Temperature-induced homeoviscous adaptation of Chinese hamster ovary cells

Pharmacokinetics during therapeutic hypothermia in neonates: from pathophysiology to translational knowledge and physiologically-based pharmacokinetic (PBPK) modeling

INTRODUCTION

Perinatal asphyxia (PA) still causes significant morbidity and mortality. Therapeutic hypothermia (TH) is the only effective therapy for neonates with moderate to severe hypoxic-ischemic encephalopathy after PA. These neonates need additional pharmacotherapy, and both PA and TH may impact physiology and, consequently, pharmacokinetics (PK) and pharmacodynamics (PD).

AREAS COVERED

This review provides an overview of the available knowledge in PubMed (until November 2022) on the pathophysiology of neonates with PA/TH. In vivo pig models for this setting enable distinguishing the effect of PA versus TH on PK and translating this effect to human neonates. Available asphyxia pig models and methodological considerations are described. A summary of human neonatal PK of supportive pharmacotherapy to improve neurodevelopmental outcomes is provided.

EXPERT OPINION

To support drug development for this population, knowledge from clinical observations (PK data, real-world data on physiology), preclinical (in vitro and in vivo (minipig)) data, and molecular and cellular biology insights can be integrated into a predictive physiologically-based PK (PBPK) framework, as illustrated by the I-PREDICT project (Innovative physiology-based pharmacokinetic model to predict drug exposure in neonates undergoing cooling therapy). Current knowledge, challenges, and expert opinion on the future directions of this research topic are provided.

The Effects of Temperature on Cellular Physiology

Temperature impacts biological systems across all length and timescales. Cells and the enzymes that comprise them respond to temperature fluctuations on short timescales, and temperature can affect protein folding, the molecular composition of cells, and volume expansion. Entire ecosystems exhibit temperature-dependent behaviors, and global warming threatens to disrupt thermal homeostasis in microbes that are important for human and planetary health. Intriguingly, the growth rate of most species follows the Arrhenius law of equilibrium thermodynamics, with an activation energy similar to that of individual enzymes but with maximal growth rates and over temperature ranges that are species specific. In this review, we discuss how the temperature dependence of critical cellular processes, such as the central dogma and membrane fluidity, contributes to the temperature dependence of growth. We conclude with a discussion of adaptation to temperature shifts and the effects of temperature on evolution and on the properties of microbial ecosystems.

Hypometabolic Responses to Chronic Hypoxia: A Potential Role for Membrane Lipids

Metabolic suppression is an essential strategy to cope with chronic hypoxia. This review examines the physiological processes used to survive in low oxygen environments. It proposes a novel mechanism-the remodeling of membrane lipids-to suppress ATP use and production. Temperature (homeoviscous adaptation), diet (natural doping in migrant birds) and body mass (membrane pacemaker of metabolism) have an impact on the lipid composition of membranes, which, in turn, modulates metabolic capacity. Vertebrate champions of hypoxia tolerance show extensive changes in membrane lipids upon in vivo exposure to low oxygen. These changes and those observed in hibernating mammals can promote the downregulation of ion pumps (major ATP consumers), ion channels, mitochondrial respiration capacity (state 3, proton leak, cytochrome c oxidase), and energy metabolism (β-oxidation and glycolysis). A common membrane signal regulating the joint inhibition of ion pumps and channels could be an exquisite way to preserve the balance between ATP supply and demand in hypometabolic states. Membrane remodeling together with more traditional mechanisms could work in concert to cause metabolic suppression.

TRP Channels as Sensors of Chemically-Induced Changes in Cell Membrane Mechanical Properties

Transient Receptor Potential ion channels (TRPs) have been described as polymodal sensors, being responsible for transducing a wide variety of stimuli, and being involved in sensory functions such as chemosensation, thermosensation, mechanosensation, and photosensation. Mechanical and chemical stresses exerted on the membrane can be transduced by specialized proteins into meaningful intracellular biochemical signaling, resulting in physiological changes. Of particular interest are compounds that can change the local physical properties of the membrane, thereby affecting nearby proteins, such as TRP channels, which are highly sensitive to the membrane environment. In this review, we provide an overview of the current knowledge of TRP channel activation as a result of changes in the membrane properties induced by amphipathic structural lipidic components such as cholesterol and diacylglycerol, and by exogenous amphipathic bacterial endotoxins.

To flourish or perish: evolutionary TRiPs into the sensory biology of plant-herbivore interactions

The interactions between plants and their herbivores are highly complex systems generating on one side an extraordinary diversity of plant protection mechanisms and on the other side sophisticated consumer feeding strategies. Herbivores have evolved complex, integrative sensory systems that allow them to distinguish between food sources having mere bad flavors from the actually toxic ones. These systems are based on the senses of taste, olfaction and somatosensation in the oral and nasal cavities, and on post-ingestive chemosensory mechanisms. The potential ability of plant defensive chemical traits to induce tissue damage in foragers is mainly encoded in the latter through chemesthetic sensations such as burning, pain, itch, irritation, tingling, and numbness, all of which induce innate aversive behavioral responses. Here, we discuss the involvement of transient receptor potential (TRP) channels in the chemosensory mechanisms that are at the core of complex and fascinating plant-herbivore ecological networks. We review how "sensory" TRPs are activated by a myriad of plant-derived compounds, leading to cation influx, membrane depolarization, and excitation of sensory nerve fibers of the oronasal cavities in mammals and bitter-sensing cells in insects. We also illustrate how TRP channel expression patterns and functionalities vary between species, leading to intriguing evolutionary adaptations to the specific habitats and life cycles of individual organisms.

Fatty acid composition in native bees: Associations with thermal and feeding ecology

Fatty acid (FA) composition of lipids plays a crucial role in the functioning of lipid-containing structures in organisms and may be affected by the temperature an organism experiences, as well as its diet. We compared FA composition among four bee genera: Andrena, Bombus, Megachile, and Osmia which differ in their thermal ecology and diet. Fatty acid methyl esters (FAME) were prepared by direct transesterification with KOH and analyzed using gas-liquid chromatography with a flame ionization detector. Sixteen total FAs ranging in chain length from eight to 22 carbon atoms were identified. Linear discriminant analysis separated the bees based on their FA composition. Andrena was characterized by relatively high concentrations of polyunsaturated FAs, Bombus by high monounsaturated FAs and Megachilids (Megachile and Osmia) by relatively high amounts of saturated FAs. These differences in FA composition may in part be explained by variation in the diets of these bees. Because tongue (proboscis) length may be used as a proxy for the types of flowers bees may visit for nectar and pollen, we compared FA composition among Bombus that differed in proboscis length (but have similar thermal ecology). A clear separation in FA composition within Bombus with varying proboscis lengths was found using linear discriminant analysis. Further, comparing the relationship between each genus by cluster analysis revealed aggregations by genus that were not completely separated, suggesting potential overlap in dietary acquisition of FAs.

