Increased flux of free radicals in cells subjected to hyperthermia: detection by electron paramagnetic resonance spin trapping.

It has been hypothesized that hyperthermia promotes oxygen-centered free radical formation in cells; however, to date there is no direct evidence of this heat-induced increase in oxygen free radical flux. Using electron paramagnetic resonance (EPR) spin trapping, we sought direct evidence for free radical generation during hyperthermia in intact, functioning cells. Rat intestinal epithelial cell monolayers were exposed to 45 degrees C for 20 min, after which the nitrone spin trap 5,5-dimethyl-1-pyrroline N-oxide (DMPO) was added. Compared to control cells at 37 degrees C, heat-exposed cells had increased free radical EPR signals, consistent with the formation of DMPO/.OH (aN = aH = 14.9 G). These findings indicate that heat increases the flux of cellular free radicals and support the hypothesis that increased generation of oxygen-centered free radicals and the resultant oxidative stress may mediate in part, heat-induced cellular damage.

Thermal ablation of canine prostate using interstitial temperature self-regulating seeds: new treatment for prostate cancer.

An interstitial temperature self-regulating implantable thermal seed for ablation of the prostate was investigated for the treatment of cancer. The technique is analogous to brachytherapy implants with three important advantages: highly localized temperatures may reduce complications, the thermal seed can be activated for retreatment at any point in time, and the seeds pose no radiation hazard to the clinical staff. Thermal seeds were implanted in the left lobe of the prostates in four dogs; the right lobe was a control to evaluate undesired heating outside the seed array. Linear-array thermometry probes were placed in both lobes, and the induction field for heating the implants was activated for 1 hour. After treatment, biopsies were taken from both lobes at 4-hour intervals up to 28 hours to evaluate thermal damage and thermotolerance as measured by expression of heat shock protein (hsp) 70. Only 5 minutes was required to heat the left lobe to 45 degrees to 55 degrees C. The maximum and minimum cumulative equivalent minutes at 43 degrees C (CEM43) thermal doses in the treated lobe were 174 and 4.4 hours, respectively; less than a 1-minute CEM43 was observed in the control lobe. Elevated hsp70 expression was detected in tissue of the treated lobe between 12 and 24 hours after treatment; minimal increases occurred in the control lobe. The thermal seed system was effective at heating the prostatic volume without damage to normal tissues outside the implant array, and subsequent treatments were simplified in comparison with other hyperthermia devices. Expression of hsp70 implies that retreatment of the prostate at intervals as short as 48 to 72 hours may avoid thermotolerance making weekly treatment an appropriate regimen.

HSP 70 induction and thermotolerance following interstitial hyperthermia in the dunning R3327 tumor in vivo.

We investigated the use of an interstitial temperature self-regulating implant for fractionated hyperthermia delivery for treatment of prostatic disease. Nonuniform heating, lower temperatures between the implants, and lingering thermotolerance for additional hyperthermia treatments are concerns associated with the technique. Thermotolerance of the Dunning R3327 prostate adenocarcinoma to a 1 hour interstitial heating of 42-43°C has been estimated using inducible heat shock protein (HSP) 72 as an assay. The duration of thermotolerance in a nonuniformly heated tumor is necessary for optimization of multiple-treatment planning. HSP 72 expression is increased between 8 and 16 hours posttreatment. Growth curves for conditioned (treated once at 42-43°C minimum) tumors retreated at a minimum temperature of 45°C after 10 hours recovery (where elevated HSP 72 expression is evident) were compared with those retreated after 48 hours recovery (with normal HSP 72 expression) and with conditioned controls; both retreatment groups differed from controls (p < 0.0001). Growth curves for tumors with elevated HSP 72 expression after 10 hours differed from those retreated after 48 hours (p ≤ 0.0202). The results indicate that in vivo measurement of HSP 72 expression in the Dunning tumor is an adequate indicator of thermotolerance for optimal sequencing of hyperthermia fractions and that sufficiently high thermal doses are effective against thermotolerant cell populations.

Effects of carbohydrate type and concentration and solution osmolality on water absorption.

