A direct correlation between hyperthermia-induced membrane blebbing and survival in synchronous G1 CHO cells

Curcumin and 5-fluorouracil-loaded, folate- and transferrin-decorated polymeric magnetic nanoformulation: a synergistic cancer therapeutic approach, accelerated by magnetic hyperthermia

The efficient targeting and therapeutic efficacy of a combination of drugs (curcumin and 5-Fluorouracil [5FU]) and magnetic nanoparticles encapsulated poly(D,L-lactic-co-glycolic acid) nanoparticles, functionalized with two cancer-specific ligands are discussed in our work. This multifunctional, highly specific nanoconjugate resulted in the superior uptake of nanoparticles by cancer cells. Upon magnetic hyperthermia, we could harness the advantages of incorporating magnetic nanoparticles that synergistically acted with the drugs to destroy cancer cells within a very short period of time. The remarkable multimodal efficacy attained by this therapeutic nanoformulation offers the potential for targeting, imaging, and treatment of cancer within a short period of time (120 minutes) by initiating early and late apoptosis.

Exclusive photothermal heat generation by a gadolinium bis(naphthalocyanine) complex and inclusion into modified high-density lipoprotein nanocarriers for therapeutic applications

A hydrophobic gadolinium bis(naphthalocyanine) sandwich complex (GdSand) possessing several absorbances across visible and infrared wavelengths (up to 2500 nm) was solubilized in aqueous solution by uptake into a nascent mutant high-density lipoprotein (HDL) nanocarrier. The HDL nanocarrier was additionally functionalized with a trans-activator of transcription peptide sequence to promote efficient cell penetration of the drug delivery system (cpHDL). The dye-loaded nanocarrier (GdSand@cpHDL) exhibited photothermal heat generation properties upon irradiation with near-infrared (NIR) laser light, with controllable heat generation abilities as a function of the incident laser light power. Comparison of the photothermal behavior of the dyes GdSand and the well-explored molecular photothermal agent indocyanine green (ICG) in the cpHDL nanocarrier (i.e., ICG@cpHDL) revealed two significant advantages of GdSand@cpHDL: (1) the ability to maintain elevated temperatures upon light absorption for extended periods of time, with a reduced degree of self-destruction of the dye, and (2) exclusive photothermal heat generation with no detectable singlet oxygen production leading to improved integrity of the cpHDL nanocarrier after irradiation. Finally, GdSand@cpHDL was successfully subjected to an in vitro study against NCI-H460 human lung cancer cells, demonstrating the proof-of-principle utility of lanthanide sandwich complexes in photothermal therapeutic applications.

Real-time temperature estimation and monitoring of HIFU ablation through a combined modeling and passive acoustic mapping approach

Passive acoustic mapping (PAM) has been recently demonstrated as a method of monitoring focused ultrasound therapy by reconstructing the emissions created by inertially cavitating bubbles (Jensen et al 2012 Radiology 262 252-61). The published method sums energy emitted by cavitation from the focal region within the tissue and uses a threshold to determine when sufficient energy has been delivered for ablation. The present work builds on this approach to provide a high-intensity focused ultrasound (HIFU) treatment monitoring software that displays both real-time temperature maps and a prediction of the ablated tissue region. This is achieved by determining heat deposition from two sources: (i) acoustic absorption of the primary HIFU beam which is calculated via a nonlinear model, and (ii) absorption of energy from bubble acoustic emissions which is estimated from measurements. The two sources of heat are used as inputs to the bioheat equation that gives an estimate of the temperature of the tissue as well as estimates of tissue ablation. The method has been applied to ex vivo ox liver samples and the estimated temperature is compared to the measured temperature and shows good agreement, capturing the effect of cavitation-enhanced heating on temperature evolution. In conclusion, it is demonstrated that by using PAM and predictions of heating it is possible to produce an evolving estimate of cell death during exposure in order to guide treatment for monitoring ablative HIFU therapy.

Geranylgeranylacetone protects rat and striatum neurons against heat injury via induction of Hsp70

GGA (geranylgeranylacetone) may induce Hsp70 synthesis, thus contributing to the protective effects of GGA in several disease states. This study evaluated the protective effects of GGA against heat injury to rat and striatum neurons in terms of mechanisms. Rats were exposed to 41.5°C for 35 min to induce heatstroke; the protective effects of GGA were then evaluated by change in rectal temperature (Tre) during heat exposure and survival time after heatstroke. Primary cultured striatum neurons were incubated with GGA for 24h, and then heat-treated at 43°C for a further 1h. The viability, membrane surface ultrastructure and Hsp70 expression of striatum neurons were all observed. Furthermore, the effects of quercetin an inhibitor of Hsp70 synthesis were also investigated. Compared to the heatstroke group, GGA delayed Tre in reaching 42.1°C (P<0.05) and prolonged the survival time after heatstroke (P<0.01). The LDH releasing percentage decreased in GGA groups (P<0.05, P<0.01) compared to the heat-treatment group and increased in quercetin groups (P<0.05) compared to GGA group. Results from AFM showed that GGA protected membrane surface ultrastructure against heat injury. In addition, results from Western blot showed that GGA-induced Hsp70 expression of neurons both in normal and heat-treatment conditions (P<0.01, P<0.05) and quercetin inhibited GGA-induced Hsp70 expression (P<0.05). Therefore, GGA had protective effects against heat injury in striatum neurons and rat heatstroke. Quercetin inhibited GGA-induced Hsp70 expression and prevented GGA-protective effects, which indicated that this protection was dependent on the Hsp70 synthesis.

Treatment of burn injury by cellular repair

Burn injury leads to a direct damaging effect on cells, disrupting the assembly of the cell and denaturing proteins. Although modern medicine has significantly improved the survival of burn victims, a method to treat injury at the cellular level is presented. In particular, the cell membrane is most vulnerable to heat injury. Copolymer surfactants have been shown to repair the cell membrane, and agents such as poloxamer 188 have demonstrated this effect in numerous studies. Furthermore, copolymer surfactants have been shown to act as molecular chaperones, allowing denatured proteins to regain their native confirmation. Pharmaceutical agents may be developed to repair the cell membrane and refold proteins, mimicking endogenous repair mechanisms and salvaging cells that would otherwise be lost.