Mammalian phospholipid homeostasis: evidence that membrane curvature elastic stress drives homeoviscous adaptation in vivo

Several theories of phospholipid homeostasis have postulated that cells regulate the molecular composition of their bilayer membranes, such that a common biophysical membrane parameter is under homeostatic control. Two commonly cited theories are the intrinsic curvature hypothesis, which states that cells control membrane curvature elastic stress, and the theory of homeoviscous adaptation, which postulates cells control acyl chain packing order (membrane order). In this paper, we present evidence from data-driven modelling studies that these two theories correlate in vivo. We estimate the curvature elastic stress of mammalian cells to be 4-7 × 10(-12) N, a value high enough to suggest that in mammalian cells the preservation of membrane order arises through a mechanism where membrane curvature elastic stress is controlled. These results emerge from analysing the molecular contribution of individual phospholipids to both membrane order and curvature elastic stress in nearly 500 cellular compositionally diverse lipidomes. Our model suggests that the de novo synthesis of lipids is the dominant mechanism by which cells control curvature elastic stress and hence membrane order in vivo These results also suggest that cells can increase membrane curvature elastic stress disproportionately to membrane order by incorporating polyunsaturated fatty acids into lipids.

Acyl-CoA Dehydrogenase Drives Heat Adaptation by Sequestering Fatty Acids

Cells adapt to temperature shifts by adjusting levels of lipid desaturation and membrane fluidity. This fundamental process occurs in nearly all forms of life, but its mechanism in eukaryotes is unknown. We discovered that the evolutionarily conserved Caenorhabditis elegans gene acdh-11 (acyl-CoA dehydrogenase [ACDH]) facilitates heat adaptation by regulating the lipid desaturase FAT-7. Human ACDH deficiency causes the most common inherited disorders of fatty acid oxidation, with syndromes that are exacerbated by hyperthermia. Heat upregulates acdh-11 expression to decrease fat-7 expression. We solved the high-resolution crystal structure of ACDH-11 and established the molecular basis of its selective and high-affinity binding to C11/C12-chain fatty acids. ACDH-11 sequesters C11/C12-chain fatty acids and prevents these fatty acids from activating nuclear hormone receptors and driving fat-7 expression. Thus, the ACDH-11 pathway drives heat adaptation by linking temperature shifts to regulation of lipid desaturase levels and membrane fluidity via an unprecedented mode of fatty acid signaling.

Thermo-sensitive response based on the membrane fluidity adaptation in Paramecium multimicronucleatum

Relationships between the thermo-sensitive response and membrane lipid fluidity were studied using a ciliated protozoan, Paramecium multimicronucleatum. Paramecium elicits a transient membrane depolarization in response to a cooling stimulus (temperature drop). The depolarization amplitude was largest when the cooling stimulus was started from the culture temperature, whilst when cooling started at a temperature more than 5°C higher or lower than the culture temperature, only a small depolarization was induced. Therefore, the cooling-induced response was dependent on the culture temperature and its sensitivity to the cooling stimulus was highest at the culture temperature. Membrane fluidity measurements of living cells using the fluorescent dye 6-lauroyl-2-dimethylaminonaphthalene (laurdan) showed that the fluidity measured at the culture temperature was almost constant irrespective of the temperature at which the cells had been cultured and adapted, which is consistent with homeoviscous adaptation. The constant fluidity at the culture temperature quickly decreased within a few seconds of application of the cooling stimulus, and the decreased fluidity gradually readapted to a constant level at the decreased temperature within 1 h. When the constant fluidity at culture temperature was modified by the addition of procaine or benzyl alcohol, the cooling-induced depolarization was completely abolished. These results suggest the possibility that the adaptation of fluidity to a constant level and its quick decrease below the constant level activate cooling-sensitive channels to elicit the transient depolarization.

Correlation between thermotolerance and membrane properties in Paramecium aurelia

The relationship between thermotolerance and membrane properties was studied by using a ciliated protozoan, Paramecium aurelia. P. aurelia is a complex of sibling species termed ;syngens' whose cell morphology appear similar on microscopic examination. From the comparison of tolerance to increasing temperature among 14 syngens of P. aurelia, we selected syngens 2 and 3 as low thermotolerant examples, and syngens 8 and 10 as high thermotolerant examples. The membrane resistance of high thermotolerant syngens measured by injection of a constant inward current was greater than that of low thermotolerant syngens. Membrane fluidity measurements of living cells using the fluorescent dye, 6-lauroyl-2-dimethylaminonaphtalene (laurdan) showed that the fluidity at the cultured temperature was decreased in high thermotolerant syngens compared to that of low thermotolerant syngens. However, when the temperature was increased to the killing temperature of each syngens, the fluidity was increased to almost the same level irrespective of syngen. Furthermore, analysis of fatty acids extracted from whole cells showed that the ratios of unsaturated to saturated fatty acids was smaller in high thermotolerant syngens than in low thermotolerant syngens. These results suggest that the thermotolerance of P. aurelia syngens is determined by the membrane fluidity which is related to the fatty acids composition.

