Normal Physiological Temperature Research Articles

On-demand drug delivery from temperature-responsive polyurethane membrane

To provide on-demand therapeutics to diseased site where local and intermittent drug delivery was desirable, temperature-responsive polyurethane (TRPU) which enabled rapid, reproducible and tunable on–off switching release of incorporated drugs was successfully prepared. Differential scanning calorimetric analysis revealed that the TRPU synthesized in this study exhibited segmented structure with partially-miscible fixed phase and reversible phase, which favorably imparted the TRPU a physiologically-tolerable switching temperature at 44 °C. Positron annihilation lifetime spectroscopy demonstrated that, as the TRPU underwent sharp phase transition upon heating through 44 °C, the free volume size and fraction within the polymeric matrix expanded dramatically. Based on such discontinuous free volume change, the diffusion of incorporated antibiotic (sulfamethoxazole) and anticancer drug (paclitaxel) from TRPU membrane could be switched off below normal physiological temperature (37 °C) while switched on by heating to 44 °C, resulting in high on–off ratios. In addition, the TRPU membrane could be thermally-switched on and off rapidly, within less than 5 min after temperature variation, and reproducibly, over four cycles of temperature oscillation between 37 °C and 44 °C. Furthermore, the amount of drug released during each on state was found to be proportional to the duration of heating. In cell culture assays, the TRPU membrane exhibited no cytotoxicity towards C2C12 myoblasts, 3T3 fibroblasts, Me-T mesothelials and J.1774 macrophages. Compared with ordinary biomedical polyurethane elastomer that delivered drugs at almost constant rate regardless of temperature variation, the TRPU prepared in this study showed great potential for developing biomedical implant which could provide temperature-modulated therapeutics to diseased site.

Chemical modification of recombinant human keratinocyte growth factor 2 with polyethylene glycol improves biostability and reduces animal immunogenicity

Recombinant human keratinocyte growth factor 2 (rhKGF-2) is a member of fibroblast growth factor protein family currently being investigated for its promising significant effects in treating epithelial damage. Molecular modification with polyethylene glycol (PEGylation) is an effective approach to improve protein biostability and decrease protein immunogenic activity. In this study, we modified rhKGF-2 through PEGylation at N-terminal residue using 20 kDa PEG-phenyl-isothiocyanate (PIT-PEG20K). PEGylated rhKGF-2 is then purified to near homogeneity by Sephadex G-25 gel filtration followed by a Heparin Sepharose TM CL-6B affinity chromatography. This PEGylated rhKGF-2 retained about 60% of mitogenic activity compared to the non-modified rhKGF-2. Its relative thermal stability at normal physiological temperature and structural stability were significantly enhanced. Moreover, the immunogenicity of PEGylated rhKGF-2 in mice is significant decreased compared to non-modified rhKGF-2. These results suggest that PEGylation of rhKGF-2 could be a more effective approach to the pharmacological and therapeutic application of rhKGF-2.

Ultrasound-enhanced drug delivery through sclera.

Achieving an increase in drug delivery through the sclera is important in the treatment of the back of the eye diseases including macular degeneration, diabetic retinopathy, etc. Our objective is to utilize therapeutic ultrasound in enhancing drug delivery through the sclera. Porcine sclera was placed in a standard diffusion cell at a normal physiological temperature of 34 °C. Solution of sodium fluorescein, a hydrophilic drug-mimicking compound, was added to donor compartment, and receiver compartment was filled with saline. The sclera was exposed to ultrasound for 5 min (intensities 1.2–1.8 W/cm2 and frequencies 0.5 to 5 MHz). After 60 min, solution samples were taken from the receiver compartment to determine the concentration of sodium fluorescein. The sclera permeability to the drug mimicking agent in vitro increased 3.5 times at 0.5 MHz (p-value of less than 0.05), 1.7 times at 1 MHz, 3.5 times at 3.5 MHz (p-value of less than 0.05), and 1.5 times at 5 MHz. The average temperature of the sclera during ultrasound exposure was 42 °C. No gross changes were observed in the sclera due to ultrasound application. Future work will focus on determination of optimal ultrasound parameters for the drug delivery through the sclera.

Normothermic Perfusion: A Mini-Review

The quality of organ preservation is critical to the outcome of transplantation: preservation technology is a limiting factor in the further development in the use of marginal donor organs. Normothermic preservation (preservation at normal physiological temperature) enables prolonged preservation, resuscitation after warm ischemia and organ viability assessment before transplantation.

