environmental factor in promoting hyphal growth and can be used for applicative purposes, such as the set up of new in vitro cultivation techniques.

Is there a relation between extremely low frequency magnetic field exposure, inflammation and neurodegenerative diseases? A review of in vivo and in vitro experimental evidence

Possible health consequences of exposure to extremely low frequency magnetic fields (ELF-MF) have received considerable interest during the last decades. One area of concern is neurodegenerative diseases (NDD), where epidemiological evidence suggests a correlation between MF exposure and Alzheimer's disease (AD). This review is focussing on animal and in vitro studies employing ELF-MF exposures to see if there is mechanistic support for any causal connection between NDD and MF-exposure. The hypothesis is that ELF-MF exposure can promote inflammation processes and thus influence the progression of NDD. A firm conclusion regarding this hypothesis is difficult to draw based on available studies, since there is a lack of experimental studies that have addressed the question of ELF-MF exposure and NDD. Furthermore, the heterogeneity of the performed studies regarding, e.g., the exposure duration, the flux density, the biological endpoint and the cell type and the time point of investigation is substantial and makes conclusions difficult to draw. Nevertheless, the investigated evidence from in vivo and in vitro studies suggest that short-term MF-exposure causes mild oxidative stress (modest ROS increases and changes in antioxidant levels) and possibly activates anti-inflammatory processes (decrease in pro-inflammatory and increase in anti-inflammatory cytokines). The few studies that specifically have investigated NDDs or NDD relevant end-points show that effects of exposure are either lacking or indicating positive effects on neuronal viability and differentiation. In both immune and NDD relevant studies, experiments with realistic long-term exposures are lacking. Importantly, consequences of a possible long-lasting mild oxidative stress are thus not investigated. In summary, the existing experimental studies are not adequate in answering if there is a causal relationship between MF-exposure and AD, as suggested in epidemiological studies.

Response of hippocampal neurons and glial cells to alternating magnetic field in gerbils submitted to global cerebral ischemia

The purpose of this study was to determine whether exposure to an extremely low-frequency magnetic field (ELF-MF, 50 Hz) affects the outcome of postischemic damage in the hippocampus of Mongolian gerbils. After 10-min bilateral carotid occlusion, the gerbils were continuously exposed to ELF-MF (average magnetic induction at the center of the cage was 0.5 mT) for 7 days. The impact of ELF-MF was estimated immediately (the 7th day after reperfusion) and 7 days after cessation of exposure (the 14th day after reperfusion) compared with ischemic gerbils without ELF-MF exposure. Applying stereological methods, histological evaluation of changes in the hippocampus was done for determining its volume, volume densities of degenerating neurons and astrocytes, as well as the number of microglial cells per unit area. ELF-MF per se did not induce any morphological changes, while 10-min global cerebral ischemia led to neuronal death, especially in CA1 region of the hippocampus, as expected. Ischemic gerbils exposed to ELF-MF had significantly a lower degree of cell loss in the examined structure and greater responses of astrocytes and microglial cells than postischemic gerbils without exposure on the seventh day after reperfusion (immediate effect of ELF-MF). Similar response was observed on the 14th day after reperfusion (delayed effect of ELF-MF); however, differences in measured parameters were low and insignificant. Applied ELF-MF has possible neuroprotective function in the hippocampus, as the most sensitive brain structure in the model of global cerebral ischemia, through reduction of neuronal death and activation of astrocytes and microglial cells.

Effects of exposure to a time-varying 1.5 T magnetic field on the neurotransmitter-activated increase in intracellular Ca(2+) in relation to actin fiber and mitochondrial functions in bovine adrenal chromaffin cells

BACKGROUND

It has been reported that exposure to electromagnetic fields influences intracellular signal transduction. We studied the effects of exposure to a time-varying 1.5 T magnetic field on membrane properties, membrane cation transport and intracellular Ca(2+) mobilization in relation to signals. We also studied the mechanism of the effect of exposure to the magnetic field on intracellular Ca(2+) release from Ca(2+) stores in adrenal chromaffin cells.

METHODS

We measured the physiological functions of ER, actin protein, and mitochondria with respect to a neurotransmitter-induced increase in Ca(2+) in chromaffin cells exposed to the time-varying 1.5 T magnetic field for 2h.

RESULTS

Exposure to the magnetic field significantly reduced the increase in [Ca(2+)]i. The exposure depolarized the mitochondria membrane and lowered oxygen uptake, but did not reduce the intracellular ATP content. Magnetic field-exposure caused a morphological change in intracellular F-actin. F-actin in exposed cells seemed to be less dense than in control cells, but the decrease was smaller than that in cytochalasin D-treated cells. The increase in G-actin (i.e., the decrease in F-actin) due to exposure was recovered by jasplakinolide, but inhibition of Ca(2+) release by the exposure was unaffected.

CONCLUSIONS AND GENERAL SIGNIFICANCE

These results suggest that the magnetic field-exposure influenced both the ER and mitochondria, but the inhibition of Ca(2+) release from ER was not due to mitochondria inhibition. The effect of eddy currents induced in the culture medium may indirectly influence intracellular actin and suppress the transient increase in [Ca(2+)]i.