Characterization of porcine stable kidney cell line adapted to hyperthermic temperature

The optimum temperature for the growth of porcine stable (PS) kidney cell line is 37 degrees C. We have adapted the cell line to grow at 40 degrees C. The original cell line grown at 37 degrees C has been denoted as PS-37, and the adapted new strain has been denoted as PS-40. Both the cell lines were screened for mycoplasma by Hoechst staining and tritiated uridine-uracil uptake and were found to be negative. Comparative characterization of PS-40 and its progenitor PS-37 cell line was done by using various parameters. The antigenic studies indicated that the new cell strain was not cross-contaminated with any other cell lines. It was observed that PS-40 cells were more fibroblastic with clean cytoplasm and appeared healthy. The growth of PS-40 cells was faster than the original cell line. The karyological study showed heteroploid chromosome number in PS-40 cells. The modal chromosome number of PS-40 cells was 58, whereas that of PS-37 cell line was 38. The lactic dehydrogenase isoenzyme pattern showed a cathodal shift of bands. The PS-40 cell strain could be cryopreserved and revived. The viability of PS-37 as well as PS-40 cell lines is in the range of 90-95%, and the growth characteristics of thawed cells showed six- to eightfold multiplications within 5 d. The virus susceptibility study revealed that the cytopathic effect was more profound and observed 1 d earlier in PS-40 cell line. Increased yields of Japanese encephalitis, Sindbis, and Semliki forest viruses were obtained by 1.8, 1.75, and 1.5 log plaque-forming units/ml, respectively. The yield of West Nile virus was, however, comparable to that in PS-37 cell line. Both the cell lines were refractory to Dengue viruses.

The effect of cold stress on ganglioside fatty acid composition and ganglioside-bound sialic acid content of rat brain subcellular fractions

The effect of cold stress on the ganglioside fatty acid composition and sialic acid content of brain subcellular fractions and homogenate of rats was studied, the animals were kept in a cold room with 12h light-dark cycles at 3 and 10 degrees C for 2 weeks. (1) The rat brain homogenate, synaptosomes and myelin of rats exposed to 3 degrees C contained significantly higher amounts of ganglioside-bound sialic acid per mg of protein than these fractions of control rats kept at 23 degrees C; the differences were less pronounced in rats exposed to 10 degrees C. (2) A small, but significant, diminution of relative palmitic acid content and an increase of stearic acid content was found to take place in gangliosides from rat brain synaptosomes, synaptosomal plasma membranes and homogenate as a result of the exposure of animals to 3 degrees C and to a lesser extent to 10 degrees C. (3) The content of unsaturated fatty acids in gangliosides from brain subcellular fractions was approximately the same in cold exposed and control rats.

Adaptation of an insect cell line of Spodoptera frugiperda to grow at 37 degrees C: characterization of an endodiploid clone

Sf21 and Sf9 cell lines established from the lepidoptera Spodoptera frugiperda do not display major induction of heat shock proteins when exposed to a temperature of 37 degrees C. After some months of adaptation at 37 degrees C we obtained two new cell lines, Sf21-HT and Sf9-HT, which have now been established for several years in our laboratory. The Sf9-HT line displays a slightly shorter doubling time at 37 degrees C than the wild type at 28 degrees C, but cell lethality gives rise to an earlier growth arrest. The composition of total lipid extract from heat-adapted cells reveals a higher sphingomyelin to phosphatidylcholine ratio and a higher percentage of saturated fatty acids, which are expected for the lower membrane fluidity, required for thermotolerance. The cell volume of Sf9-HT is doubled, and by flow cytometry we showed that the DNA content is twice that in the parental cell line. Karyotypic examination of metaphasic cells achieved under epifluorescence microscopy revealed a doubled chromosome number in Sf9-HT.

Cholesterol increases the thermal stability of the Ca2+/Mg(2+)-ATPase of cardiac microsomes

The effect of membrane cholesterol on the thermal inactivation of Ca2+/Mg(2+)-ATPase activity of bovine cardiac microsome was measured and compared to the thermal denaturation profiles of the microsomes as measured by differential scanning calorimetry (DSC). Inactivation, defined as loss of activity, and denaturation, defined as conformational unfolding, were irreversible under the conditions used. Both thermal inactivation of Ca2+/Mg(2+)-ATPase activity and thermal denaturation were shifted to higher temperatures in microsomes enriched with cholesterol (37 +/- 5 micrograms cholesterol/mg protein, cholesterol/phospholipid molar ratio 0.31) compared to control microsomes (15 +/- 3 micrograms cholesterol/mg protein, molar ratio 0.12). Thermal inactivation was measured by two methods: first, measuring activity at room temperature as a function of heating to elevated temperatures at 1 K/min, where inactivation temperatures (T1, temperature of half activity) were 58.9 +/- 0.3 degrees C for control membranes and 59.9 +/- 0.1 degrees C for cholesterol-enriched membranes, respectively. Second, measuring ATPase activity as a function of time at constant temperature, where T1 values of 57.6 +/- 0.5 degrees C and 59.2 +/- 0.5 degrees C were determined for control and cholesterol-enriched membranes, respectively. DSC profiles of microsomal membranes consisting of a number of overlapping peaks were obtained. A well resolved component (transition C) was observed with a transition temperature (T 1/2) of 58.2 degrees C. This T 1/2, which is a measure of conformational stability, correlates with the T1 for Ca2+/Mg(2+)-ATPase activity and is 1.9 +/- 0.6 K higher in cholesterol-enriched membranes. Thus, the increased resistance to inactivation appears to be due to increased conformational stability of the protein induced by cholesterol, demonstrating that a change in lipid composition can influence the stability of an integral membrane protein in a natural membrane. The increased stability is of sufficient magnitude to account for the previously observed correlation between cholesterol content and resistance to heat shock in several cell lines.

Heat stress lipids and schizophrenia

The neurodevelopmental hypothesis of schizophrenia implicates abnormal or disrupted neural growth during embryogenesis. It is postulated here that stress-inducing agents acting upon a compromised cellular system resulting from abnormal plasma membrane lipids could effect the neuronal abnormalities observed in schizophrenia. The heat stress response is induced by exposure to hyperthermia as well as a variety of other agents. The response to these agents includes the cessation of most transcriptional and translational activities, accompanied by the induction of a highly specific set of proteins. A concomitant reduction in metabolic activity including cell cycle delays is also observed. Much of the enormous literature on the heat stress response concentrates on protein and DNA interactions, especially with regard to transcriptional control. However, a variety of lipids are intrinsically involved in the heat stress response. This paper will provide a brief introduction to the heat shock proteins and will explore the roles that lipids play in the heat shock response.

