The regulation of protein synthesis in the liver of rats. Mechanisms of dietary amino acid control in the immature animal

Weanling (23-day-old) rats were fed either on an amino acid-deficient diet (6% of casein, which in effect represents an ;amino acid-deficient' diet) or on a diet containing an adequate amount of protein (18% of casein) for 28 days. The hepatic cells from the animals fed on the low-protein diet were characterized by low amino acid content, almost complete inhibition of cell proliferation and a marked decrease in cell volume, protein content and concentration of cytoplasmic RNA compared with cells from control rats. The lower concentration of cytoplasmic RNA was correlated with a decreased ribosomal-RNA content, of which a larger proportion was in the form of free ribosomes. The protein-synthetic competence and messenger-RNA content of isolated ribosomes from liver cells of protein-deprived animals were 40-50% of those noted in controls. At 1hr. after an injection of radioactive uridine, the specific radioactivity of liver total RNA was greater in the group fed on the low-protein diet, but the amount of label that was associated with cytoplasmic RNA or ribosomes was significantly less than that noted in control animals. From these data it was concluded that dietary amino acids regulate hepatic protein synthesis (1) by affecting the ability of polyribosomes to synthesize protein and (2) by influencing the concentration of cytoplasmic ribosomes. It is also tentatively hypothesized that the former process may be directly related to the concentration of cellular free amino acids, whereas the latter could be correlated with the ability of newly synthesized ribosomal sub-units to leave the nucleus.

Extracorporeal whole body hyperthermia treatments for HIV infection and AIDS

Whole body hyperthermia therapy (WBHT) is the elevation of the core body temperature to 42 degrees C. In vitro studies have confirmed that 42 degrees C is cytocidal for virally infected lymphocytes, and even more effective when heating is repeated 4 days later. The safety and efficacy of two successive sessions of WBHT (4 days apart) was evaluated in 30 patients with AIDS (not on protease inhibitors), randomized to: 1) untreated controls, 2) low temperature WBHT for 1 hour at 40 degrees C and repeated 96 hours later, and 3) high temperature WBHT for 1 hour at 42 degrees C and repeated 96 hours later. The sorbent suspension in the ThermoChem System (HemoCleanse, West Lafayette, IN) system automatically controlled blood phosphate, calcium, and other electrolyte concentrations during WBHT. In 1 year of follow-up after WBHT, there were positive effects of the therapy on frequency of AIDS defining events, Karnofsky score, and weight maintenance. However, effects on plasma HIV RNA and CD4 counts were transient. Two successive WBHT treatments were performed in four patients who were on protease inhibitor/triple drug therapy, but had suboptimal response. In follow-up for 6 months, plasma HIV RNA and CD4 improved after WBHT, and the patients remained clinically well. This WBHT may have specific advantages in patients with suboptimal response to protease inhibitor therapy.

Effect of whole-body hyperthermia on AIDS patients with Kaposi's sarcoma: a pilot study

The safety and possible efficacy of extracorporeal whole-body hyperthermia (WBHT) were evaluated in the first FDA-approved feasibility study of WBHT in persons with AIDS. Six gay men, aged 20-50 years, CDC class C-3, underwent 1 h of WBHT at either 40 degrees C or 42 degrees C, employing a system that minimizes the physiological and biochemical changes that occur during WBHT. All subjects had Kaposi's sarcoma (KS), were free of opportunistic infections, and had significant elevations of plasma HIV RNA. During the treatment, there were no adverse side effects and all subjects tolerated WBHT without problems. KS lesions partially regressed immediately following WBHT in all subjects but returned to pretreatment status in five of six patients at 1 week. In subjects treated at 40 degrees C, CD4 counts decreased during the 8-week follow-up period; they remained unchanged, however, following 42 degrees C WBHT. Viral load remained unchanged following WBHT in subjects treated at 40 degrees C. Treatment at 42 degrees C resulted in an immediate reduction in HIV RNA that was not sustained at 1 week post-WBHT. We conclude that WBHT is safe in subjects with advanced HIV disease and that it may have a role in treating HIV infection. A larger controlled trial involving two treatments in less immunocompromised subjects is currently in progress to test this hypothesis.

Effect of heat on viral protein production and budding in cultured mammalian cells

The life cycle of enveloped viruses is intimately associated with, and influenced by, host cell membrane organization, which is altered by hyperthermia. Hyperthermia-modified Moloney murine leukaemia virus (M-MuLV) release, protein production and intracellular protein processing in a chronically infected cultured murine cell line, C9CL98 (C9). Both 44 degrees C/45 min and 42.8 degrees C/135 min substantially decreased cell-free viral env protein 8-48 h postheating, but virus release and cellular viral protein content increased following 42.8 degrees C/25 min. Proteolytic processing of viral Pr65 gag precursor to p30 gag protein, normally observed within unheated C9 cells, was blocked for at least 8 h after 44 degrees C/45 min. Virus released from heated C9 cells was as infectious to NIH/3T3 cells as was virus from control cells. Cells surviving exposure to 42.8 degrees C/135 min became thermotolerant to decreased virus release from a second heating if delivered 10-48 h after the initial heating. The mechanism by which virus release is blocked after hyperthermia remains to be elucidated.