Effect of plasmodial RESA protein on deformability of human red blood cells harboring Plasmodium falciparum

During intraerythrocytic development, Plasmodium falciparum exports proteins that interact with the host cell plasma membrane and subplasma membrane-associated spectrin network. Parasite-exported proteins modify mechanical properties of host RBCs, resulting in altered cell circulation. In this work, optical tweezers experiments of cell mechanical properties at normal physiological and febrile temperatures are coupled, for the first time, with targeted gene disruption techniques to measure the effect of a single parasite-exported protein on host RBC deformability. We investigate Pf155/Ring-infected erythrocyte surface antigen (RESA), a parasite protein transported to the host spectrin network, on deformability of ring-stage parasite-harboring human RBCs. Using a set of parental, gene-disrupted, and revertant isogenic clones, we found that RESA plays a major role in reducing deformability of host cells at the early ring stage of parasite development, but not at more advanced stage. We also show that the effect of RESA on deformability is more pronounced at febrile temperature, which ring-stage parasite-harboring RBCs can be exposed to during a malaria attack, than at normal body temperature.

Change in contractile properties of human muscle in relationship to the loss of power and slowing of relaxation seen with fatigue.

Slow relaxation from an isometric contraction is characteristic of acutely fatigued muscle and is associated with a decrease in the maximum velocity of unloaded shortening (V(max)) and both these phenomena might be due to a decreased rate of cross bridge detachment. We have compared the change in relaxation rate with that of various parameters of the force-velocity relationship over the course of an ischaemic series of fatiguing contractions and subsequent recovery using the human adductor pollicis muscle working in vivo at approximately 37 degrees C in nine healthy young subjects. Maximal isometric force (F(0)) decreased from 91.0 +/- 1.9 to 58.3 +/- 3.5 N (mean +/- s.e.m.). Maximum power decreased from 53.6 +/- 4.0 to 17.7 +/- 1.2 (arbitrary units) while relaxation rate declined from -10.3 +/- 0.38 to -2.56 +/- 0.29 s(-1). V(max) showed a smaller relative change from 673 +/- 20 to 560 +/- 46 deg s(-1) and with a time course that differed markedly from that of slowing of relaxation, showing very little change until late in the series of contractions. Curvature of the force-velocity relationship increased (a/F(0) decreasing from 0.22 +/- 0.02 to 0.11 +/- 0.02) with fatigue and with a time course that was similar to that of the loss of power and the slowing of relaxation. It is concluded that for human muscle working at a normal physiological temperature the change in curvature of the force-velocity relationship with fatigue is a major cause of loss of power and may share a common underlying mechanism with the slowing of relaxation from an isometric contraction.

Thermal dose and the probability of adverse effects from biomedical ultrasound

Absorption of biomedical ultrasound heats tissue. Moderate heating to a few degrees above normal physiological temperatures can perturb biological systems, e.g., by altering normal metabolic processes, while brief, intense heating can kill cells, tissues, or entire organisms. Of particular concern for diagnostic ultrasound is thermally induced teratogenesis, which has been demonstrated in many animal species (chicken, mouse, rat, guinea pig, monkey) and apparently also occurs in humans. The nature and interpretation of such studies will be discussed. In therapeutic ultrasound, e.g., HIFU, the interest is in assuring the destruction of diseased tissue while sparing adjacent, healthy tissue. The concept of thermal dose will be described and used to quantify the probability and extent of biological effects expected from both diagnostic and therapeutic exposures. Additional factors relevant to thermal effects will also be considered, including the nature of the acoustic field in situ, as well as the state of perfusion and the variation in thermal sensitivity of the exposed tissue. It is concluded that adverse thermal events following diagnostic exposure are usually extremely rare, although there may be some reason for concern in a few special cases, while HIFU may induce significant collateral damage to proliferating cells pre- and postfocal zone.

Modelling the work to be done by Escherichia coli to adapt to sudden temperature upshifts

This paper studies and models the effect of the amplitude of a sudden temperature upshift DeltaT on the adaptation period of Escherichia coli, in terms of the work to be done by the cells during the subsequent lag phase (i.e., the product of growth rate mumax and lag phase duration lambda). Experimental data are obtained from bioreactor experiments with E. coli K12 MG1655. At a predetermined time instant during the exponential growth phase, a sudden temperature upshift is applied (no other environmental changes take place). The length of the (possibly) induced lag phase and the specific growth rate after the shift are quantified with the growth model of Baranyi and Roberts (Int J Food Microbiol 23, 1994, 277). Different models to describe the evolution of the product lambda x mumax as a function of the amplitude of the temperature shift are statistically compared. The evolution of lambda x mumax is influenced by the amplitude of the temperature shift DeltaT and by the normal physiological temperature range. As some cut-off is observed, the linear model with translation is preferred to describe this evolution. This work contributes to the characterization of microbial lag phenomena, in this case for E. coli K12 MG1655, in view of accurate predictive model building.