In vivo 19F NMR studies of hyperthermia: hydrophobic environments probed by halothane

The steady-state distribution of the general anesthetic halothane in different rat tissues, including a renal adenocarcinoma with and without hyperthermia treatment, has been evaluated by in vivo 19F NMR spectroscopy. The 19F spectra of halothane (which is a hydrophobic probe) from within tissue show differences in the partitioning between normal rat tissues and adenocarcinoma. Muscle, as a control tissue, exhibits a single large resonance around 0 ppm. However, the adenocarcinoma exhibits two slow-exchanging resonances separated by 0.3 ppm with the one at the more hydrophobic chemical shift being more sensitive to hyperthermia treatment. The results from this tumor model suggest that 19F NMR spectroscopy may be useful first in detecting a change in hydrophobic environments using a lipophilic probe such as halothane, and secondly in monitoring the effects of hyperthermia, a treatment whose effectiveness may involve changes at the level of the plasma membrane. Under conditions of continuous delivery, a resonance which is not detected in the spectra of halothane in excised tissue appears 5 ppm downfield from the resonance for halothane localized in tissues. A rotating frame experiment is used to show that this resonance is derived from anesthetic absorbed on the tissue surface.

Effect of dietary modulation of membrane lipid composition on the thermostability of HTC cells and of a membrane enzyme

Growth of hepatoma tissue culture (HTC) cells in the presence of linoleic (18:2) or arachidonic (20:4) acids for 36 h caused an increased cell thermosensitivity. Plasma membrane-rich fractions were purified (15-20-fold) with high yield (30%) from control and fatty acid-supplemented cells. Contamination with membranes from mitochondria, lysosomes and endoplasmic reticulum was low. Supplementation significantly increased the level of the supplemented fatty acid and decreased the level of oleic acid (18:1) in plasma membrane phospholipids (PL), causing a significant decrease in the oleic acid:PUFA (polyunsaturated fatty acid) ratio. No significant changes occurred in other parameters such as cholesterol:PL, cholesterol:protein or PL:protein ratios. Plasma membranes from PUFA-supplemented cells exhibited a lower membrane order, compared with control cell membranes, as determined by DPH fluorescence polarization over the temperature range 4-40 degrees C. Isothermal inactivation of alkaline phosphodiesterase I in plasma membranes from control and supplemented cells showed curvilinear kinetics. The change in membrane composition and order following supplementation with arachidonic acid was associated with increased thermosensitivity of this enzyme. These data are discussed with respect to the suggestion that the plasma membrane may be a target for cellular thermal injury and death.

Acyl-CoA: cholesterol acyltransferase and 3-hydroxy-3-methylglutaryl-CoA reductase in carp-liver microsomes: effect of cold acclimation on enzyme activities and on hepatic and plasma lipid composition

Hepatic microsomal activities of acyl-CoA:cholesterol acyltransferase (ACAT) and 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase, rate-limiting enzymes in cholesterol esterification and cholesterol synthesis, and the concentration sand compartmentalization of esterified and unesterified cholesterol, were studied in carp acclimated to 10 and 30 degrees C. Irrespective of acclimation temperature, carp-liver ACAT is characterized by an apparent Km-value for oleoyl-CoA of 11-15 microM and displays an optimum activity at pH 7.4. The enzyme activity is reduced approx. 2-fold upon preincubation of microsomes with alkaline phosphatase. Arrhenius plots of ACAT-activity are curvilinear, with curvatures considerably affected by the acclimation temperature of the fish. Carp HMG-CoA reductase has been characterized previously by Teichert and Wodtke ((1987) Biochim. Biophys. Acta 920, 161-170). When measured at 30 degrees C, ACAT activities from 30 degrees C- and 10 degrees C-acclimated carp are identical (approx. 6 pmol/min per mg protein), whilst 'expressed' HMG-CoA reductase activity (18.1 +/- 12.2 pmol/min per mg protein for 30 degrees C-acclimated carp vs. 159.8 +/- 106.6 pmol/min per mg protein for 10 degrees C-acclimated carp) is enhanced 9-fold in the cold environment. This disparity indicates that cold-acclimation results in a massive increase in the capacity for hepatic cholesterol synthesis relative to hepatic cholesterol esterification. At the same time, hepatic compositional analysis reveals identical contents of unesterified cholesterol in either groups of carp but significantly decreased (3-fold) amounts in cholesterol ester (and also in triacylglycerol, 4-fold) in cold-acclimated carp. Moreover, microsomal fractions display lower cholesterol to phospholipid ratios in the cold. In contrast, concentrations of either cholesterol fractions (and of triacylglycerols) in plasma--the mobile compartment for lipoprotein transport--do not differ in cold- and warm-acclimated carp. Based on current concepts of cholesterol metabolism, it is concluded that the cold-enhanced expression of hepatic HMG-CoA reductase activity is a homeostatic response directed against and compensating for a cold-induced but not yet characterized deficiency in hepatic cholesterol availability.

Cultured human skin fibroblasts modify their plasma membrane lipid composition and fluidity according to growth temperature suggesting homeoviscous adaptation at hypothermic (30 degrees C) but not at hyperthermic (40 degrees C) temperatures

Mammalian cell metabolism is responding to changes in temperature. Body temperature is regulated around 37 degrees C, but temperatures of exposed skin areas may vary between 20 degrees C and 40 degrees C for extended periods of time without apparent disturbance of adequate cellular functions. Cellular membrane functions are depending from temperatures but also from their lipid environment, which is a major component of membrane fluidity. Temperature-induced changes of membrane fluidity may be counterbalanced by adaptive modification of membrane lipids. Temperature-dependent changes of whole cell- and of purified membrane lipids and possible homeoviscous adaptation of membrane fluidity have been studied in human skin fibroblasts cultured at 30 degrees C, 37 degrees C, and 40 degrees C for ten days. Membrane anisotropy was measured by polarized fluorescence spectroscopy using TMA-DPH for superficial and DPH for deeper membrane layers. Human fibroblasts were able to adapt themselves to hypothermic temperatures (30 degrees C) by modifying the fluidity of the deeper apolar regions of the plasma membranes as reported by changes of fluorescence anisotropy due to appropriate changes of their plasma membrane lipid composition. This could not be shown for the whole cells. At 40 degrees C growth temperature, adaptive changes of the membrane lipid composition, except for some changes in fatty acid compositions, were not seen. Independent from the changes of the membrane lipid composition, the fluorescence anisotropy of the more superficial membrane layers (TMA-DPH) increased in cells growing at 30 degrees C and decreased in cells growing at 40 degrees C.