Effects of heat and amino acid supplementation on the uptake of arginine and its incorporation into proteins in Escherichia coli

Hyperthermic treatment reduces protein synthesis and modifies amino acid transport in Escherichia coli. The present study examined the role of nutrient availability on these processes. Cultures of E. coli in log phase were aliquoted into growth medium with or without complete amino acid supplementation and exposed to 37, 44, or 48 degrees C for 10 min. Amino acid supplementation increased radiolabelled arginine uptake at 48 degrees C when compared with unsupplemented cells. Exposure to 48 degrees C also reduced protein synthesis in both groups by at least 50% as reflected by labelled arginine incorporation. Two-dimensional gel electrophoresis indicated that this heat-related decrement in synthesis was most apparent in basic proteins. Total density analysis of the fluorographs demonstrated reductions in basic proteins of 15% at 44 degrees C and 89% at 48 degrees C, while acidic proteins only showed an 80% reduction at 48 degrees C. Amino acid supplementation appears to raise the baseline, but not to modify the final results of hyperthermia-induced inhibition of protein synthesis. The sensitivity of basic protein synthesis seems to be a key event in this process.

Recent developments in the radiobiology of cellular membranes

We have reviewed the literature on cellular membrane radiobiology over the last ten years and, in particular, report on the development of rapid techniques used to identify damage soon after irradiation. It is clear that damage can now be quantified after low doses, and further refinements can be expected. From the work summarised, it would appear that changes to membranes at low doses may occur soon after damage to other important macromolecules by intercommunicating processes. We believe that there now exists a variety of rapid methods of measuring deposition of damage in vital macromolecules, such as cellular membranes and DNA, which can give a fuller picture of the overall effects of radiation and lead to predictions of eventual cellular mortality.

Shedding light on the use of heat to treat HIV infections

Considering the lack of effectiveness of current therapies to treat HIV disease, the authors present observations that provide a strong cogent argument for critically designed and meticulously performed clinical trials employing whole body hyperthermia with or without other therapeutic modalities. Only as a result of such clinical trials will it be possible to fairly evaluate the role of hyperthermia as a potential therapy for treatment of chronic HIV infection.

Role of cellular membranes in hyperthermia: some observations and theories reviewed

We have re-examined critically the evidence for and against the involvement of membranes in determining the response of cells to acute and chronic heat stress. Although frequently dismissed by many in the past, we believe that the bulk of evidence presented supports the view that physical and compositional alterations of membrane lipid components, both during and subsequent to heat exposure may, at least in part, account for cell adaptation, malfunction and lethality. Our primary goal in this review is to generate renewed interest in testing the validity of this hypothesis.

Effect of diet on hyperthermia-induced cell lethality and prostaglandin release

Hyperthermia-induced cell lethality is thought to be mediated through injury to the cell membrane. Membrane perturbation results in the release of prostaglandins (PG) and leukotrienes (LT). These compounds are potent biological mediators and may modify the tumor microenvironment and therapeutic efficacy. Membrane composition and PG/LT release are influenced by the dietary fatty acids. The relationship between these variables and response to hyperthermia was examined in vitro using murine P388 leukemia cells grown as an ascites in mice provided either saturated fatty acid diet (SFA; 16% beef tallow) or unsaturated fatty acid diet (UFA; 16% safflower oil). Cells were harvested and exposed in vitro to either 37 degrees C or 43.5 degrees C for periods up to 2 hours. Hyperthermic exposure for 2 hours resulted in 40% cell lethality in SFA cells and 55% in UFA cells. The phospholipid and total cholesterol content was higher (33% and 50% respectively) in the UFA versus the SFA cells. Hyperthermia produced a six-fold increase in prostaglandin E2 PGE2 release by SFA cells and a 4.5-fold increase by UFA cells. No LTC4 was detected. Alteration of dietary fat affects cell lethality and PG release following hyperthermic treatment. The increase in phospholipid and cholesterol content of UFA cells may be a response to reduced membrane fluidity.