Gold nanorod assisted near-infrared plasmonic photothermal therapy (PPTT) of squamous cell carcinoma in mice

Plasmonic photothermal therapy (PPTT) is a minimally-invasive oncological treatment strategy in which photon energy is selectively administered and converted into heat sufficient to induce cellular hyperthermia. The present work demonstrates the feasibility of in vivo PPTT treatment of deep-tissue malignancies using easily-prepared plasmonic gold nanorods and a small, portable, inexpensive near-infrared (NIR) laser. Dramatic size decreases in squamous cell carcinoma xenografts were observed for direct (P<0.0001) and intravenous (P<0.0008) administration of pegylated gold nanorods in nu/nu mice. Inhibition of average tumor growth for both delivery methods was observed over a 13-day period, with resorption of >57% of the directly-injected tumors and 25% of the intravenously-treated tumors.

MRI-guided Thermal Ablation Therapy: Model and Parameter Estimates to Predict Cell Death from MR Thermometry Images

Solid tumors and other pathologies can be treated using laser thermal ablation under interventional magnetic resonance imaging (iMRI) guidance. A model was developed to predict cell death from magnetic resonance (MR) thermometry measurements based on the temperature-time history, and validated using in vivo rabbit brain data. To align post-ablation T2-weighted spin-echo MR lesion images to gradient-echo MR images, from which temperature is derived, a registration method was used that aligned fiducials placed near the thermal lesion. The outer boundary of the hyperintense rim in the post-ablation MR lesion image was used as the boundary for cell death, as verified from histology. Model parameters were simultaneously estimated using an iterative optimization algorithm applied to every interesting voxel in 328 images from multiple experiments having various temperature histories. For a necrotic region of 766 voxels across all lesions, the model provided a voxel specificity and sensitivity of 98.1 and 78.5%, respectively. Mislabeled voxels were typically within one voxel from the segmented necrotic boundary with median distances of 0.77 and 0.22 mm for false positives (FP) and false negatives (FN), respectively. As compared to the critical temperature cell death model and the generalized Arrhenius model, our model typically predicted fewer FP and FN. This is good evidence that iMRI temperature maps can be used with our model to predict therapeutic regions in real-time during treatment.

The effect of induced hyperthermia on the immune system

Therapeutical hyperthermia has been considered for cancer therapy since William Coley observed tumour remission after induction of fever by bacterial toxins at the end of the 19th century. Because fever is associated with a variety of immunological reactions, it has been suspected, that therapeutical hyperthermia might also activate the immune system in a reproducible manner and thereby positively influence the course of the disease. During the last decade, new insight has been gained regarding the immunological changes taking place during therapeutic hyperthermia. In this chapter, we review the most relevant data known about the effect of hyperthermia on the immune system with special focus on alterations induced by therapeutical whole-body hyperthermia (WBH) in cancer patients.

Pathophysiological factors underlying heatstroke

Heatstroke is a life-threatening illness characterized by an elevated core body temperature (>40 degrees C) and dysfunction of central nervous system, which results in delirium, convulsions, or coma. Despite adequate hypothermia or other care-therapy, heatstroke is often fatal. On the basis of our knowledge of the pathophysiology on heatstroke, we hypothesized that heatstroke is a form of hyperthermia associated with the acute physiological alterations, the cytotoxicity of heat, systemic inflammatory response, oxidative damage and attenuated heat-shock response leading to a syndrome of multi-organ dysfunction. In view of above-mentioned situation, the physiological factors underlying heatstroke and the corresponding possible therapeutic strategies to avert the complications of this disorder would be summarized in this review so as to provide some therapeutic guidelines for heatstroke. Heatstroke is a very complicated process. Acute physiological alterations, such as low arterial hypotension, intracranial hypertension, cerebral hypoperfusion, cerebral ischemia, and increased intracellular metabolism rate, occurred while exposed to a high ambient temperature. Hyperpyrexia caused cytotoxicity, resulting the degradation and aggregation of extensive intracellular proteins, influencing the change of membrane stability and fluidity, damaging the transmembrane transport of protein and the function of surface receptor, and inducing different cytoskeletal changes. Heatstroke resembles sepsis in many aspects, and endotoxemia and cytokines may be implicated in its pathogenesis. The concentration of interleukin-6 was positively correlated with the severity of heatstroke. The excessive accumulation of cytotoxic free radicals and oxidative damage may occur in the brain tissues during the genesis and development of heatstroke. The circulatory shock and cerebral ischemia resultant from heatstroke correlated closely with the free radicals (especially free radicals of peroxide and superoxide), the peroxidation of lipids, and low activity of antioxidase in the brain. Heat-shock proteins (Hsps) played a critical role during the process obtaining thermotolerance, therefore, protected from stress-induce cellular damage. Host factors or physiologically limiting factors, for instance, aging, existing illness, dehydration, deep insomnia, lack of acclimation to heat, inadequate physical fitness, and certain genetic polymorphisms were associated with a low level of Hsps expression and might favor the progression from heat stress to heatstroke. Some measures, such as molecular chaperonines, anti-inflammatory agents, antioxidant agents, and modulators of Hsps would be good for the patients with heatstroke.