Content and composition of hopanoids in Zymomonas mobilis under various growth conditions

By using a new method for quantification of the different hopanoid derivatives, a total hopanoid content of about 30 mg/g (dry cell weight) was observed in Zymomonas mobilis. This value is the highest reported for bacteria so far. The major hopanoids in Z. mobilis were the ether and glycosidic derivatives of tetrahydroxy-bacteriohopane, constituting about 41 and 49% of the total hopanoids. Tetrahydroxybacteriohopane itself, diplopterol, and hopene made up about 6, 3, and 1%, respectively. Only minor changes in hopanoid composition were observed with changes in growth conditions. Earlier reports on a correlation between hopanoid content and ethanol concentration in the medium could not be confirmed. Over a wide range of ethanol concentrations (5 to 60 g/liter), growth rates (0.08 to 0.25 h-1), and temperatures (25 to 37 degrees C), the molar ratio of hopanoids to phospholipids in the cells amounted to about 0.7. Only at growth rates of greater than 0.30 h-1 did the molar ratio increase to about 1.

The effect of the administration of ethanol to rats on the thermal sensitivity of transplantable tumours

1. Long-term maintenance of rats on a diet containing ethanol did not cause compensatory changes in brain synaptic membrane lipid composition, nor was there any change in membrane lipid order as measured by steady-state fluorescence polarization of DPH. 2. The lipid composition of MC7 tumour plasma membranes was also determined in ethanol-fed and then sucrose pair-fed controls. Dietary ethanol caused no change in the composition of phospholipid classes. There was, however, a tendency for an increase in C18 fatty acids and an increase in monounsaturated at the expense of unsaturated and polyunsaturated fatty acids. There was no significant change in cholesterol content. 3. Tumour membranes from ethanol-fed rats were not different in lipid order from their pair-fed controls. Tumour membranes were, however, significantly less ordered than synaptic membranes. 4. A single heat treatment of 44 degrees C for 1 h increased the survival time of rats bearing both MC7 and D23 foot tumours. No difference in their survival was seen between ethanol-fed and sucrose pair-fed controls.

Incorporation of [3H]acetate into the membrane lipids of a murine tumour during the development of thermotolerance

The incorporation of [3H]acetate into the membrane lipids of a C3H mammary adenocarcinoma, grown s.c. in the hind paw of CBA mice, was followed to estimate the effects on the de novo synthesis of membrane lipids after hyperthermic treatments. Thermotolerance developed in response to a heat treatment at 43 degrees C for 20 min, as verified through growth rate studies of tumours exposed to fractionated heat treatments. Our results show that, during the development of thermotolerance, the relative rates of incorporation of [3H]acetate into the major lipid classes of the tumour cell membranes change significantly. The de novo synthesis of phospholipids decreased while that of cholesteryl esters plus triglycerides increased. The incorporation of [3H]acetate into cholesterol remained constant. Consequently, the ratio [3H]cholesterol/[3H]lecithin increased significantly during the development of thermotolerance. When the incorporation of [3H]acetate was followed 72-96 h after the heat treatment, i.e. at the interval at which heat resistance was observed to approach that of control tumours, the incorporation into cholesterol was significantly reduced while incorporation into phospholipids increased to control levels. Thus, the ratio [3H]cholesterol/[3H]lecithin was significantly lower, when compared to that of control tumours. The functional relationship between the heat-induced changes in the de novo synthesis of membrane lipids and the development of thermotolerance is discussed with regard to a mechanism based on homeoviscous adaptation of the membranes.

Membrane lipids of B16 melanoma cells and heat-resistant variants

Membrane lipid composition and fluidity of a series of B16 melanoma cell variants with increased resistance to heat were analysed for changes within the lipid component that may contribute to the acquisition of heat resistance. Within one series of heat-resistant lines the cholesterol content of the cells decreased as their heat resistance increased. The most heat-resistant line, WH75, had 40 per cent less cholesterol than the parent line. No change in the composition of phospholipid fatty acids was found. An increased level of membrane fluidity in WH75 was demonstrated by electron paramagnetic resonance using 5- or 12-doxyl stearic acid. When challenged by heat the increase in membrane fluidity was similar for WH75 and for the parent line. Thus the increased heat resistance of the variants is probably not due to their ability to adapt to heat challenge by increasing membrane thermostability. The inverse relationship between heat resistance and cholesterol content was not demonstrated in two other series of heat-resistant variants. The cholesterol decrease, therefore, is not a universal response of cells as they acquire heat resistance.

Distribution of 5-doxylstearic acid in the membranes of mammalian cells

Concentration-dependent spin broadening of ESR spectra of the nitroxide 5-doxylstearic acid has been used to evaluate the distribution of 5-doxylstearic acid in the membranes of intact mouse thymus-bone marrow (TB) and Chinese hamster ovary (CHO) cells. TB cells, CHO cells, erythrocytes, and isolated plasma membranes from CHO cells were labelled with 5-doxylstearic acid and the peak to peak linewidths of the central line of the resulting ESR spectra were measured. The measured line widths were linearly dependent on the amount of 5-doxylstearic acid incorporated into the sample over the range of 0-0.18 mol nitroxide per mol lipid. In erythrocytes, the relationship between linewidths approximated a linear function at lower concentrations of 5-doxylstearic acid, up to 0.07 mol nitroxide per mol lipid. The amount of broadening of the central line for a given amount of 5-doxylstearic acid was far less for intact cells than for either erythrocytes or plasma membrane, indicating that the 5-doxylstearic acid samples a much larger lipid pool in the intact cells. With the broad assumption that the mobility of the 5-doxylstearic acid is similar in different membranes, the size of the lipid pool sampled by 5-doxylstearic acid is approximately equal to the total cellular lipid in intact cells. If a given concentration of 5-doxylstearic acid sampled only the plasma membrane of TB or CHO cells, we would expect to see a linewidth corresponding to a 12-20-fold greater local concentration of 5-doxylstearic acid than was observed, since the plasma membranes of CHO and TB cells represent only 5-8 percent of the total cellular lipid. Therefore, the 5-doxylstearic acid must distribute into most or all cellular membranes of intact cells and is not localized in the plasma membrane alone.