Concentration-dependent increase of murine P388 and B16 population doubling time by the acyclic monoterpene geraniol

Geraniol, an acyclic end product of a plant isoprene pathway and a pyrophosphorylated intermediate in plant and animal pathways, caused a concentration-dependent increase in the population doubling time of murine P388 leukemia cells in suspension culture and of B16 melanoma cells in monolayer culture. The suppression of the growth of P388 cells by geraniol (0-0.9 mM) and by mevinolin (0-0.25 microM), a competitive inhibitor of mevalonate biosynthesis, was reversed by the addition of 0.5 mM mevalonolactone to the growth medium. Flow cytometry of asynchronous B16 cells grown with geraniol (0-0.15 mM) revealed a population characterized by larger cells with altered nuclear characteristics. Over the course of four studies, dietary geraniol increased the 50% survival time of mice by 10, 29, 33, and 50% following the i.p. transfer of P388 cells. The results of the latter study showed that, following the i.p. transfer of 1 x 10(5) P388 cells, the control group of female C57BL x DBA/2 F1 mice had a 50% survival time of 24 days and a maximum survival of 27 days. Mice fed a diet containing 0.1% geraniol for 14 days prior to and following the P388 cell transfer had a 50% survival time of 36 days, and 20% of the mice remained free of tumors during the 50-day trial. These studies support the possibility that monoterpenes and other isoprenoid products of plant metabolism are in part responsible for the anticarcinogenic actions of diverse fruits, vegetables, and cereal products.

Effects of heat and other agents on amino acid uptake in Escherichia coli

In Escherichia coli K1060 grown at 37 degrees C we observed that the uptake of both L-[3H]leucine and L-[35S]methionine was inhibited by exposure of the cells to 48 degrees C. The calcium channel blockers diltiazem and verapamil, and the anti-arrhythmic agent quinidine, inhibited the uptake of L-[3H]leucine at both 37 degrees C and 48 degrees C. Verapamil also inhibited the uptake of L-[35S]methionine at 37 degrees C, but at 48 degrees C protected against some of the heat-induced decrease in the uptake of this amino acid. The local anaesthetic procaine markedly inhibited the uptake of both labelled amino acids at temperatures between 37 degrees C and 48 degrees C. Amino acid uptake and cell killing were not correlated.

Effects of decreased pH on membrane structural organization of Escherichia coli grown in different fatty acid-supplemented media: a 31P NMR study

Total membranes from Escherichia coli cells grown in different fatty acid-supplemented media have been examined by 31P NMR at different pH values. The isolated inner and outer membranes were also studied and compared to the liposomes formed with the corresponding extracted lipids. While the liposomes show structures that are correlated with lipid composition, degree of fatty acid unsaturation, and pH, the membrane structure is mainly bilayer. The presence of two bilayer phases characterized by different chemical shift anisotropy values (delta nu csa) is detectable at neutral pH; a perturbation of the bilayer phase characterized by the smallest delta nu csa is produced by low pH. Moreover, an isotropic peak is always present in the membrane NMR spectra: its attribution to cardiolipin molecules is discussed on the basis of digestion experiments with phospholipase C.

An approach to AIDS therapy using hyperthermia and membrane modification

Altering the biophysical characteristics of cell membranes by diet and membrane perturbing agents markedly influences thermosensitivity of cells. Likewise, manipulation of viral envelopes either by altering their lipid composition by diet or by the use of agents that perturb the lipid envelope influence infectivity of enveloped viruses and the progression of viral disease. The use of hyperthermia and envelope modification as a combined approach to treat AIDS has until now neither been suggested nor attempted. On the basis of my previous work and a review of the literature, I theorize that the combination of hyperthermia with procedures designed to alter the viral envelope will likely result in an increased viral sensitivity and be useful clinically for treatment of patients with enveloped viral diseases such as AIDS.

Major E. coli heat-stress protein do not translocate: implications for cell survival

When Escherichia coli are exposed to heat stress, the majority of proteins in the process of synthesis at the time of heat stress are rapidly translocated to the outer membrane of the bacterium. The synthesis of most of these proteins appears to take place on membrane-bound polyribosomes. With the temperature shift, overall protein synthesis is inhibited while the synthesis of a small group of proteins is initiated. These proteins are not translocated, but remain in the cytosolic compartment, and they are identifiable as heat-stress proteins. Both the translocation phenomenon and the retention of heat-stress proteins in the cytosolic compartment in proximity to the nucleoid could counteract the effects of heat stress. The translocated proteins may operate by stabilizing the outer membrane prior to the induction of heat-stress proteins and the latter, which are confined to the cytoplasmic compartment, may serve to protect the integrity of the nucleoid structures.

