Heat shock- and ethanol-induced ionic changes in C6 rat glioma cells determined by NMR and fluorescence spectroscopy

Controlled radio-frequency hyperthermia using an MR scanner and simultaneous monitoring of temperature and therapy response by (1)H, (23)Na and (31)P magnetic resonance spectroscopy in subcutaneously implanted 9L-gliosarcoma

A magnetic resonance (MR) technique is developed to produce controlled radio-frequency (RF) hyperthermia (HT) in subcutaneously-implanted 9L-gliosarcoma in Fisher rats using an MR scanner and its components; the scanner is also simultaneously used to monitor the tumour temperature and the metabolic response of the tumour to the therapy. The method uses the (1)H chemical shift of thulium 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetra-acetic acid (TmDOTA(-)) to monitor temperature. The desired HT temperature is achieved and maintained using a feedback loop mechanism that uses a proportional-integral-derivative controller. The RF HT technique was able to heat the tumour from 33 degrees to 45 degrees C in approximately 10 min and was able to maintain the tumour temperature within +/-0.2 degrees C of the target temperature (45 degrees C). Simultaneous monitoring of the metabolic changes with RF HT showed increases in total tissue and intracellular Na(+) as measured by single-quantum and triple-quantum filtered (23)Na MR spectroscopy (MRS), respectively, and decreases in intra- and extracellular pH and cellular bioenergetics as measured by (31)P MRS. Monitoring of metabolic response in addition to the tumour temperature measurements may serve as a more reliable and early indicator of therapy response. In addition, such measurements during HT treatment will enhance our understanding of the tumour response mechanisms during HT, which may prove valuable in designing methods to improve therapeutic efficiency.

Exertional heat illness and human gene expression

Microarray analysis of gene expression at the level of RNA has generated new insights into the relationship between cellular responses to acute heat shock in vitro, exercise, and exertional heat illness. Here we discuss the systemic physiology of exertional hyperthermia and exertional heat illness, and compare the results of several recent microarray studies performed in vitro on human cells subjected to heat shock and in vivo on samples obtained from subjects performing exercise or suffering from exertional heat injury. From these comparisons, a concept of overlapping component responses emerges. Namely, some of the gene expression changes observed in peripheral blood mononuclear cells during exertional heat injury can be accounted for by normal cellular responses to heat, exercise, or both; others appear to be specific to the disease state itself. If confirmed in future studies, these component responses might provide a better understanding of adaptive and pathological responses to exercise and exercise-induced hyperthermia, help find new ways of identifying individuals at risk for exertional heat illness, and perhaps even help find rational molecular targets for therapeutic intervention.

Effects of temperature on intracellular sodium, pH and cellular energy status in RIF-1 tumor cells

Most perfused tumor cell experiments are performed at 37 degrees C, the normal healthy body temperature. However, the temperature of subcutaneously implanted tumors in small animals is generally 29-33 degrees C when the rectal temperature of the animal is maintained at 37 degrees C. We have investigated the acute effects of increasing the temperature of perfused radiation-induced-fibrosarcoma (RIF-1) tumor cells from 33 to 37 degrees C (30 min) on intracellular sodium (Na(i)+) , intracellular pH (pH(i)), and bioenergetic status. Heating the cells by 4 degrees C produced a reversible increase in Na(i)+, slight acidification and no change in nucleotide triphosphate to inorganic phosphate ratio (NTP/P(i)) as measured by shift-reagent-aided (23)Na and (31)P NMR spectroscopy. In the presence of 3 microM 5-(N-ethyl-N-isopropyl) amiloride (EIPA), a potent and specific inhibitor of Na(+)/H(+) antiporter, the increase in Na(i)+ during the heating was completely abolished suggesting that the heat induced increase in Na(i)+ was caused by an increase in Na(+)/H(+) antiporter activity. However, the changes in pH(i) with the heating were identical with or without EIPA, indicating that pH(i) is controlled by other ion exchange mechanisms in addition to Na(+)/H(+) antiporter. NTP/P(i) was significantly higher in presence of EIPA for some time points during the heating suggesting that both NTP production and consumption rates may be altered during the heating. These results indicate that a slight increase in temperature from 33 to 37 degrees C induces significant changes in Na(+) physiology largely because of activation of Na(+)/H(+) antiporter but other ion exchange mechanisms are also involved in maintaining pH(i) in the RIF-1 tumor cells. Thus, care must be taken in choosing the temperature for perfused cell studies.

Temperature effect on entrainment, phase shifting, and amplitude of circadian clocks and its molecular bases