The relative thermal stability of tissue macromolecules and cellular structure in burn injury

When tissue is subjected to higher than physiological temperatures, protein and cell organelle structures can be altered resulting in cell death and subsequent tissue necrosis. A burn injury can be stratified into three main zones, coagulation, stasis and edema, which correlate with the extent of heat exposure and thermal properties of the tissue. While there has been considerable effort to characterize the time-temperature dependence of the injury, relatively little attention has been paid to the other important variable, the thermal susceptibility of the tissue. In the present study, we employ a standard physical chemistry approach to predict the level of denaturation at supraphysiological temperatures of 12 vital proteins as well as RNA, DNA and cell membrane components. Melting temperatures and unfolding enthalpies of the cellular components are used as input experimental parameters. This approach allows us to establish a relation between the level of denaturation of critical cellular components and clinical manifestations of the burn through the characteristic zones of the injury. Specifically, we evaluate the degree of molecular alteration for characteristic temperature profiles at two different depths (Mid-Dermis and Dermis-Fat interface) of 80 degrees C; 20s contact burn. The results of this investigation suggest that the thermal alteration of the plasma membrane is likely the most significant cause of the tissue necrosis. The lipid bilayer and membrane-bound ATPases show a high probability of thermal damage (almost 100% for the former and 85% for the latter) for short heat exposure times. These results suggest that strategies to minimize the damage in a burn injury might focus on the stabilization of the cellular membrane and membrane-bound ATPases. Further work will be required to validate these predictions in an in vivo model.

Poloxamer 188 enhances functional recovery of lethally heat-shocked fibroblasts

Damage to the cell membrane has been implicated as the primary event in the pathogenesis of heat shock, generally resulting in loss of cellular homeostasis and cell death. Thus a promising mode of therapy would involve the restoration of cell membrane integrity. Surfactant molecules, specifically triblock polymers such as Poloxamer 188 (P-188), possess the ability to self-aggregate into membrane-like structures in aqueous solutions and have been shown to restore membrane integrity. The objective of this study was to develop functional and morphological assays to determine whether treatment with P-188 after heat shock enhances the recovery of thermally damaged cells. Human foreskin fibroblasts were placed in sterile vials and heated by immersion in a calibrated water bath for various lengths of time at predefined temperatures. Cell recovery after heat shock was assessed using a functional assay based on the ability of the cells to contract fibroblast populated collagen lattices (FPCLs). Subsequent to heating, collagen lattices were prepared with control (no heat, no P-188) and heat shocked cells (with and without P-188). Our results indicate that treatment with low concentrations of P-188 after heat shock was effective in ameliorating both the morphological integrity and the contractile function of thermally damaged cells. Further, we observed that P-188 was most effective in improving the contractile ability of cells heat shocked at 45 degrees C; however, it had no influence on the contractility of cells exposed to higher temperatures. Our results suggest that there exists a threshold of thermal stress (45 degrees C for 20-60 min) beyond which treatment with low concentrations of P-188 (0.5 mg/ml) is ineffective in minimizing cell damage. Moreover, the results of our morphological assays indicate that cells treated with P-188 after heat shock maintain their cytoskeletal organization, whereas untreated cells exhibit filamentous actin depolymerization.

Diffusion theory, the cell and the synapse

The possibility exists that the cell internum is far more highly organised right down to the molecular level than was hitherto appreciated, to the point where ideas of a relatively solid-state chemistry model have been entertained (Coulson, R.A., 1993. The flow theory of enzyme kinetics--a role of solid geometry in the control reaction velocity in live animals. Int. J. Biochem. 25, 1445-1474). This contrasts sharply with the traditional dogma that diffusion is the mechanism by which molecules interact within an aqueous solution of the cell internum, although it should have been clear from an early stage that diffusion could not play other than a very restricted role in metabolic regulation. When physicists began to question certain aspects of the fundamental Law of Heat Conductance formulated over 170 years ago by Fourier, Diffusion Theory was also implicated (Maddox, J., 1989. Heat conductance is a can of worms. Nature 338, 373), and application of Fick's Laws of Diffusion to living systems criticised (Agutter P.S., Malone, P.C., Wheatley, D.N., 1995. Intracellular transport mechanisms: a critique of diffusion theory. J. Theoret. Biol. 176, 261-272). While we have argued (Wheatley, D.N., Malone, P.C., 1993. Heat conductance, diffusion theory and intracellular metabolic regulation. Biol. Cell 79, 1-5) that diffusion cannot be prevented from occurring, we found that, irrespective of whether it was a valid theory, diffusion was of little relevance in most actively metabolising cell systems. However, diffusion is still perceived as essential for interacting molecules to demonstrate their specificities. Any new model of the internal state of the living cell has to resolve this dilemma. The question also relates to molecular movement and ligand-receptor interactions outside the cell. In looking at this situation, attention was paid to one site in the body in which diffusion has long been assumed to be essential, namely in the passage of the chemical transmitter between one neurone and the next across the synaptic cleft. A detailed examination of this assumption has helped to identify one possible place in which the importance of diffusion over a distance of no more than 20-30 nm occurs, although objections to diffusion being involved have been raised. The outcome, however, only re-enforces the conviction that diffusion has little role in metabolic activity and is normally 'assisted' in almost all aspects of cell physiology.

Non-invasive, in-vivo electrical impedance of EMT-6 tumours during hyperthermia: correlation with morphology and tumour-growth-delay

The electrical impedance at frequencies from 100 Hz to 40 MHz of EMT-6 tumours was measured non-invasively, in vivo, during hyperthermia using an apparatus constructed for this purpose. Histology and morphometry were performed on tumours harvested periodically during the heating. A ratio of conductivities at two frequencies (sigma (10MHz)/sigma (10kHz)), which minimizes the tissues temperature-coefficient effects, was used to correlate impedance changes with the histopathological changes. The bulk of the cell population followed a necrotic cell death sequence during heating. Initial increase of the sigma-ratio correlated with cell swelling, and a reversal of the rate of this increase correlated with the appearance of small membrane breaks and evidence of mitochondrial damage. A continued, slowing sigma-ratio increase to a maximum correlated with continued cell swelling accompanied by increasing membrane disruption. The subsequent decrease in sigma-ratio correlated with continued general cell lysing. Between the appearance of the first membrane breaks (sigma-ratio peak) and the evidence of general lysing (sigma-ratio peak), the tumour-growth-delay increased non-linearly. Because the sigma-ratio consistently discerned these events, these measurements were able to predict the fate of this cell population when subjected to hyperthermia. Knowledge of temperature or time of heating was not required.