Influence of membrane-lipid composition on translocation of nascent proteins in heated Escherichia coli

In studies using Escherichia coli we have shown that new protein species appear in the outer membrane fraction with concomitant losses of nascent proteins from the soluble and inner membrane fractions following heat exposure. Of the various explanations for this phenomenon, temperature-induced membrane disorganization appeared the most likely. It is suggested that heat mimics the action of the signal sequence of a protein on the lipid bilayer allowing non-signal-sequence-containing proteins to be translocated. To test this hypothesis we grew E. coli K1060 cells, an unsaturated fatty acid requiring auxotroph, supplemented during growth with fatty acids of varying chain length in an attempt to determine whether biological membranes of varying ability to maintain their bilayer configuration could be constructed. The rationale being that such membranes would allow us to determine whether differences in translocation would occur in cells grown at the same temperature supplemented with either 16:1 or 20:1 unsaturated fatty acids when the cells were subjected to a series of thermal insults. Protein translocation occurred to a greater extent and at lower temperatures in cells supplemented with the longer chain fatty acid. Treatment of outer membranes with either 1 M salt, 6 M urea or high pH and studies determining fluorescent polarization values by scanning up and down through a series of temperatures ranging from 15 to 49 degrees C indicate that the proteins translocated by heat to the outer membrane are integral. Protein translocation may represent an adaptive response to an altered environment enabling the cell to respond to stress by stabilizing its outer membrane.

Influence of protein nutrition on dose-survival relationship following rat kidney irradiation

Immediately following unilateral nephrectomy the remaining kidney of juvenile male Sprague-Dawley rats was sham irradiated or irradiated to doses of 14-30 Gy. Following irradiation the animals were placed on isocaloric diets of either 20 or 4% protein. Median life spans for the animals on the low protein diet were significantly increased compared to the median life spans on the 20% protein diet. Serum urea nitrogen (SUN) levels were periodically measured in rats from each of the experimental groups. SUN levels in the irradiated rats fed the 20% protein diet increased significantly over unirradiated controls as a function of time. In contrast animals fed the 4% protein diet showed no significant changes in SUN levels irrespective of the size of radiation dose and time post irradiation. Renal protective factors calculated as the ratio of 80% survival times for animals fed the 20% protein diet compared to animals fed the 4% protein diet can be calculated to be 2.3 at 18 Gy and 2.8 at 22 Gy. Likewise, a SUN protective factor calculated as the ratio of percentage of nonirradiated control SUN values for the two diets (SUN 20% irradiated) (SUN 20% nonirradiated) (SUN 4% irradiated) (SUN 4% nonirradiated) is 2.4 for 18 Gy and 3.9 for 22 Gy.

Translocation of nascent non-signal sequence protein in heated Escherichia coli

Exposure of Escherichia coli to heat resulted in 1) selective inhibition of protein synthesis, 2) synthesis of heat shock proteins, and 3) altered subcellular distribution of newly synthesized proteins. Either 5 min or 1 h at 48 degrees C increases outer membrane proteins of Coomassie Blue-stained gels. After 1 h, there was a loss of stained proteins from the soluble fraction. Much greater changes in the distribution of radiolabeled (newly synthesized) proteins were observed, with marked increases in the number of outer membrane protein species and a corresponding loss of soluble fraction proteins. Three major species of radiolabeled proteins from heat-treated cells remain in the soluble fraction; these proteins have apparent Mr 56,000, 69,200, and 79,400. Cells were labeled with L-[35S] methionine at either 37 or 48 degrees C and chased with non-radiolabeled methionine before a temperature shift to either 48 or 37 degrees C, respectively. Only proteins synthesized at elevated temperature participated in translocation. It is suggested that heat disordering of membrane lipids promotes interlipidic connections between the inner and outer membrane providing pathways for protein movement to the outer membrane and may be the mechanism whereby a cell quickly responds to environmental temperature stress. The response does not require but may trigger synthesis of mRNA.

Increasing the thermosensitivity of a mammary tumor (CA755) through dietary modification

Disruption of the integrity of tumor cellular membranes has been proposed as an initiating event in hyperthermic cell death. Thermosensitivity measured by the shift in the harmonic mean of tumor regrowth delay of CA755 mammary adenocarcinomas grown in the hind legs of male BDF1, mice increased 22% when the hosts were fed a diet enriched in polyunsaturated fatty acids. Although the diet elicited the anticipated increase in tumor membrane phospholipid polyunsaturated fatty acids, the proportion of total unsaturated fatty acids decreased and the proportion of membrane-rigidifying saturated fatty acids increased. Concomitantly, the concentrations of cholesterol and phospholipid phosphorus increased and the ratio of phosphatidylethanolamine to phosphatidylcholine decreased, presumably to counter the effect of the change in the fatty acid pattern. In host liver membranes, the diet-mediated increase in proportion of polyunsaturated fatty acids was not accompanied by an increase in the proportion of rigidifying saturated fatty acids. Instead, the homeoviscous adaptation consisted of decreases in monounsaturated fatty acids and cholesterol concentration and an increase in the phosphatidylethanolamine-phosphatidylcholine ratio. Addition of a natural inhibitor of cholesterol biosynthesis to the polyunsaturated fatty acid enriched-diet reversed the diet-mediated increase in the phosphatidylethanolamine-phosphatidylcholine ratio of host liver membranes. Tumor membrane lipids from hosts fed the combined dietary factors were characterized by the formentioned rigidifying increase in saturated fatty acids and compensatory decrease in the phosphatidylethanolamine-phosphatidylcholine ratio. The inhibitor reversed the compensatory increases in cholesterol and phospholipid phosphorus concentrations. As a consequence the thermosensitivity of tumors bearing this perturbed membrane was increased.