Thermal adaptation and heat shock response of Tilapia ovary cells

The growth of tissue culture TO-2 cells derived from the warm water fish Tilapia, the induction of thermotolerance, and protein synthesis profiles of these cells in response to temperature changes were examined. TO-2 cells can grow between 15 to 34 degrees, with an optimal growth temperature of 31 degrees. There is no apparent killing of the cells when the temperature is lowered to 4 degrees for up to 3 days. Survival of TO-2 cells at 43 degrees was studied after various preheat treatments: 1) acute heating at 40 degrees for 15 min followed by 31 degrees incubation, 2) chronic exposure at 37 degrees for several hr, or 3) long-term thermal adaptation at 34 degrees. The cells acquire thermotolerance from pre-exposure to 37 degrees for as short as 6 hr. Preheating at 40 degrees followed by incubation at 31 degrees also induces thermotolerance against a subsequent 43 degrees heat challenge. In addition, 34 degrees thermal adapted cells are resistant to 43 degrees heating. One- and two-dimensional gel electrophoresis of proteins after heat treatments show that three major heat shock proteins with molecular weights around 87, 70, and 27 kD are preferentially synthesized. The synthesis of two additional proteins with an isoelectric point of 6.9 and molecular weights of 60 and 44 kD are significantly enhanced in 34 degrees thermal-adapted and 37 degrees chronic heated cells, but not in cells subjected to an acute heat shock at either 40 degrees or 43 degrees. On the other hand, the 27 kD heat shock proteins are mainly present in the 43 degrees, 40 degrees, and 37 degrees heat-shocked cells, but not in the 34 degrees thermal-adapted cells.

Lipid composition and temperature adaptation of the nervous system of the leech Hirudo medicinalis L

The lipid composition of the nervous system of the leech Hirudo medicinalis was investigated following acclimatization of animals at 25 degrees C and 5 degrees C. Choline, ethanolamine, and serine plus inositol phosphoglycerides are the major phospholipid classes of the leech ganglionic chain; minor amounts of lysophosphatidylcholine, phosphatidic acid, and sphingomyelin are also present. Neither the phospholipid pattern nor the cholesterol to total phospholipid molar ratio was dependent on the acclimatization temperature, whereas the fatty acid patterns of choline and serine plus inositol phosphoglycerides were significantly affected. Both for choline and serine plus inositol phosphoglycerides, a significant increase of the unsaturation index and a decrease of saturated to unsaturated fatty acid ratio was observed in animals acclimatized at 5 degrees C in comparison with those acclimatized at 25 degrees C. These observations, which point to increased lipid fluidity of the nervous system of cold-adapted leeches, are strengthened by results obtained by the fluorescence polarization method using 1,6-diphenyl-1,3,5-hexatriene as a probe: a decrease of the fluorescence polarization value was observed throughout the temperature range selected (5-40 degrees C).

Heat stress stimulates inositol trisphosphate release and phosphorylation of phosphoinositides in CHO and Balb C 3T3 cells

Exposure of eukaryotic cells to elevated temperature leads to profound switches in cell metabolism and gene expression which may be involved in cellular homeostatic mechanisms. We have investigated the effect of heat shock (45 degrees C) on the metabolism of the phosphoinositides, a class of phospholipids involved in the function of Ca2+ -linked membrane receptors. Heat shock led to stimulation of phosphoinositide turnover in HA1-CHO and Balb C 3T3 cells, resulting in the rapid accumulation of inositol trisphosphate (IP3). Mitogenic and alpha 1 adrenergic stimulation, with serum or phenylephrine, led to similar increases in IP3. Heat shock also caused rapid increase in phosphorylation of polyphosphoinositides (PPI). Prolonged exposure to heat greater than 15 min at 45 degrees C led to progressive cellular toxicity which was associated with depletion of PPI. This decline in PPI concentration appeared to result from inhibition of PPI resynthesis. In this respect, heat may resemble some other types of cellular stresses in stimulating membrane phospholipases to deplete classes of membrane phospholipids. The induction of PPI turnover may, therefore, be involved in both pleiotropic responses to brief heat shock and toxicity resulting from prolonged thermal stress.

Combined electron-spin-resonance, X-ray-diffraction studies on phospholipid vesicles obtained from cold-hardened wheats : II. The role of free sterols

The contents of free sterols and phospholipids in leaves of wheat, Triticum aestivum L., cultivars of different frost resistances, as well as the physical state of isolated phospholipids in the presence and absence of sterols, were compared before and after hardening. There was an inverse relationship between the sterol/phospholipid ratio and frost tolerance as a consequence of both a decrease in the free sterol, and an increase in the total phospholipid content. Sterol-sterol interactions were investigated using wide angle X-ray diffraction, while the phase behaviour of phospholipid vesicles was studied using the electron-spin-resonance (ESR) technique. No sterol-sterol interactions at-10° C were detected in vesicles obtained from the hardened most cold-tolerant cultivar (Miranovskaja 808), containing sterols in a ratio (0.08) found in the original lipid extracts. In contrast, when the sterol-phospholipid ratio in the vesicles was set to the level (0.39) found in the extracts of the most sensitive cultivar, Penjamo 62, the appearance of sharp reflexion rings at 4.5·10(-1), 4.8·10(-1) and 5.0·10(-1) nm indicated strong sterol-sterol interactions. The temperatures for the onset of phase separation for vesicles of identical sterol/phospholipid ratios found in lipid extracts of hardened Miranovskaja 808 were almost the same as those measured in purified phospholipids (-15 vs.-16° C). In contrast, the temperature for the onset of phase separation of vesicles with a sterol/phospholipid ratio characteristic of hardened Penjamo 62 was shifted upwards (from-6 to-2° C). Phase separation was not completed in the vesicles of Miranovskaja 808 in the temperature range scanned (-30° C) but was shifted from-22 to-18° C in the presence of sterols in the case of Penjamo 62. The results are discussed in terms of the composition and physical state of membranes in relation to survival at freezing temperatures.

Membrane effects of ionizing radiation and hyperthermia

Results of numerous studies demonstrate that membranes are important sites of cell damage by both ionizing radiation and hyperthermia. Modification of membrane properties (mainly lipid fluidity) affects the cellular responses to radiation and hyperthermia but former concepts that membrane rigidification sensitizes cells to radiation while membrane fluidization potentiates hyperthermic damage have now been seriously challenged. It seems that the effects of membrane fluidity on cell responses to hyperthermia and radiation are due to an indirect influence on functional membrane proteins. The major role of lipid peroxidation in radiation damage to membranes has also been questioned. The existing evidence makes it unlikely that the interaction between radiation and hyperthermia is determined by the action of both agents on the same membrane components.