The effect of 100 mT SMF on activation of the hsp70 promoter in a heat shock/luciferase reporter system

Human exposure to magnetic fields, increased through use of new technologies like magnetic resonance imaging (MRI), has prompted investigations into possible effects of static magnetic fields (SMFs) on cellular processes. However, controversy still remains between many studies, which likely results from a lack of uniformity across experimental parameters, including the length of magnetic field exposure, the strength of the magnetic field, and the cell type or organism under investigation. The purpose of this research was to monitor effects of SMF exposure using real-time luminescence photometry. The study investigated the potential interaction of a 100 mT SMF on a heat shock protein (hsp70)/luciferase reporter construct in stably transfected NIH3T3 cells. Changes in heat shock promoter activation following 100 mT SMF exposure were analyzed and detected as bioluminescence in real-time. Two heat parameters were considered in combination with sham- and 100 mT-exposed experiments: no heat or 1,800 s heat. As expected, there was a significant increase in bioluminescence in response to 1,800 s of heat alone. However, no significant difference in average hsp70 promoter activation between sham and 100 mT experiments was observed for no heat or 1,800 s heat experiments. Therefore, a 100 mT SMF was shown to have no effect on the activation of the heat shock protein promoter during SMF exposure or when SMF exposure was combined with a heat insult.

Real-time measurement of cytosolic free calcium concentration in HL-60 cells during static magnetic field exposure and activation by ATP

Calcium ions are involved in a number of important signal transduction pathways in cells. Cytosolic calcium concentration ([Ca(2+)](c)) can be affected by the activation of Ca(2+) channels through the action of ligands such as ATP. The response of [Ca(2+)](c) to ligands may be affected by external factors like magnetic fields. The purpose of this study was to determine if exposure to a static magnetic field (SMF) for 800 s altered the [Ca(2+)](c) response to ATP in undifferentiated HL-60 cells. We sham exposed or field exposed fura-2 loaded HL-60 cells to a SMF of 1, 10, and 100 mT. Cells were activated with ATP 300 s into the exposure. The level of [Ca(2+)](c) was followed before, during, and after field or sham exposure with a ratiometric fluorescence spectroscopy system. It was found that high concentrations of ATP resulted in greater [Ca(2+)](c) responses, but faster recovery to near basal levels. The application of 1, 10, or 100 mT SMF did not affect the [Ca(2+)](c) response to ATP. Future work could examine the effect of a longer SMF exposure on the [Ca(2+)](c) response to ATP. Longer exposures might provide sufficient time for morphological changes in the plasma membrane to occur.

Effects of sinusoidal electromagnetic field on structure and function of different kinds of cell lines

This study investigated that whether a 2 mT, 60 Hz, sinusoidal electromagnetic field (EMF) alters the structure and function of cells. This research compared the effects of EMF on four kinds of cell lines: hFOB 1.19 (fetal osteoblast), T/G HA-VSMC (aortic vascular smooth muscle cell), RPMI 7666 (B lymphoblast), and HCN-2 (cortical neuronal cell). Over 14 days, cells were exposed to EMF for 1, 3, or 6 hours per day (hrs/d). The results pointed to a cell type-specific reaction to EMF exposure. In addition, the cellular responses were dependent on duration of EMF exposure. In the present study, cell proliferation was the trait most sensitive to EMF. EMF treatment promoted growth of hFOB 1.19 and HCN-2 compared with control cells at 7 and 14 days of incubation. When the exposure time was 3 hrs/d, EMF enhanced the proliferation of RPMI 7666 but inhibited that of T/G HA- VSMC. On the other hand, the effects of EMF on cell cycle distribution, cell differentiation, and actin distribution were unclear. Furthermore, we hardly found any correlation between EMF exposure and gap junctional intercellular communication in hFOB 1.19. This study revealed that EMF might serve as a potential tool for manipulating cell proliferation.

Gene expression profiling of human endothelial cells exposed to 50-Hz magnetic fields fails to produce regulated candidate genes

To address the question of a possible effect of magnetic fields (MF) at 50 Hz on living systems, gene expression analyses were performed on human primary vascular endothelial cells exposed to MF of various intensities compared to control cells. Exposure protocols included continuous exposure at a single intensity (10 and 700 microT), intermittent exposure at a single intensity (700 microT), and continuous exposure to a variable-intensity field (10-30 microT). The transcriptional response of the cells was investigated using oligonucleotide microarrays containing up to 30 000 unique features. Although in individual experiments genes were identified where the expression appeared to be affected by exposure to MF, none of these genes were regulated in the same manner in subsequent repetition experiments. This is the first report of a transcriptome-wide analysis of the effects of MF exposure on human cells. The lack of a reproducible effect of MF on the expression of any genes in our investigation adds further weight to the evidence that 50-Hz MF are not capable of interacting with biological systems and thus do not represent an endothelial stress factor.

The influence of extremely low frequency magnetic fields on cytoprotection and repair

Ischemia-reperfusion injuries, such as those suffered from various types of cardiovascular disease, are major causes of death and disability. For relatively short periods of ischemia, much of the damage is potentially reversible and in fact, does not occur until the influx of oxygen during the reperfusion stage. Because of this, there is a window of opportunity to protect the ischemic tissue. Here, we review several mechanisms of protection, such as heat shock proteins, opioids, collateral blood flow, and nitric oxide induction, and the evidence indicating that magnetic fields may be used as a means of providing protection via each of these mechanisms. While there are few studies demonstrating direct protection with magnetic field therapies, there are a number of published reports indicating that electromagnetic fields may be able to influence some of the biochemical systems with protective applications.