Hyperthermic sensitivity and growth stage in Escherichia coli

Hyperthermic sensitivities of Escherichia coli B/r and Bs-1 were determined for lag-, midlog-, and stationary-phase cells at 47, 48, and 49 degrees C. In both strains midlog-phase cells were strikingly more heat sensitive (100-fold greater killing after 4 h at 48 degrees C) than stationary-phase cells, with intermediate sensitivity for lag-phase cells. In contrast to the reported difference in the radiation sensitivity between these two strains, very little difference in heat sensitivity was seen. Patterns of fatty acid composition of both strains were very similar at each phase of growth. From midlog to stationary phase, 16:1 and 18:1 unsaturated fatty acids decrease from 16 and 30% to 0.5 and 3%, respectively, while the C17 and C19 cyclopropane fatty acids increase from 7 and 3% to 22 and 25%, respectively. Concomitant with these changes in fatty acid composition, substantially higher membrane microviscosity values were recorded for stationary-phase cells. Total membrane microviscosity was positively associated with the C17 and C19 cyclopropane fatty acid composition and with cell survival following hyperthermia. In contrast to hyperthermic sensitivity, radiation survival differences between B/r and Bs-1 are little affected by growth stage. We propose that these results are consistent with a critical influence of membrane lipids on cellular hyperthermic sensitivity and further that the target sites for radiation and hyperthermia are different in these cells.

Radiosensitivity of peripheral blood lymphocytes in autoimmune disease

The proliferation of peripheral blood lymphocytes, cultured with Con A, can be inhibited by ionizing radiation. Lymphocytes from patients with conditions associated with autoimmunity, such as rheumatoid arthritis, systemic lupus erythematosus and polymyositis, are more radiosensitive than those from healthy volunteers or patients with conditions not associated with autoimmunity. The nuclear material isolated from the lymphocytes of patients with autoimmune diseases is, on average, lighter in density than the nuclear material from most healthy controls. This difference in density is not related to increased sensitivity to ionizing radiation but the degree of post-irradiation change in density (lightening) is proportional to the initial density, i.e. more dense nuclear material always shows a greater upward shift after radiation. The recovery of preirradiation density of nuclear material, 1 h after radiation exposure, taken as an indication of DNA repair, correlates with the radiosensitivity of lymphocyte proliferation (Con A response); failure to return to pre-irradiation density being associated with increased sensitivity of proliferative response. These results require extension but, taken with previously reported studies of the effects of DNA methylating agents, support the idea that DNA damage and its defective repair could be important in the aetio-pathogenesis of autoimmune disease.

Potentiation of differential hyperthermic sensitivity of AKR leukemia and normal bone marrow cells by lidocaine or thiopental

Previous work has utilized spleen colony formation to evaluate the fractional survival of AKR leukemia and normal bone marrow cells after in vitro heat exposure. An inherently greater sensitivity of neoplastic cells to thermal killing, as compared to normal syngeneic stem cells, has been established both at 41.8 degrees C and 42.5 degrees C. Normal bone marrow colony-forming units were assayed in lethally irradiated (750 cGy) mice. Leukemic colony-forming units were assayed in nonirradiated mice. Using this methodology, the authors demonstrated that the differential effect of hyperthermia on AKR murine leukemia and AKR bone marrow cells can be further enhanced by the addition of lidocaine or thiopental to incubation mixtures. These findings may have application to autologous bone marrow transplantation in humans.

Effect of hyperthermia and gamma-radiation on Escherichia coli K1060 D-lactate dehydrogenase

The response of E. coli K1060 D-lactate dehydrogenase (D-LDH), an enzyme located in the cytoplasmic membrane, was studied following 42.5 degrees C hyperthermia and/or gamma-irradiation. The inactivation of D-LDH following the above treatment was used as a tool to probe the role of membrane proteins in the radiation and/or heat sensitivity of cells. No correlation between loss of enzyme activity and cell killing was found, suggesting that D-LDH does not play an important role in hyperthermic cell survival. The results obtained in combined hyperthermia and gamma-irradiation treatments on loss of D-LDH activity and E. coli cell killing suggest that an interaction between heat and radiation occurs at the membrane structure level. Moreover, when cells were heated at 42.5 degrees C in the presence of 10 mM procaine-HCl, both cell killing and loss of D-LDH activity were enhanced. The involvement of membrane structure in the heat sensitivity of cells is strongly indicated by the latter observations. The opposite effect was observed when procaine was present during irradiation in oxic conditions, suggesting that procaine itself can also act as a scavenger towards OH-induced radicals.