Response of the microtubular cytoskeleton following hyperthermia as a prognostic indicator of survival of Chinese hamster ovary cells

PURPOSE

The response of the microtubular (MT) cytoskeleton to hyperthermia was assessed as a prognostic indicator of cytotoxicity.

METHODS AND MATERIALS

Heat-induced collapse and subsequent recovery of the MT system were compared with survival for both nonthermotolerant (NT) and thermotolerant (TT) G1 populations of Chinese hamster ovary (CHO) cells. The response of the MT system was monitored using immunofluorescence staining. The G1 populations of NT and TT cells were heated by submersion in 45.0 and 43.0 degrees C waterbaths.

RESULTS

Heat-induced perinuclear collapse of the MT system did not correlate with survival for the NT and TT populations. However, recovery of the organization of the MT cytoskeleton was correlatable with survival. The regression line of survival plotted as a function of MT recovery is fit by: y = -0.43 + 1.03x, r2 = 0.95 (p < 0.0005).

CONCLUSION

Restoration of the organization of the MT cytoskeleton following hyperthermia may be used as a prognostic indicator of survival of CHO cells heated in G1.

Dynamics of cell membrane permeability changes at supraphysiological temperatures

A quantitative fluorescent microscopy system was developed to characterize, in real time, the effects of supraphysiological temperatures between 37 degrees and 70 degrees C on the plasma membrane of mouse 3T3 fibroblasts and isolated rat skeletal muscle cells. Membrane permeability was assessed by monitoring the leakage as a function of time of the fluorescent membrane integrity probe calcein. The kinetics of dye leakage increased with increasing temperature in both the 3T3 fibroblasts and the skeletal muscle cells. Analytical solutions derived from a two-compartment transport model showed that, for both cell types, a time-dependent permeability assumption provided a statistically better fit of the model predictions to the data than a constant permeability assumption. This finding suggests that the plasma membrane integrity is continuously being compromised while cells are subjected to supraphysiological temperatures.

Regulation of HSP70 and HSP28 gene expression: absence of compensatory interactions

We have previously reported the lack of HSP28 gene expression during acute and chronic thermotolerance development in L929 cells (J Cell Physiol 152: 118-125, 1992; Cancer Res 52: 5787, 1992). In contrast to HSP28, an extremely high level of inducible HSP70 synthesis was observed. These results led us to investigate the possibility of compensatory interactions between HSP70 and HSP28. To test the hypothesis, L929 cells were transfected with the human HSP28 gene contained in plasmid pCMV27. Data from Western blot and two-dimensional gel electrophoresis of [3H] leucine and [32P] orthophosphate-labeled proteins showed the synthesis and phosphorylation of HSP28 in transfected cells after heating at 45 degrees C for 10 min. However, the expression of constitutive and inducible HSP70 genes, along with the synthesis of their proteins, was not decreased after heat shock. These results suggest an independent regulation of HSP28 and HSP70 gene expression.

Spontaneous morphological changes by overexpression of the growth-associated protein B-50/GAP-43 in a PC12 cell line

In order to study the direct effects of B-50 on neural cell morphology, rat B-50 cDNA was transfected into a PC12 cell line (PC-B2) exhibiting neurite outgrowth independent of the expression of endogenous B-50. The morphological changes were visualized by confocal scanning laser microscopy using fluorescence labelling for B-50 and for F-actin. The transfected cells exhibited filopodia and/or blebs on the plasma membrane, containing most of the B-50 immunoreactivity. No spontaneous neurite outgrowth was observed. Following NGF treatment transfected and nontransfected PC-B2 cells extended F-actin positive filopodia and neurites with a striking colocalisation of B-50 and F-actin. Our data show that the presence of B-50 can influence cell surface morphology independent of the presence of NGF. The colocalisation of B-50 and F-actin in the filopodial protrusions but not in the blebs might be indicative for a role of B-50 in actin polymerization and depolymerization.

Cell death induced in L-cells by treatment with thymidine: staging of the process and relationship to apoptosis

The purpose of this study was to characterize the stages in the development of thymidine-induced cell death. L-cells were characterized by both morphologic and quantitative techniques and evaluated at 24, 48, and 72 h of treatment. Cells first enlarged (stage I); about 50% of these enlarged cells then decreased in size with blebbing and compacting (stage II). This residual cell body transformed into a smooth eosinophilic hyaline body (stage III) by 72 h, many of which could be identified within the vacuolar system of viable cells. These changes were reflected in morphologic counts and Coulter sizing. Cell death (loss of labeled DNA) began in stage II and was most prominent in stage III. No cleavage of DNA into oligonucleosomal fragments was detected by agarose gel electrophoresis at any stage. The similarity of these changes to the complete spectrum of apoptosis in vivo is discussed.

Tumor cell resistance to energy deprivation and hyperthermia can be determined by the actin skeleton stability

The effect of energy deprivation (treatment with rotenone in glucose-free medium) and hyperthermia (44 degrees C) on interphase death of EL-4 thymoma, Ehrlich and HeLa carcinomas was studied in vitro. Irreversible damage accompanied by intensive blebbing with subsequent cell death (necrosis) was observed only when elevation of actin in triton-insoluble fraction occurred although some proteins became insoluble before actin. Actin-specific drugs cytochalasin B and phalloidin accelerated both actin insolubilization and cell necrosis in rotenone-treated EL-4 cells; after conditioning treatment with recovery the actin insolubilization during hyperthermia was suppressed. Ehlrich and HeLa carcinomas were much more resistant to energy deprivation and hyperthermia; this correlated with the resistance of their actin to aggregation. It is concluded that stability of actin skeleton may be determinative of tumor cell resistance to energy deprivation, hyperthermia and possibly to some other treatments.