Methylxanthines binding with yeast total RNA in the presence of Mg 2+: a speed vac-centrifugation-facilitated solid-state Fourier transform infrared analysis

Interaction of naturally occurring methylxanthines (theophylline, theobromine, and caffeine) with yeast total RNA has been studied in presence of Mg to understand the modulation of its binding efficacy using Fourier transform infrared (FTIR) spectroscopy, wherein the samples were prepared by transforming the mixture from solution to solid-state employing speed vac centrifugation. The method was found to be a simple and short alternative for solution IR in studying RNA:drug/ligand interaction. The RNA and methylxanthines were complexed in 2:1 ratio in RNase-free water (made up to 1 ml in diethyl phosphoryl-pyrocarbonate-treated sterile microfuge tube) with different MgCl2 concentrations (1, 5, 10, and 35 mM); after a thorough mixing and overnight incubation at 37 C, the samples were concentrated by speed vac centrifugation (SC 110; Savant, USA) under normal physiological temperature and pressure. RNA– Mg and RNA–Mg–drug complexes were prepared and studied in solid-state using KBr pellet. It has been found that concentrating the samples by speed vac centrifugation does not affect the recovery; especially there has not been appreciable structural variation of samples (it is presumed that the transformation of the reaction state of molecules from solution to solid might cause drastic variation in RNA structure) observed as compared to that in the published papers [1,2]. Furthermore the IR spectrum obtained presently using the speed vac procedure leads to the elimination of water but does not lead to removal of ionic strength from the solution nor

Quantifying microbial lag phenomena due to a sudden rise in temperature: a systematic macroscopic study

The microbial lag phase is a complex and yet not completely understood phenomenon. Many studies on the microbial lag phase have been published but few report a systematic study; moreover, previous lag studies have involved the effect of multiple confounded factors. Here, the effect of sudden temperature rises on an exponentially growing Escherichia coli culture is systematically investigated. Experiments are performed in a computer-controlled bioreactor where E. coli K12 MG1655 is grown under aerobic conditions in Brain Heart Infusion (BHI) broth. This experimental set-up is used to characterise the effect of (i) the amplitude of the temperature shift, (ii) the pre-shift temperature level and (iii) the post-shift temperature level on the occurrence and length of a lag phase. Besides temperature, no other environmental changes take place at the moment of the temperature shift. To quantify the length of the induced lag phase, the experimental data are described with a common growth model. Depending on the three factors tested, a lag phase of more or less 1 h is induced or not. This lag/no lag behaviour can largely be explained by the existence of a normal physiological temperature range but also the amplitude of the temperature rise plays a role. It can be concluded that for the microorganism under study the lower boundary of the normal range lies approximately between 22.78 and 23.86 °C. It is shown that this boundary is no cut-off point, but rather a transition zone. Even more, repeated experiments at this boundary have yielded different results (lag or no lag). This observation points out that the mechanism triggering this lag phase is not absolute but may be subject to biological variability.

The effect of abrupt shifts in temperature on the lag phase duration of Escherichia coli and Klebsiella oxytoca

The effect of temperature of incubation on lag times of two gram-negative foodborne bacteria was investigated. Bacteria were instantaneously transferred between temperatures within and beyond the normal physiological temperature range (NPTR). Abrupt temperature shifts induced lag phases, but the degree of the response was dependent on the direction and magnitude of the shift. Temperature downshifts induced larger relative lag times (RLT; the ratio of lag time to generation time), than equivalent upshifts. The hypothesis of Robinson et al. [Int. J. Food Microbiol. 44 (1998) 83] that lag time can be understood in terms of the amount of work to be done to adjust to new environmental conditions and the rate at which that work is done was supported. Deviation of the reported proportionality between lag time and generation time was observed when late-exponential phase cells were subjected to abrupt temperature shifts from beyond the normal physiological range.

Physical Characteristics of Vivostat® Patient-Derived Sealant

This study compared the physical characteristics of Vivostat^® patient-derived sealant with two conventional fibrin sealants, Tissucol^® and Beriplast^®. Vivostat sealant exhibited greater elasticity without compromising tensile strength. Vivostat sealant polymerised at low temperatures (4 and 25°C) or at high temperature (70°C) exhibited similar viscoelastic properties as when polymerised at normal physiological temperature (37°C). Vivostat fibrin I solution can be stored at room temperature for up to 8 h without affecting the mechanical properties of the derived sealant. These physical characteristics of Vivostat patient-derived sealant suggest that it may have suitable stability and performance characteristics for use in a wide range of surgical procedures.