pH-sensitive liposomes: acid-induced liposome fusion

Sonicated unilamellar liposomes containing phosphatidylethanolamine and palmitoylhomocysteine fuse rapidly when the medium pH is lowered from 7 to 5. Liposome fusion was demonstrated by (i) mixing of the liposomal lipids as shown by resonance energy transfer, (ii) gel filtration, and (iii) electron microscopy. The pH-sensitive fusion of liposomes was observed only when palmitoylhomocysteine (greater than or equal to 20 mol%) was present in the liposomes. The presence of phosphatidyl-ethanolamine in the liposomes greatly enhanced fusion whereas the presence of phosphatidylcholine inhibited fusion. During fusion of liposomes containing phosphatidylethanolamine and palmitoylhomocysteine (8:2, mol/mol), almost all of the encapsulated calcein was released. Inclusion of cholesterol (40 mol%) in the liposomes substantially decreased leakage without impairing fusion.

Radio- and thermosensitivity of E. coli K1060 after thiol depletion by diethylmaleate

The Escherichia coli auxotroph K1060 has been grown in a medium supplemented with either oleic acid (18:1) or linolenic acid (18:3) and its radiosensitivity and thermosensitivity established using bacterial cell survival as the assay system. No difference in radiosensitivity was observed when oleic and linolenic grown cells were exposed to gamma-radiation at room temperature. When heated at 49 degrees C linolenic grown cells were more sensitive than oleic grown cells. To investigate whether soluble -SH compounds, e.g., glutathione (GSH), were critical in protecting cells against radiation or heat, studies were performed using cells depleted of -SH by incubation with diethylmaleate (DEM). After reduction of water-soluble non-protein thiol compounds to 25% (10 mM DEM treatment) of control value, no major changes in radiosensitivity under oxic conditions were found. Radioresistance increased slightly when irradiation was performed under hypoxic conditions. Thermoresistance was clearly stimulated after DEM treatments between 1 and 10 mM DEM. The main conclusion of these experiments is that lowering the cellular level of reduced glutathione may not generally be correlated with a higher radio- and thermosensitivity.

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.

Lowered pH eliminates the enhanced hyperthermic killing of E. coli induced by procaine or exposure to N2 gassing

Survival of E. coli K1060 is enhanced when they are heated at 47 degrees C in pH 6 medium as compared to pH 7.4. At pH 6 nitrogen bubbling and 10 mM procaine did not increase hyperthermic killing. The membrane content of phosphatidylethanolamine is about 80 per cent of the total of phosphatidylethanolamine, phosphatidylglycerol and cardiolipin phospholipids. The polar headgroup of this lipid is highly sensitive to pH changes in this pH range. The changes in electrostatic charge with its secondary effects on membrane-protein relationships may explain resistance to hyperthermic killing. Thus, the difference in response to lowered pH of bacterial, compared to mammalian cells may be revealing membrane-related phenomena critical to hyperthermic killing. Also increased levels of cardiolipid were observed in linolenic acid grown cells which could be an 'attempt' to stabilize their membranes.

Systemic lidocaine enhancement of hyperthermia-induced tumor regression in transplantable murine tumor models

Previously, we reported that local lidocaine infusion of a CA 755 mammary adenocarcinoma growing in C57BL X DBA/2 F1 mice, when combined with local heating for 1 hr in a 43.5 degrees water bath, significantly increased survival and inhibited tumor growth more than heating alone. Because of its clinical implications, systemic lidocaine was tested in the above model system and in a murine fibrosarcoma tumor model. An equivalent supraadditive, tumor-inhibitory effect of heat and lidocaine was obtained with both systemically and intratumor-administered lidocaine. The serum levels of lidocaine necessary to achieve tumor regression were within the therapeutic range for the control of arrhythmia in humans. Several treatment schedules, varying the mode of drug delivery, were evaluated. The effects of treatment on tumor growth characteristics were analyzed using an extension of the Cox survival model.

Biological optimization of hyperthermia: modification of tumor membrane lipids

The sensitivity of the solid mammary adenocarcinomas CA755 and MtGB, grown in the medial aspect of the hind legs of host mice, to local hyperthermia (43.5 +/- 0.1 degrees C for 1 hr) was increased by feeding the host mice a diet enriched in linoleic acid. The enhanced sensitivity was expressed only when the diet was fed for 15 days prior to the tumor transfer. Infusion of lidocaine into the tumor immediately before the hyperthermic exposure enhanced the thermal sensitivity of the controls but not of the linoleic acid-enriched tumors. Sensitivity was analyzed by tumor growth rates and growth delay following exposure. The fatty acid patterns revealed that the proportion of polyunsaturated fatty acids (20:4 and 22:6) decreased reciprocally with increased linoleic acid in the liver phospholipids, whereas in the tumor all polyunsaturated fatty acids increased at the expense of monounsaturated fatty acids. These studies suggest that dietary lipids affected tumor cell sensitivity to hyperthermia.