Plasma membrane activities retained after lethal heat shock

Cultures of Chinese hamster ovary (CHO) cells were examined to determine if heat killing could be attributed to severe damage in the plasma membrane. Three independent transport activities of the plasma membrane were measured. Glucose transport into the cells (measured with the non-metabolizable analogue 3-O-methyl-D-glucose) was stimulated rather than inhibited by heat. Most of the stimulation was found after non-toxic heat doses. Although amino acid transport (measured with the non-metabolizable analogue 2-aminoisobutyric acid) was slightly inhibited by heat, heat-sterilized cells were able to accumulate high intracellular concentrations. Cellular uptake of the nucleoside uridine was unaffected for at least 4 h after heating. In contrast, its incorporation into RNA was immediately inhibited. To further study plasma membrane damage, cells were either heated or treated with drugs which localize to the plasma membrane, ionophore A23187 or amphotericin B. The mode of cell killing by heat was radically different from that of the two drugs: heat-sterilized cells retained a phase-bright morphology and excluded the viability dye trypan blue while drug-killed cells rapidly became phase-dark and absorbed the dye. These results add to a growing list of plasma membrane activities which are retained in heat-sterilized cells, and suggest that the initial thermal damage responsible for cell killing is at an alternate site(s).

Two different pathways for necrotic cell death induced by free radicals

Plasma membrane modifications have been widely recognized as crucial factors in cell injury and death. One of these modifications, surface blebbing, has been considered as an injury-marker associated with a series of biochemical and physiological modifications. Our study focused on the different effects of free radical-induced cell damage by quinone menadione (2-methyl-1,4-naphthoquinone) and by hyperthermic shock (45 degrees C) on the erythroleukemic cell line K562. Different techniques including immunofluorescence, freeze-fracturing, and electron paramagnetic resonance spectroscopy were employed. Menadione induced the formation of surface blebs, accompanied by a rearrangement of the microfilament system and changes in the distribution of plasma membrane proteins. In contrast, heat-shocked cells showed neither blebbing nor important cytoskeletal changes. Finally, the electron paramagnetic resonance results showed an increase in membrane order not specifically related to the type of free radical-induced stress. These cell death features appear to suggest the existence of two different types of pathways for necrotic cell death: both treatments induce cell injury and eventual death by modifying plasma membrane integrity and function. However, one involves cytoskeleton-dependent surface blebbing, whereas the other does not.

Changes in electrical impedance of skeletal muscle measured during hyperthermia

The electrical impedance of rat skeletal muscle was measured from 100 Hz to 40 MHz during the application of typical hyperthermia heating regimens. Trials were performed employing freshly excised tissue heated to target temperatures from 39.5 to 50 degrees C. Abrupt and rapid decreases in the low-frequency beta-dispersion occurred very shortly after reaching hyperthermia temperatures. These rapid decreases continued at a rate and to an extent dependent upon the target temperature, and then, as heating continued, abruptly changed to a much slower rate which continued indefinitely. The initial rapid changes were associated with microscopically observed muscle fibre rounding and radial shrinkage, with accompanying increasing interstitial oedema. The subsequent slow changes were associated with a slow histolysis. The time- and temperature-dependence of the rapid resistivity changes evidenced similarities to typical hyperthermia endpoint responses. An Arrhenius analysis of the rate of the resistivity changes yielded a break at 43 degrees C, with activation energies of 36.1 and 58.3 kcal/mol above and below this break. Preliminary in vivo impedance data displayed qualitative similarities to the excised tissue findings.

Content of nonhistone protein in nuclei after hyperthermic treatment

When nuclei were isolated from Chinese hamster ovary cells after being heated, there was a large increase in the amount of 3H-tryptophan labeled nonhistone protein in the nucleus relative to the whole cell. After 15 min or 30 min of heating at 45.5 degrees C, the nuclear nonhistone protein content increased by 1.6 or 1.8, respectively. In contrast, when the nuclear nonhistone protein content was determined in the intact cell by using autoradiography to quantify 3H-tryptophan labeled protein in the nucleus and cytoplasm in sections of fixed cells, the nuclear nonhistone protein content increased by only 1.14 or 1.28 for 15 or 30 min at 45.5 degrees C, respectively. Therefore, heat does not induce a massive movement of cytoplasmic protein into the nucleus.

Cell surface extensions associated with overexpression of Alzheimer beta/A4 amyloid

Deposition of beta/A4 amyloid in Alzheimer disease (AD) brain parenchyma and vasculature occurs by mechanisms that are currently undefined. Similarly the potential consequences of amyloid accumulation for disrupting cellular integrity have not been addressed in detail. To investigate the possible significance of amyloid deposits for cellular viability, PC12 cells were permanently transfected with DNA coding for the beta/A4-C terminal region of the amyloid precursor protein. The DNA represented 97 amino acids of the amyloid precursor protein of which 40 amino acids were derived from the beta/A4 region. Transfected clonal cell lines and controls were examined at both the light and electron microscopic levels for morphological abnormalities. beta/A4 amyloid accumulated in the cell membrane where the peptide was located at cellular processes resembling blebs and microvilli. These specialized structures at the cell surface were over-abundant in transfected cells that overexpressed the beta/A4 peptide but not in controls. Membranous processes may be involved in the delivery of the beta/A4 peptide to the external surface of the cell of origin and release into the extracellular space. Similar surface features of cells in the AD brain, should they occur, may indicate a role for membrane-associated processes in the pathophysiology of the disorder.