Effects of temperature and temperature changes on circadian clocks in cyanobacteria, unicellular algae, and plants, as well as fungi, arthropods, and vertebrates are reviewed. Periodic temperature with periods around 24 h even in the low range of 1-2 degrees C (strong Zeitgeber effect) can entrain all ectothermic (poikilothermic) organisms. This is also reflected by the phase shifts-recorded by phase response curves (PRCs)-that are elicited by step- or pulsewise changes in the temperature. The amount of phase shift (weak or strong type of PRC) depends on the amplitude of the temperature change and on its duration when applied as a pulse. Form and position of the PRC to temperature pulses are similar to those of the PRC to light pulses. A combined high/low temperature and light/dark cycle leads to a stabile phase and maximal amplitude of the circadian rhythm-when applied in phase (i.e., warm/light and cold/dark). When the two Zeitgeber cycles are phase-shifted against each other the phase of the circadian rhythm is determined by either Zeitgeber or by both, depending on the relative strength (amplitude) of both Zeitgeber signals and the sensitivity of the species/individual toward them. A phase jump of the circadian rhythm has been observed in several organisms at a certain phase relationship of the two Zeitgeber cycles. Ectothermic organisms show inter- and intraspecies plus seasonal variations in the temperature limits for the expression of the clock, either of the basic molecular mechanism, and/or the dependent variables. A step-down from higher temperatures or a step-up from lower temperatures to moderate temperatures often results in initiation of oscillations from phase positions that are about 180 degrees different. This may be explained by holding the clock at different phase positions (maximum or minimum of a clock component) or by significantly different levels of clock components at the higher or lower temperatures. Different permissive temperatures result in different circadian amplitudes, that usually show a species-specific optimum. In endothermic (homeothermic) organisms periodic temperature changes of about 24 h often cause entrainment, although with considerable individual differences, only if they are of rather high amplitudes (weak Zeitgeber effects). The same applies to the phase-shifting effects of temperature pulses. Isolated bird pineals and rat suprachiasmatic nuclei tissues on the other hand, respond to medium high temperature pulses and reveal PRCs similar to that of light signals. Therefore, one may speculate that the self-selected circadian rhythm of body temperature in reptiles or the endogenously controlled body temperature in homeotherms (some of which show temperature differences of more than 2 degrees C) may, in itself, serve as an internal entraining system. The so-called heterothermic mammals (undergoing low body temperature states in a daily or seasonal pattern) may be more sensitive to temperature changes. Effects of temperature elevation on the molecular clock mechanisms have been shown in Neurospora (induction of the frequency (FRQ) protein) and in Drosophila (degradation of the period (PER) and timeless (TIM) protein) and can explain observed phase shifts of rhythms in conidiation and locomotor activity, respectively. Temperature changes probably act directly on all processes of the clock mechanism some being more sensitive than the others. Temperature changes affect membrane properties, ion homeostasis, calcium influx, and other signal cascades (cAMP, cGMP, and the protein kinases A and C) (indirect effects) and may thus influence, in particular, protein phosphorylation processes of the clock mechanism. The temperature effects resemble to some degree those induced by light or by light-transducing neurons and their transmitters. In ectothermic vertebrates temperature changes significantly affect the melatonin rhythm, which in turn exerts entraining (phase shifting) functions.

Effect of acute heat shock on gene expression by human peripheral blood mononuclear cells

We studied the effect of heat shock on gene expression by normal human cells. Peripheral blood mononuclear cells (PBMCs) were obtained from healthy adults. Paired samples from each subject were subjected to either 20 min of heat shock (43 degrees C) or control (37 degrees C) conditions and then returned to 37 degrees C. RNA was isolated 160 min later, and five representative samples were analyzed on Affymetrix gene chip arrays containing approximately 12,600 probes. A biologically meaningful effect was defined as a statistically significant, twofold or greater difference in expression of sequences that were detected in all five experiments under control (downregulated sequences) or heat shock (upregulated sequences) conditions. Changes occurred in 395 sequences (227 increased by heat shock, 168 decreased), representing 353 Unigene numbers, in every functional category previously implicated in the heat shock response. By RT-PCR, we confirmed the findings for one upregulated sequence (Rad, a G protein) and one downregulated sequence (osteopontin, a cytokine). We conclude that heat shock causes extensive gene expression changes in PBMCs, affecting all functional categories of the heat shock response.

Heat shock protein induction by certain chemical stressors is correlated with their cytotoxicity, lipophilicity and protein-denaturing capacity

Seven agents were analyzed with respect to their ability to induce heat shock protein (HSP) synthesis in C6 rat glioma cells. Induction of HSP synthesis was correlated with cytotoxicity and lipophilicity of the substances. In addition to the first four n-alcohols (methanol, ethanol, propanol and butanol) and phenol, whose capacity to induce HSP was analyzed earlier (Neuhaus-Steinmetz et al., 1994. Mol. Pharmacol. 45, 36-41), isopropanol, 1,4-dinitrophenol (DNP), diethylstilbestrol (DES), carbonylcyanide-m-chlorophenylhydrazone (CCCP), rotenone, paracetamol and acetyl salicylic acid (ASA) induced HSP synthesis after a 1-h incubation at a substance-specific concentration. The maximal induction of HSPs was closely correlated with the cytotoxicity of all substances and occurred when cell viability was reduced to 75 +/- 11% of the controls. Cytotoxicity and the ability to induce HSP were correlated with the lipophilicity of the alcohols, phenol, rotenone and paracetamol. Calculation of the hypothetical membrane concentrations of these compounds yielded a nearly equal value (0.54 +/- 0.13 M), indicating that interaction of substances with lipophilic cellular compounds, such as membranes or lipophilic core regions of proteins, is a critical step leading to HSP induction. This assumption is supported by a correlation between HSP induction and protein denaturation by the different alcohols (Herskovits et al., 1970. J. Biol. Chem. 245, 2588-2598). We assume that the amount of misfolded proteins induced by these lipophilic agents is responsible for the induction of HSP synthesis. ASA, DNP and CCCP induced HSP at lower concentrations than substances with a similar lipophilicity, which may be due to effects which add to the misfolding of proteins or to other signal pathways.