Cholesteryl hemisuccinate alters membrane fluidity, angiotensin receptors, and responses in adrenal glomerulosa cells

We examined the effects of cholesteryl hemisuccinate on membrane fluidity and angiotensin II (AII) actions in bovine adrenal glomerulosa cells. Incubating cells with cholesteryl hemisuccinate decreased membrane fluidity and markedly inhibited AII binding. The effect on binding was characterized by a decrease in AII receptor number. The effects of AII on phosphatidyl inositol turnover and calcium fluxes, proposed intermediaries of AII actions on aldosterone secretion, were less impaired than AII binding by cholesteryl hemisccinate. AII stimulation of aldosterone secretion was preserved despite the decrease in AII binding after cholesteryl hemisuccinate treatment. These results indicate that AII binding can be dissociated from its effects on aldosteronogenesis by a reagent that alters membrane fluidity.

Structural changes in murine cancer associated with hyperthermia and lidocaine

Hyperthermia alone and hyperthermia with lidocaine cause changes in the fine structure of the CA755 tumor cell as well as the breakdown of the tumor vasculature. The first structural change, observed immediately after termination of hyperthermia of 43.5 degrees for 1 hr, is the vesiculation of the Golgi apparatus. Other structural changes occur later but with variable times of onset. The changes appear to be unrelated to the presence of lidocaine. Vascular breakdown results in hemorrhaging within the tumor, and its onset and intensity appear to vary directly with the size of the tumor. Breakdown of the tumor cell plasmalemma and degenerative changes of the cytoplasm and nucleoplasm are seen more frequently in large tumors and in the interior of small tumors at any given time after the end of hyperthermia. The vesiculation of the Golgi persists in treated cells for as long as 30 hr. This modification may represent an intensification in the function of the Golgi apparatus; however, it closely corresponds to that found in a variety of other cells treated with a class of compounds, including lidocaine, that specifically inhibits the function of the Golgi apparatus. The effect of these compounds is rapidly reversible, unlike hyperthermia. Since the Golgi apparatus probably is crucial in repairing any deleterious effects of hyperthermia, any impairment of its normal function would place most treated tumor cells in a difficult position. The rate of tumor destruction may ultimately depend on the breakdown of the tumor vasculature following hyperthermia and lidocaine.

Correlation of bacterial hyperthermic survival with anaesthetic potency

We have evaluated several local anaesthetics and hypnotics for their relative ability to influence hyperthermic cell killing. Bacterial cell survival following exposure to heat and anaesthetic was used as the assay system. The E. coli bacterium used was the unsaturated fatty acid auxotroph, K1060. It was grown at 37 degrees C in medium supplemented with oleic acid and then exposed to 47 degrees C hyperthermia in the presence of an anaesthetic. The local anaesthetics tested were procaine, lidocaine, tetracaine, and benzocaine, and the general anaesthetics were barbital and pentobarbital. The dose response for each anaesthetic was determined over a five-hour heating period. The anaesthetic concentration required during heating to halve the time for cell killing found with heat alone is 5.9 mM for procaine, 0.8 mM for lidocaine, 0.12 mM for tetracaine, 2.0 mM for benzocaine, 6.7 mM for barbital and 1.2 mM for pentobarbital. There is a direct correlation between equivalent effect doses of the local anaesthetics and published data for the relative potency of the same anaesthetics as determined by respiratory arrest in mice and by myocardial contractile force in dogs. The assay we have described would be a convenient and easy test for the interaction of these drugs with hyperthermia. The use of this interaction with hyperthermia as an adjuvant in combined radiation-hyperthermia therapy should be tested.

Influence of dietary protein levels on survival of rats following kidney irradiation

Concern about radiation induced nephropathy results in a dose limiting constraint in some applications of radiation therapy. An understanding of the etiology of radiation therapy. An understanding of the etiology of radiation nephropathy is essential if attempts to alter the time course or extent of the pathology are to be successful. In an attempt to gain a better understanding of this disease process, and to see if it could be altered by dietary manipulation, young adult male Sprague-Dawley rats were unilaterally nephrectomized, after which the remaining kidney was exteriorized and exposed to 14 Gy of X rays. Non-irradiated control animals had their remaining kidney exteriorized for a comparable length of time. Five days after irradiation, the animals were switched from standard lab rations to isocaloric diets of differing protein content. Diets used included 4%, 20% and 50% protein and the 4% and 20% diets given in combination with 0.9% NaCl drinking water. For all the diet groups, irradiated animals had median survival times shorter than their corresponding non-irradiated controls. Within the irradiated groups, the ranking of the median survival times was: 4% + 0.9% NaCl greater than 4% greater than 20% + 0.9% NaCl = 20% greater than 50%. The differences in survival among the irradiated groups were significant at the 0.01 level. These data indicate that kidney response to irradiation can be altered by manipulation of dietary protein levels. Such information may have clinical application.