Cycloheximide protection against actinomycin D cytotoxicity

Pretreatment plus concomitant treatment with 10 micrograms/ml cycloheximide protected Chinese hamster ovary cells and Swiss 3T3 cells against the cytotoxicity of actinomycin D. The cycloheximide treatment reduced the intracellular concentration of actinomycin D by reducing the level of actinomycin D bound to the acid precipitable fraction of the cell. Levels of unbound actinomycin D were unaffected by cycloheximide, indicating that the plasma membrane permeability to AD was not reduced. Actinomycin D inhibited total transcription but did not reduce cytoplasmic levels of rRNA nor of most tested mRNA; however, cytoplasmic levels of c-myc mRNA were reduced below detectability. Cycloheximide treatment further inhibited total transcription and had no effect on cytoplasmic levels of rRNA nor of most tested mRNA. Cytoplasmic levels of c-myc were elevated by cycloheximide and remained so even in the presence of actinomycin D. These data suggested that a reduction in cytoplasmic levels of short lived, essential mRNA, such as c-myc mRNA, was one lethal lesion of actinomycin D. Furthermore, cycloheximide's protection may result, in part, from its ability to stabilize and/or elevate cytoplasmic levels of these mRNA, thus counteracting their depletion by actinomycin D. Protection may also result from the cycloheximide-induced reduction of actinomycin D bound to the acid precipitable fraction of the cells.

Cytoskeleton-dependent surface blebbing induced by the polar solvent N-methylformamide

In vivo and in vitro studies performed on the polar solvent N-methylformamide (NMF), as well as on its association with chemotherapeutic agents or X rays, have clearly demonstrated that this compound is capable of inducing changes in biological characteristics of tumor cells, e.g., cell differentiation. However, the mechanism of action of NMF is far from being elucidated. Hence, in order to better clarify such a mechanism an in vitro study was carried out by using mouse fibroblasts in primary culture (MEF) and human melanoma cultured cells (M14). Results obtained by immunocytochemical and ultrastructural methods with doses of NMF ranging from 0.1 to 7% are reported here. As a general rule, a different sensitivity (in terms of cytopathologic changes induced by NMF) was found between the cell types considered. In fact, melanoma cells appeared to be highly susceptible to the action of the drug, undergoing severe morphological modifications represented mainly by a reversible dose and time-dependent cell rounding and surface blebbing. In contrast, NMF-induced injury in MEF cells was characterized mainly by a simple retraction of the cell body. A cytochemical analysis of the expression of certain membrane antigens (e.g., glycoproteins, epidermal growth factor receptor, B2 microglobulin) in NMF-treated M14 cells undergoing blebbing was also carried out. A randomly distributed labeling of such molecules was observed. Accordingly, freeze-fracturing electron microscopic analysis also displayed a random distribution of intramembrane particles over the plasma membrane. When subcellular changes induced by the drug were investigated, a remarkable modification of cytoskeletal components was detected in both cell types. In particular, cross-linked actin microfilament bundles were easily observed in NMF-exposed MEF cells. Finally, when different experimental conditions which perturb calcium ion homeostasis or restore protein thiol group reduced state were analyzed, a noticeable impairment of the blebbing phenomenon was observed. Thus, a target effect of NMF on the microfilament system, probably leading, in turn, to several subcellular changes and cell surface blebbing, can be hypothesized. Such a cytoskeletal element-dependent cytopathology appears to be related to changes of the oxidized state of such molecules as well as to calcium ion perturbations.

Heat-resistant variants of the Chinese hamster ovary cell: alteration of cellular structure and expression of vimentin

Three heat-resistant mutant cell lines (78-1, 78-2, 78-3) were previously selected from Chinese hamster ovary cells. In this study, we investigated whether the differences in intrinsic thermal sensitivity result from alteration of stress protein levels or cellular structural changes. Although there was no significant difference in the levels of stress proteins, i.e., constitutive HSP70 in wild type and three heat-resistant mutant strains, there were marked differences in the amounts of vimentin among the cell lines. Two-dimensional gel electrophoresis and Western blot showed a 2.3-2.9-fold increase in the level of vimentin in the mutant cells under normal growth conditions. Northern blot also revealed higher amounts of vimentin mRNA in the mutant cells. Electron microscopy and immunofluorescence suggest that increased amounts of the vimentin-containing intermediate filaments are correlated with the heat-resistant phenotypes.

Association of blebbing with assembly of cytoskeletal proteins in ATP-depleted EL-4 ascites tumour cells

ATP depletion in EL-4 ascites tumour cells rapidly induced the changes in cell morphology (blebbing), cytoskeletal protein assembly and finally resulted in cell death. After 1 hr of incubation with 2 microM rotenone (inhibitor of respiration) in glucose-free medium, when ATP level was 4% of the initial level, there were increases in triton-insoluble actin and vinculin levels (2.5-fold and 2.8-fold, respectively) and 44% of cells showed blebs; such treatment damaged cells irreversibly. Ca2+ removal did not diminish the effect of ATP depletion on cytoskeleton, blebbing and cell death, although the elevation of free intracellular Ca2+ in rotenone-treated cells was prevented. The role of ATP in maintaining cytoskeleton and cell shape is discussed.

Electroporation of extraneous proteins into CHO cells: increased efficacy by utilizing centrifugal force and microsecond electrical pulses

A novel electroporation system employing an oscillating electric pulse and centrifugal force was used to introduce extraneous proteins into CHO cells. Following the electrical pulse, the compression and subsequent rebound induced by the centrifugal acceleration and deceleration, respectively, enhanced protein uptake, presumably by a hydrodynamic pumping of extracellular solutions through the permeabilized membrane. Protein uptake was quantitated by measuring the amount of radiolabeled, extraneous, CHO proteins introduced into unlabeled CHO cells. The amount of protein introduced into electroporated CHO cells was enhanced up to four-fold by a combination of electric pulse and centrifugal force compared to that introduced by electric pulse only. The optimum gradient of centrifugal force (GCF, temporal change of centrifugal force) was 590 and -470 g/s during acceleration and deceleration, respectively. The optimum electric field was 5 kV/cm with a 30-microsecond pulse length. At this optimum electroporation condition, approximately 5 pg of proteins (up to 200 kDa molecular weight) were introduced per CHO cell. These same settings also permitted electroporation of other membrane impermeable substances including propidium iodide and ethidium bromide. Introduction of extraneous materials into the cytoplasm during electroporation was confirmed by the ability of anti alpha-tubulin to stain the microtubules and propidium iodide and ethidium bromide to stain the nuclei. Cells electroporated with optimum device settings exhibited no significant decrease in clonogenic survival.