Ribosome-associated protein that inhibits translation at the aminoacyl-tRNA binding stage.

We have recently isolated and characterized a novel protein associated with Escherichia coli ribosomes and named protein Y (pY). Here we show that the ribosomes from bacterial cells growing at a normal physiological temperature contain no pY, whereas a temperature downshift results in the appearance of the protein in ribosomes. The protein also appears in the ribosomes of those cells that reached the stationary phase of growth at a physiological temperature. Our experiments with cell-free translation systems demonstrate that the protein inhibits translation at the elongation stage by blocking the binding of aminoacyl-tRNA to the ribosomal A site. The function of the protein in adaptation of cells to environmental stress is discussed.

Mild hyperthermia modulates biological activities of interferons

A significant enhancement of antiviral activity of human IFN-alpha, -beta and -gamma and murine IFN-gamma is observed when cells are treated with mild hyperthermia (39 degrees C) during antiviral assays. Treatment of primary human fibroblast cells with mild hyperthermia for 4 and 24 hours prior to interferon antiviral assays (pre-assay hyperthermia) further enhances interferon antiviral activity. An enhancement of interferon induced enzyme, 2,5-oligoadenylate synthetase, is also observed in cells treated with interferon and mild hyperthermia. This increase in enzyme activity is, in part, responsible for the observed increase in interferon antiviral activity with hyperthermia. Besides antiviral activity, mild hyperthermia also increases interferon antiproliferative activity on different tumour cells beyond its effect at normal physiological temperatures. On the other hand, mild hyperthermia decreases human interferon production in both human and murine cells when challenged with a viral or non-viral inducer. Also, mild hyperthermia suppresses interferon-mediated enhancement of natural killer (NK) cell activity in human and murine cells. The findings demonstrate that, although mild hyperthermia has suppressive effects upon interferon production and NK cell activity, it significantly increases both antiviral and antiproliferative activities of all three human interferons. These observations have direct bearing upon clinical utilization of exogenously administered interferons to late stage cancer patients who for the most part have a weaker immune system. In these patients, the antiviral and antiproliferative efficacies of administered interferon can be enhanced by combining interferon and hyperthermia.

Proton NMR chemical shifts and coupling constants for brain metabolites.

Proton NMR chemical shift and J-coupling values are presented for 35 metabolites that can be detected by in vivo or in vitro NMR studies of mammalian brain. Measurements were obtained using high-field NMR spectra of metabolites in solution, under conditions typical for normal physiological temperature and pH. This information is presented with an accuracy that is suitable for computer simulation of metabolite spectra to be used as basis functions of a parametric spectral analysis procedure. This procedure is verified by the analysis of a rat brain extract spectrum, using the measured spectral parameters. In addition, the metabolite structures and example spectra are presented, and clinical applications and MR spectroscopic measurements of these metabolites are reviewed.

Les récepteurs des protons et de la capsaïcine: Contribution à la physiologie et la physiopathologie de la douleur

The molecular cloning of two ligand-gated ion channels present in the primary afferent nociceptor terminal, i.e., the acid sensing ion channel ASIC and the capsaicin receptor VR1, was recently completed. ASICs are cationic channels rather selective for Na+ that are directly activated by a drop in the extracellular pH. They belong to the superfamily of amiloride-sensitive Na+ channels. They are composed of several homologous subunits, some of them being also present in the central nervous system, that can assemble in homo- or heteromultimers. A particular combination in the sensory neurons (ASIC2b and ASIC3) displays properties very close to that of the native channel involved in the perception of the non-adaptive pain associated with tissue acidosis. VR1 is a non-selective cationic channel that displays a high selectivity for Ca2+ and possess a structure different from that of ASIC but similar to that of store-operated channels (SOC). VR1 is specifically expressed in sensory neurons and is directly activated by vanilloid compounds like capsaicin. VR1 is also activated by noxious heat. The threshold for heat-evoked response is lowered by a decrease in the extracellular pH and VR1 is activated at normal physiological temperatures in the presence of low pH. The availability of these novel molecular probes will be important to study the pain mechanisms associated with these receptors and to develop new analgesic drugs that can modulate their activity.