We studied intestinal absorption of solutions containing either one (glucose, Glu, or maltodextrin, Mal) or two (fructose, Fru, and Glu or sucrose, Suc) transportable carbohydrate (CHO) substrates using segmental perfusion technique in eight healthy male subjects. These CHO were either free or directly transportable monosaccharides (Glu, Fru), bound as the disaccharide (sucrose, Suc), or as oligomers (maltodextrins, Mal). [CHO] was varied from 6% to 8% (120-444 mmol.1(-1)). All solutions contained low [Na+] (15-19 mEq) and [K+] (3-4 mEq). Solutions osmolalities varied from 165 to 477 mOsm.kg(-1). Osmolalities in the test segment ranged from 268 to 314 mOsm.kg(-1). The regression line of osmolality with water absorption differed for single as compared with multiple substrate solutions. The significantly different intercepts of these two regression lines suggest that solutions with multiple substrates produce greater water absorption at a given osmolality than those with one. Comparing all solutions, test segment solute flux (partial r = 0.69) was more important than mean osmolality (partial r = 0.32). In conclusion, solutions with multiple substrates stimulate several different solute absorption mechanisms yielding greater water absorption than solutions with only one substrate.

Tissue-specific HSP70 response in animals undergoing heat stress.

Heatstroke is a multisystem disorder that can result in death. Activities that increase the rate of heat storage predispose an organism to thermal injury. Using a 72-kDa heat shock protein (HSP72) as a marker of thermal injury, we determined 1) which organs synthesize HSP in animals after hyperthermia and 2) whether a high heating rate (HHR) resulted in more HSP72 than a low heating rate (LHR). Rats were assigned to either control, HHR (0.166 degrees C/min), or LHR (0.045 degrees C/min) groups. Heat exposure ended when colonic temperature (Tc) reached 42 degrees C. Total time in the heat and thermal load (measured as the time an animal maintained a Tc > 40.4 degrees C) were significantly lower in HHR compared with LHR animals. Hyperthermia resulted in a tissue-specific increase in HSP72 in the liver, small intestine, and kidney, but not in the brain or quadriceps muscles. In addition, HHR animals showed significantly greater accumulation of HSP72 in the liver compared with animals in the LHR group. Thus HSP72 synthesis is tissue specific at high physiological temperatures and may identify a critical target tissue susceptible to early thermal damage.

Heat shock protein response in a prostate tumor model to interstitial thermotherapy: implications for clinical treatment.

Hyperthermia is being utilized individually and in conjunction with other therapies in treating malignant and benign tumors, though few studies have examined cellular effects of elevated temperatures in the prostate model. Highly conserved proteins of the 70 kDa heat shock protein family (HSP 70) are produced in response to environmental stresses, including heat, and are found in all organisms. HSPs are an indicator of cell damage, are associated with thermotolerance, and provide cells with transient resistance to subsequent thermal challenges. Transient thermotolerance is important in the determination of temperature, duration, and sequencing for treatments. This preliminary study analyzes the HSP 70 response of the Dunning R3327 adenocarcinoma model to a single 50 degrees C 1 hr treatment. Elevated HSP levels were found between 10 and 16 hr, returning to baseline by 24 hr. As some fractions of the cells are able to produce HSP 70 following treatment, the data suggest that currently utilized clinical temperatures (42-46 degrees C) administered for 1 hr are inadequate. HSP levels in response to hyperthermia, radiation, and chemotherapy may be useful in finding optimal treatment regimens for prostate cancer.

Acute heat stress protects rats against endotoxin shock.

The purpose of this study was to determine 1) whether prior (24-h) heat stress could render rats cross-resistant to the lethal activity of bacterial lipopolysaccharide (LPS) and 2) whether this acquired state of resistance is associated with endotoxemia during the heat stress event. Four groups (n = 7/group) of rats were examined: 1) saline treated, 2) LPS treated, 3) heat stressed and saline treated, and 4) heat stressed and LPS treated. Saline or LPS (Escherichia coli, serotype 0111:B4, 20 mg/kg body wt) was given intravenously 24 h after exposure to heat (ambient temperature 47-50 degrees C, relative humidity 30%) for heat-stressed rats and at the same time of day for nonheated rats; survival was monitored for 48 h. Thermal responses were similar (P > 0.05); values for maximum core temperature (Tc) and time above Tc of 40 degrees C were 42.7 +/- 0.1 and 42.6 +/- 0.1 degrees C (SE) and 44.0 +/- 2.1 and 47.9 +/- 3.7 (SE) min for the heat-stressed saline-treated and heat-stressed LPS-treated rats, respectively. Administration of LPS to nonheated rats resulted in 71.4% (5 of 7 rats) lethality. In contrast, all (7 of 7) rats subjected to a single nonlethal heat stress event 24 h before LPS treatment survived (P < 0.05). Endotoxin was not detected in arterial plasma immediately after heat stress in rats (n = 6) exposed to a Tc of 42.9 +/- 0.1 degrees C. These findings demonstrate that acute heat stress can protect rats from the lethal activity of LPS.