Microelectrode measurements of the transmembrane potential in baby hamster kidney, (Chinese hamster ovary), NG108-15 neuroblastoma and Swiss 3T3 cells at 37.0 or 43.0 degrees C

Hyperthermia affects the physical state and function of the plasma membrane. This could alter the transmembrane potential (Vm) and associated functions in a manner that promotes cell killing. Previous investigations have reported differing results of the effect of heat on Vm, possibly due to artifacts associated with the methods employed to measure Vm indirectly. One such artifact is a membrane depolarization induced by cationic probes, as demonstrated in this paper. In this study, glass microelectrodes were used to avoid these artifacts and to make direct electrical measurements of Vm. Following 25 min-30 min at 43.0 degrees C, The mean Vm of Chinese hamster ovary (CHO) cells, within clusters of six or more cells, decreased from -16 +/- 5 to -38 +/- 6 mV, and remained at these levels during incubation times up to 3 h. All CHO cells resumed a normal Vm within 4.5 h after returning to 37.0 degrees C, regardless of the time of exposure at 43.0 degrees C (0.5 to 3.0 h, with survival levels of 0.7 and 0.001, respectively). The membrane hyperpolarization decreased with cell to cell contact to where isolated cells exhibited no hyperpolarization. CHO cultures with different cell densities (number of cells per cm2), and thus differing degrees of cell to cell contact, were heated and then subjected to the colony formation assay. The degree of cell to cell contact at the time of heating had no effect on survival. Hence, the heat-induced, cell contact dependent hypolarization of CHO cell membranes was unrelated to clonogenic survival.(ABSTRACT TRUNCATED AT 250 WORDS)

Cycloheximide increases the thermostability of proteins in Chinese hamster ovary cells

Protein denaturation resulting from temperatures between 42.0 degrees C and 50 degrees C has been observed and implicated as the lethal lesion for hyperthermic cell killing. A logical corollary is that protection against hyperthermic killing requires stabilization of cellular proteins against thermal denaturation. To test this, Chinese hamster ovary cells were treated with the heat protector cycloheximide and then subjected to differential scanning calorimetry to measure protein denaturation. Cycloheximide stabilized proteins that denatured between 42 degrees C and 52 degrees C in control cells by increasing their transition (denaturation) temperature by an average of 1.3 degrees C. In addition, cycloheximide reduced the cytotoxicity of actinomycin D and adriamycin, suggesting that protein stabilization protects cells against stresses other than hyperthermia.

Sensitization to hyperthermia by 3,3'-dipentyloxacarbocyanine iodide: a positive correlation with DNA damage and negative correlations with altered cell morphology, oxygen consumption inhibition, and reduced ATP levels

The cyanine dye 3,3'-dipentyloxacarbocyanine iodide (DiOC5(3)) (concentrations of 0.5 microgram/ml to 5.0 micrograms/ml) was shown to be a potent sensitizer of Chinese hamster ovary (CHO) cells to hyperthermic cell killing at 43.0 degrees C or 45.5 degrees C, while exhibiting no cytotoxicity at 37.0 degrees C. Sensitization to hyperthermic cell killing was accompanied by an increase in damage to the DNA, as measured by DNA unwinding. The increased DNA damage correlated qualitatively with the enhanced heat killing induced by DiOC5(3). This correlation was better in cells heated at 43.0 degrees C than in those heated at 45.5 degrees C. DiOC5(3) is known to affect other cellular functions. It inhibits electron transport, uncouples oxidative phosphorylation, and inhibits calcium ATPases. The effects of DiOC5(3) on oxygen consumption and ATP content were therefore measured at 37.0 degrees C and at hyperthermic temperatures. The results demonstrated that inhibition of oxygen consumption and reduction of cellular ATP levels played no role in inducing heat sensitization in DiOC5(3)-treated cells, or in causing cell death in cells treated with heat alone.

Cytoskeleton as a target in menadione-induced oxidative stress in cultured mammalian cells: alterations underlying surface bleb formation

Several in vitro and in vivo studies have suggested that surface bleb formation during oxidative cell injury is related to alteration in cytoskeleton organization. Various cell lines different in origin and growth characteristics were exposed to 2-methyl-1,4-naphthoquinone (menadione) which is known to induce bleb formation and cytotoxicity by generating considerable amounts of oxygen-reactive species. Treated cells were analyzed by means of immunocytochemistry and electron microscopy in order to investigate the morphological and molecular features underlying bleb generation. The results obtained indicate that menadione-induced bleb formation is a widely observed phenomenon present mainly in round or mitotic cells. Surface blebs appear free of organelles and contain only few ribosomes and amorphous material. Occasionally, they undergo detachment from the cell surface as large cytoplasmic vesicles. Bleb surfaces with protein clusters as well as bald blisters with an almost exclusive localization of intramembrane particles on their narrow base were detected using freeze-fracture techniques. Immunocytochemical investigations performed on menadione-exposed cells revealed that some surface proteins (collagen IV, sialo-proteins, beta 2 microglobulin and fibronectin) and adhesion molecules (vinculin) underwent changes in their expression over the bleb surface. Moreover, different behavioural characteristics of actin microfilaments, vimentin and keratin intermediate filaments and microtubules was observed. Alpha-actinin, vimentin and microtubular proteins (tubulin, MAPs and tau) were detected within the blebs. On the other hand, actin and keratin filaments appeared to be absent. The results presented here demonstrate that cytoskeletal structures and the microfilament system in particular, represent important targets in menadione-induced morphological changes in cultured cells. These changes appear to lead to the redistribution of several cytoskeletal and membrane proteins as well as dissociation of the cytoskeleton network from its anchoring domains in the plasma membrane thus generating sites of structural weakness where blebs would arise and progressively grow. Experimental evidence supporting a crucial role of thiol oxidation and elevation of cytoplasmic calcium concentration in bleb formation is also provided.