Temperature stress for patients in routine magnetic resonance examinations

To determine energy exposure and temperature changes in routine magnetic resonance imaging practice. Body core and skin temperatures were compared in 155 persons (143 patients, 12 volunteers) undergoing routine magnetic resonance examinations with a 1.5 T field-strength magnetic resonance tomography unit using a fluoroptic temperature measurement system. Average applied energy was 0.3 W/kg for whole body and 1.92 W/kg for spatially localized SAR. The maximum whole-body SAR was 1.43 W/kg spatially localized. Body core temperatures differed from those of the control group by a median 0.1 degree C and only a few patients (16.8%) exceeded the limit (+/- 0.5%) at which regulatory mechanisms set in. All patients remained within the normal physiological circadian temperature range (+/- 1 degree C). Skin temperature rose a median 0.49 degree C, with a maximal increase of 5.31 degrees C, which may be considered to be within the limits of physiological temperature change. Clinically relevant warming of the body is unlikely in routine magnetic resonance imaging practice.

Effects of heat stress on mouse testicular cells and sperm chromatin structure.

Scrotal regions of mice were exposed to a 38.0, 40.0, or 42.0 degrees C (+/-0.1) H2O bath for 60 minutes to determine the effects of elevated temperatures on testicular cells and sperm chromatin structure. Mice were killed on various days after exposure, and ratios of acridine orange-stained testicular cell populations were determined by flow cytometry. Testicular weights of mice exposed to 42.0 degrees C decreased significantly day 1 (P < 0.01) through 35 (P < 0.001). Also, a significant relative decrease in testicular haploid cells was seen on days 3-35 (P < 0.001) with a corresponding increase in the diploid population (P < 0.001). Testicular analyses of mice exposed to 38.0 degrees C were not significantly different from control values. Testis weights of mice exposed to 40.0 degrees C were not affected, but a relative decrease in percent haploid cells occurred on days 11 and 14 (P < 0.001). The sperm chromatin structure assay (SCSA) was used to measure the susceptibility of cauda epididymal sperm DNA to in situ denaturation at low pH. Caudal epididymides of mice exposed to 42.0 degrees C had no sperm. Caudal epididymal sperm from mice exposed to 40.0 degrees C were most susceptible to acid-induced DNA denaturation on days 3 (P < 0.05), 7, 11, and 14 (all P < 0.001). The 38.0 degrees C exposed mice showed some minor sperm chromatin abnormalities at later time points (days 11-35). When compared to sperm head morphology measurements, SCSA parameters were more sensitive indicators of heat-induced sperm abnormalities. These results show that mouse spermatogenesis is disrupted by scrotal exposure to environmental temperatures several degrees over normal physiological temperature and, of more biological interest, that some thermal ranges above normal allowed production of sperm with compromised nuclear chromatin structure.

Basal level transcription of the human hsp86 gene is directed by intron-based elements.

The heat shock response includes the syntheses of three major size-classes of heat shock proteins (hsps) designated as class 20, 70 and 90 hsps, respectively. In contrast to the class 20 and 70 hsp genes, those coding for the class 90 hsps are already actively transcribed in the non-induced state. We have shown that the increased basal level transcription of the human hsp86 gene depends on the presence of the first intron. Furthermore, intron 1 of the hsp86 gene was also capable of conferring increased basal level transcription on the human hsp70 promoter. Finally, the intron I-based sequence elements of the hsp86 gene mediated an effective rescue of 5'-truncated hsp70 and hsp86 promoters. In contrast, such a rescue of inactivated promoters was not obtained with the viral SV40 gene enhancer which is often also capable of stimulating basal level expression. Element(s) which direct the basal transcription of the human hsp86 gene at normal physiological temperatures are located within the first intron of the gene. It is conceivable that this intron-dependent activation of basal hsp86 transcription reflects a fundamental requirement for this protein in the context of cellular growth and metabolism under non-stress conditions.

Ventilatory responses to temperature variation in the fresh water turtle, Mauremys caspica leprosa

A study of lung gas exchange in the fresh water turtle Mauremys caspica leprosa at normal physiological body temperatures (15, 25 and 35 °C) was extended to extreme temperatures (5 and 40 °C) to determine whether the direct relationship between body temperature and ventilatory response found in many lung-breathing ectotherms including other chelonian species was maintained. From 5 to 35 °C the lung ventilation per unit of O2 uptake and CO2 removed declined with temperature. Consequently, lung CO2 partial pressure increased with temperature. Its value was maintained within narrow limits at each thermal constant, suggesting a suitable control throughout the complete ventilatory cycle. At 40 °C the ventilatory response showed the opposite trend. The ratios of ventilation to lung gas exchange increased compared to their values at 35 °C. The impact of this increased breathing-lowering the estimated mean alveolar CO2 partial pressure-was nevertheless less than expected due to an increase in calculated physiological dead space. This suggests that the relative hyperventilation in response to hyperthermia found in Mauremys caspica leprosa is related to evaporative heat loss.