Hydrogen peroxide toxicity may be enhanced by heat shock gene induction in Drosophila

Recent evidence suggests that low dose exposure of cells to hydrogen peroxide and/or induction of heat shock protein (HSP) synthesis will render cells resistant to the lethal effects of a subsequent high dose hydrogen peroxide stress. We explored this possibility in the Drosophila melanogaster Schneider tissue culture line 2. It was found that chronic low dose exposure (1 mM H2O2 for 3 days) resulted in marked potentiation of the toxic effects of a subsequent high dose exposure (50 mM H2O2 for 1 h), as assessed by impairment of uridine incorporation and cell proliferation. Cells preexposed to low dose H2O2 exhibited enhanced heat shock gene transcription upon exposure to high dose H2O2, as compared to cells that did not receive low dose preexposure. Transcriptional induction of the heat shock genes by a mild non-toxic heat shock resulted in marked enhancement of the anti-proliferative effects of a subsequent H2O2 exposure. Thus, low dose hydrogen peroxide exposure or mild heating results in subsequent enhancement of high dose hydrogen peroxide toxicity; this effect correlates with enhanced heat shock gene expression. Possible mechanisms are discussed.

The effect of hyperthermia on glucose transport in normal and thermal-tolerant Chinese hamster ovary cells

The effect of hyperthermia on glucose transport was studied in CHO cells to test the hypothesis that interference with membrane transport might be related to cell death at elevated temperatures. It was shown that passive diffusion of 2-deoxyglucose increases steadily over the temperature range 4-50 degrees C. Facilitated diffusion increases from 4 degrees C to 35 degrees C then exhibits a broad optimum before decreasing rapidly above 45 degrees C. The temperature dependence of glucose transport in thermally resistant cells was not however different from that of normal cells suggesting that this membrane transport process is not a critical target in cell killing by heat.

Cholesterol content and heat sensitivity of nine mammalian cell lines

The cholesterol, phospholipid and protein contents of nine mammalian cell lines, three lymphoid and six attached cell lines, were measured, along with the sensitivity of the cells to hyperthermia at 42 degrees and 44 degrees C. The free cholesterol content and the protein content per cell correlated positively with the time required to kill 99 per cent of the cells at 44 degrees C. The phospholipid content showed a less significant positive correlation whilst the cholesterol ester content and the cholesterol:phospholipid molar ratio did not correlate with heat sensitivity. There were no correlations observed when the levels of these cell components were compared to heat survival at 42 degrees C. As the three lymphoid lines are small, very heat sensitive cells, the six monolayer lines were analysed separately. In this case, only the protein and the free cholesterol content maintained a significant correlation (at the 5 per cent level). It is concluded that the levels of cholesterol or phospholipid cannot be used as reliable indicators of the heat sensitivity of a cell.

Variations in dietary triacylglycerol saturation alter the lipid composition and fluidity of rat intestinal plasma membranes

Rats were maintained on nutritionally complete diets enriched in unsaturated (corn oil) or saturated (butter fat) triacylglycerols. After 6 weeks, significant differences in the lipid composition and fluidity of a number of intestinal membranes were observed. The corn oil diet (enriched mainly in linoleic acid) increased the overall unsaturation of the acyl chains and enhanced the lipid fluidity, as assessed by the fluorescence anisotropy of 1,6-diphenyl-1,3,5-hexatriene, of enterocyte microvillus and basolateral membranes and of colonocyte basolateral membranes. Concomitantly, the cholesterol content and the cholesterol/phospholipid molar ratio were increased in the microvillus but not in the basolateral membranes. The increased cholesterol in ileal microvillus membranes can result from enhanced cellular biosynthesis, since ileal slices from rats fed the unsaturated diet incorporated [14C]octanoate more rapidly into digitonin-precipitable sterol. Increased fluidity of the enterocyte microvillus and basolateral membranes, respectively, enhanced the enzyme specific activities of p-nitrophenylphosphatase and (Na+ + K+)-dependent adenosine triphosphatase. The results indicate that the lipid composition, fluidity and enzyme activities of intestinal plasma membranes can be altered by dietary means. Moreover, rat enterocytes possess regulatory mechanisms which modulate the cholesterol content of the microvillus membranes so as to mitigate changes in lipid fluidity.

Hyperthermia, Na+K+ATPase and lactic acid production in some human tumour cells

When HeLa cells are exposed to brief heat shock at 45 degrees C there is a reduction in the cellular level of Na+K+ATPase. Return of the cells to the normal growth temperature of 37 degrees C leads to a partial restoration of enzyme activity. The pattern of this recovery of activity suggests that it may be associated with the induction of heat shock proteins. Indeed other means of heat shock protein induction such as continuous heat treatment at 42 degrees C, or treatment of cells at 37 degrees C with sodium arsenite, leads to elevated levels of Na+K+ATPase activity and alterations in the kinetic properties of the enzyme. Continuous hyperthermia at 42 degrees C led to increased lactate production which could be blocked with ouabain suggesting that effects on Na+K+ATPase activity could partly influence glycolysis. A number of other human and hamster cells also showed increased lactate production at 42 degrees C and also an inhibition of lactate production by ouabain. Whilst incubation of HeLa cells with cyanide had little effect on glycolysis at 37 degrees C elevation of the temperature to 42 degrees C (or 45 degrees C), in the presence of cyanide, impaired glycolysis. The possible role in this phenomenon, of an unusual oxygen-sensitive isoenzyme of lactate dehydrogenase, expressed in human cancers, is discussed.

Stable heat-resistant clones selected from wild-type and surface variants of B-16 melanoma

Stable heat-resistant clones were selected from wild-type B-16 melanoma cells and from three of their surface variants resistant to the lectins wheat-germ agglutinin, ricin and concanavalin A. The selection procedure included three or four cycles of heating the cells in culture at 43 degrees C for 2-1/2 to 3-1/2 h interspersed with growth at 37 degrees C. The survivability of the heat-resistant (HR) variant cells at elevated temperatures of 43 degrees C for 160 min and 45 degrees C for 40 min was 2-4 logs greater than that of their respective parents. This acquired property of heat resistance appeared to be a stable phenomenon, persisting in these cell lines for more than 80 generations. One HR variant cell line carried in tissue culture for 250 generations showed no change in the heat-resistance characteristic. Acquisition of resistance appeared to be a gradual process with intermediate stages preceding the more pronounced degree of resistance. These newly selected HR variants join the existing surface variants of B-16 melanoma to result in a large family of variants from the same cell lineage to make this system a powerful tool for studying the relationship between heat sensitivity, metastasis and hyperthermia treatment of cancer.