Hyperthermia-induced shedding and masking of melanoma-associated antigen

Hyperthermia has been reported to induce a dose-dependent reduction in the expression of melanoma-associated surface antigens. The objective of the present work was to study the mechanisms for the reduction in the expression of the p250 antigen recognized by the monoclonal antibody 9.2.27. Measurements at 37 degrees C showed that antibody binding induced a certain degree of modulation (internalization) of the melanoma-associated antigen. Masking of the antigen due to internalization and/or damage in situ, as well as shedding of the antigen, were measured after hyperthermia, and found to increase in a heat-dose-dependent manner, although for antigen masked this increase was not significant compared with control cells at 37 degrees C. The sum of antigen shed and masked after hyperthermia correlated with the overall reduction in antigen expression measured independently. During hyperthermia, antigen was shed and masked in approximately equal amounts. After the treatment, hyperthermia-induced shedding continued as a function of time and caused a further reduction in antigen expression, but masking did not differ from 37 degrees C controls.

Time-temperature analysis of cell killing of BHK cells heated at temperatures in the range of 43.5 degrees C to 57.0 degrees C

Baby hamster kidney (BHK) cells were heated at temperatures in the range of 43.5 degrees C to 57.0 degrees C to determine the time-temperature relationship of cell killing. The cells were grown on 0.025 mm thick pieces of mylar to minimize warm-up times. After heating, the cells were plated for the colony formation assay. The endpoints of 1%, 10%, or 90% isosurvival, or the D0 values of the survival curves were used to construct plots of the logarithm of the reciprocol of the exposure time versus the reciprocol of the absolute temperature. The data for each endpoint resulted in a straight line plot, indicating that the time-temperature relationship for cell killing remained constant from 43.5 degrees C to 57.0 degrees C; namely, a 1.8-fold increase in exposure time was required for a 1 degree C decrease in temperature in order to obtain isosurvival. Heated BHK cells were also examined using electron microscopy. The threshold level of altered morphology was the dissociation of polyribosomal structure and the formation of electron-dense granules within the mitochondria. The time-temperature relationship for the induction of this altered morphology was identical to that for the 90% isosurvival endpoint. Hence, the appearance of altered morphology appears to be related to cell killing.

Methods for determination of growth-rate-dependent changes in hybridoma volume, shape and surface structure during continuous recycle

Hybridoma volume and surface membrane structure were found to vary as a function of specific growth rate using a method of cell recycle with continuous medium perfusion to vary growth rate. Mean hybridoma volume determined at constant osmolality by both electronic particle counting and scanning electron microscopic (SEM) methods indicated that rapidly growing cells are significantly larger than very slowly growing cells. We have previously determined that during both rapid and slow growth over a range of L-glutamine provision rates (Gln PR) that specific monoclonal antibody (MoAb) secretion rate was not changed. In this study a constant MoAb secretion rate per unit of membrane area was found which may indicate that changing membrane area is not a rate-determining factor in MoAb secretion. SEM methods were of limited use for accurate determination of cell volume due to cell shrinkage and large coefficients of variations. In spite of this limitation, SEM stereology methods were useful in confirming that cells remained spherical over a wide range of specific growth rates and that hybridoma cells were not circular. Sequential SEM observations also revealed that surface membrane structure of the 9.2.27 murine hybridoma investigated was correlated with growth rate. Under conditions of very slow growth, hybridoma surface microvilli density appeared to be significantly reduced.

Surface blebbing and cytoskeletal changes induced in vitro by toxin B from Clostridium difficile: an immunochemical and ultrastructural study

Clostridium difficile toxin B is a powerful cytopathic agent without enterotoxic activity which is believed to be involved in the pathogenesis of pseudomembranous colitis. Up until today, the mechanisms of toxin B cytotoxicity have not been elucidated. The results of in vitro studies performed on different cell lines by means of immunocytochemical and ultrastructural methods are reported here. Low doses (0.15 ng/ml) of toxin B cause cell rounding and arborization. Higher doses (up to 15 micrograms/ml) induce cell rounding and appearance of numerous surface protrusions with blister or bulb-like features. These "blebs" belong to the potocytotic type, the bleb matrix being devoid of cytoplasmic organelles and filled with ribosomes only. Furthermore, a peculiar role of cytoskeletal apparatus in this phenomenon has been detected. In fact, morphological rearrangement occurs in cytoskeletal elements, mainly represented by the presence, in the blebs, of tubulin and of the actin-binding proteins alpha-actinin, filamin, and calmodulin, while actin and intermediate filaments, keratin and vimentin, appear to be absent. Moreover, beta 2-microglobulin, considered as a surface protein marker, seems to undergo changes in its expression, being absent over the blebbing surface. The results of this study may support the view that C. difficile toxin B affects one or more subcellular components that regulate the structure and function of the actin cytoskeleton.

Interaction of free fatty acids with the erythrocyte membrane as affected by hyperthermia and ionizing radiation

The interference of hyperthermia and ionizing radiation, respectively, with the effects of capric (10:0), lauric (12:0), myristic (14:0), oleic (cis-18:1) and elaidic (trans-18:1) acids on the osmotic resistance of human erythrocytes was investigated. The results are summarized as follows: (A) not only at 37 degrees, but also at 42 degrees and 47 degrees C lauric acid (12:0) represents the minimum chain length for the biphasic behaviour of protecting against hypotonic hemolysis at a certain lower concentration range and hemolysis promotion at subsequent higher concentrations; (B) with increasing temperatures the protecting as well as the hemolytic effects occur at lower concentrations of the fatty acids; (C) the increase of temperature promotes the extent of hemolysis and reduces the extent of protection against hypotonic hemolysis; (D) Gamma-irradiation of erythrocytes selectively affects the concentration of oleic acid at which maximum protection against hypotonic hemolysis occurs, without altering the minimum concentration for 100% hemolysis.