Thermal sensitivity and resistance of insulin-receptor binding in thermotolerant cells

Cells may be made extremely resistant to elevated temperatures (thermotolerant) by a mild heat shock a few hours prior to more rigorous heating. In the present report, we show that a single cellular process - insulin binding to its receptor (in HA-1 Chinese hamster ovary cells) - may be made similarly heat-resistant. Heat resistance, whether expressed as cell survival or insulin binding, had similar dose-response characteristics, showing maximum resistance after 30 min at 43 degrees C. The processes had similar induction kinetics (2-6 h) and decayed over a similar time-course (100 h) after 43 degrees C, 30 min preheating. Thermal resistance of insulin binding was induced only when residual receptor loss (due to heating) occurred. Also, decay of resistance was closely correlated with recovery of insulin binding capacity. There thus appeared to be an inverse relationship between receptor number and the degree of heat resistance of both receptors and whole cells. (Scatchard analysis indicated that decreased insulin binding was due to receptor loss, not affinity decrease.) Whether the insulin receptor has a direct role in the mediation of cell killing or whether it passively reflects the state of the whole cell is not clear. However, identification of the receptor as an entity specifically protected in the thermotolerant cells may permit examination of the expression of thermotolerance at the molecular level.

The effects of membrane modification and hyperthermia on the survival of P-388 and V-79 cells

Cells with greater membrane microviscosities are reportedly less sensitive to being killed by mild hyperthermia. To further study this phenomenon, membrane microviscosity of ascites P-388 tumor cells was increased by adding cholesteryl hemisuccinate (CHS). Unexpectedly, when modified cells were heated for 60 min at 43 degrees C in vitro and analyzed in vivo in CDF1 mice they showed an increased thermal sensitivity. Similar increases in cell membrane microviscosity were obtained with V-79 cells. However, after heat treatment no differences in survival in vitro were noted between modified and unmodified cells. Treatment with CHS alone results in a substantial increase in P-388 cells, which take up trypan blue, but not in V-79 cells. When these 'dead' cells are accounted for, the difference in killing between control and CHS-modified P-388 cells is no longer seen. When considered in this light, both P-388 and V-79 cells are similar in their response to heat, which is not influenced by CHS per se.

Effect of membrane fatty acid changes on the radiation sensitivity of human lymphoid cells

To test the influence of changes in membrane fatty acid composition on the radiation response of mammalian cells, human LDV cells were cultured in medium containing delipidated serum supplemented with either oleic or linoleic acid. Analysis of lipid extracts of the cells by gas liquid chromatography showed that, after 3 or more days growth in oleic or linoleic acid supplemented media, there were substantial overall increases in the proportion of oleate and linoleate, respectively, in the cellular lipid. Smaller absolute changes were measured in nuclear phospholipid, which was found to be low in unsaturated phospholipid compared to the rest of the cell. Fluorescence polarization measurements using diphenylhexatriene indicated an increased membrane fluidity in cells grown in the presence of excess linoleic acid and to a lesser extent for oleic acid. The clonogenic capacity of the cells after irradiation in air or nitrogen was not altered by any of these membrane compositional changes. The lack of effect on radiation sensitivity, in contrast to that reported for bacteria (E. coli K1060), is consistent with the fact that little or no change was brought about in the nuclear membrane composition, since evidence from partial cell irradiation experiments indicates that the cell nucleus is the sensitive target for cell killing by ionizing radiation. The ability of the cell to maintain a low level of unsaturated phospholipids in its nuclear membrane may be an important general defence mechanism against free radical damage to chromatin mediated by lipid peroxidation.

The effects of altered levels of phosphatidylcholine and phosphatidylethanolamine on fatty acid desaturase activity and sterol metabolism during temperature acclimation in a choline auxotroph of Neurospora crassa

Experiments were conducted to determine the effects of choline deprivation on levels of phospholipid fatty acids in a choline auxotroph (chol-1; chol-2) of Neurospora crassa with respect to high (37 degrees C) and low (15 degrees C) growth temperatures and during acclimation following a shift from high to low temperature conditions. Although grossly altered levels of phosphatidylethanolamine and phosphatidylcholine were observed at both temperatures, phospholipid fatty acid levels remained virtually identical to those found in a phenotypically wild-type and maximally supplemented chol-1; chol-2 strains grown under the same conditions. Deprivation of choline from supplemented cultures of the mutant followed by a shift from high to low growth temperatures did not significantly affect the level of fatty acid desaturation with respect to control cultures. Free sterols did not significantly affect the level of fatty acid desaturation with respect to control cultures. Free sterols were reduced, however, and sterol ester levels were elevated in choline-deprived cultures, suggesting that sterol interconversions may be closely tied to aspects of phospholipid biosynthesis. These experiments suggest that although major modifications in membrane fluidity may be brought about by thermally induced changes in fatty acid desaturase activity, it seems probable that additional cellular mechanisms may be involved if fluidity is under precise control.

The effects of temperature acclimation on membrane sterols and phospholipids of Neurospora crassa

Experiments were conducted to examine the effects of temperature acclimation on sterol and phospholipid biosynthesis in Neurospora crassa. Cultures grown at high (37 degrees C) and low (15 degrees C) temperatures show significant differences in free and total sterol content, sterol/phospholipid ratios and distribution of major phospholipid species in total lipids and two functionally distinct membrane fractions. The ratio of free sterols to phospholipids in total cellular lipids from 15 degrees C cultures was found to be about one-half that found at 37 degrees C, whereas sterol/phospholipid ratios of mitochondrial and microsomal membranes were found to be higher at the low growth temperature. Total sterol and phospholipid biosynthetic rates showed parallel reductions in cultures acclimating to a shift from 37 to 15 degrees C growth conditions. Distribution of [14C]acetate label into free sterols was significantly lower under these conditions, however; indicating an increase in the conversion rate of sterols to sterol esters at the lower temperature. Mitochondrial and microsomal membrane fractions showed distinct phospholipid distributions which also differed from total lipid distributions at the two growth temperatures. In each case there was a consistent decrease in phosphatidylcholine and a corresponding increase in phosphatidylethanolamine as growth temperatures were lowered.