Clinical prospects for liposomes

The use of liposomes has recently been the subject of considerable attention as a promising and versatile approach to drug delivery. Particularly intriguing is the possibility of targeting liposomes to specific areas of the body such as tumors or sites of inflammation or parasitic invasion for either local accumulation or release of associated drugs. This review focuses mainly on recent in vivo work having clinical potential. An extensive discussion of liposome preparation and entrapment of drugs for controlled release in vivo is also included. The stability of liposomes in biological fluids is a major problem. The mode of administration, either intraperitoneal, subcutaneous, local, oral, or respiratory, is closely related to the life of the liposomes in vivo. Following in vivo administration the lifetime of a liposome is critically dependent on its composition, size, and charge. Liposome toxicity appears to be minimal, but should be considered when administering liposomes to patients. Tissues such as the liver, spleen, and lungs, because of macrophage ingestion of liposomes, become potential sites of drug toxicity. The use of liposomes to deliver antiparasitic drugs in the treatment of malaria and leishmaniasis is promoting; so it is the use of surfactant-carrying liposomes in the treatment of respiratory distress syndrome in premature babies. Recent cancer studies utilizing liposomes both in vivo and in vitro have shown promise. In tumor-bearing animals a liposome drug delivery system has caused a regression, delayed tumor growth, and increased survival time. Although the clinical use of liposomes is only in its infancy, its potential in future therapy appears promising.

Differential response to heat of metastatic and non-metastatic rat mammary tumors

Metastasizing and non-metastasizing transplantable mammary tumors were implanted into female W/Fu rats. A pair of tumors were employed, the SMT-2A and MT-W9B. When these tumors were exposed to water bath heating at 43.5 degrees C for 60 minutes, a significantly longer tumor-free growth delay was obtained in the metastasizing tumor compared to its non-metastasizing counterpart. The protein to phospholipid ratio and the content of arachidonic acid was lower in the metastasizing tumor than in the non-metastasizing one. By way of apparent compensation, the metastasizing tumor contained more linoleic and stearic acid. These observations suggest a relation between metastasizing capacity, thermal sensitivity, and membrane composition.

Selective delivery of liposome-associated cis-dichlorodiammineplatinum(II) by heat and its influence on tumor drug uptake and growth

In an attempt to optimize the chemotherapeutic treatment of mouse tumor Sarcoma 180, liposomes containing cis-dichlorodiammineplatinum(II) (PDD), having transition temperatures of few degrees higher than the rectal temperature of mice, were used in combination with local hyperthermia. The uptake of radioactive PDD by tumors heated for 1 hr at 42 degrees was almost four-fold greater when the drug was associated in liposomes than if administered as free drug. Uptake of liposome-administered radioactive platinum by liver was twice that obtained with free PDD, whereas its incorporation by the kidney was the same by either method of drug administration. The effect of various combinations of hyperthermia, drug-containing liposomes, and free PDD on tumor growth was also studied. Treatment with liposome-associated PDD plus local heating resulted in a dose-modifying factor of 7 when compared with free drug and no hyperthermia. The dose-modifying factor was 2.5 when PDD liposomes and heat were compared within free drug and heat. Thus, PDD could be specifically released from liposomes by heat and resulted in both a greater drug uptake and a delayed tumor growth following treatment. Potential normal tissue toxicity problems, however, still need to be resolved before clinical application of this combined modality will be possible.

Correlation of hyperthermic sensitivity and membrane microviscosity in E. coli K1060

We have demonstrated a positive correlation between membrane microviscosity and the temperature required to kill E. coli. Batches of cells with differing unsaturated fatty acid (u.f.a.) compositions were prepared from the u.f.a.-requiring E. coli K12 mutant K1060. The membrane microviscosity of these cells is estimated from the extent of fluorescence polarization of the probe molecule 1,6-diphenyl-1,3-5,-hexatriene dissolved in the membrane. For the same growth temperature, cells grown in oleic acid (18:1) have a greater microviscosity and u.f.a. content than linolenic acid (18:3) grown cells. the rate of decrease in microviscosity with increasing temperature is correlated with the amount of u.f.a. present in the membrane. From survival curves determined at several hyperthermic exposures, one can interpolate the hyperthermic temperature required to kill 90 per cent of the cells in three hours. These equivalent kill temperatures are directly related to the cell microviscosity. These data support the hypothesis that cell membrane microviscosity plays a critical role in hyperthermic killing.

Hyperthermia and surface morphology of P388 ascites tumour cells: effects of membrane modifications

The quantitative distribution of cell surface alterations of heated P388 ascites tumour cells was determined by scanning electron microscopy. Cells harvested from host animals maintained on a standard rodent chow diet or one high in saturated fatty acids responded differently, to identical hyperthermic treatment in vitro, to cells obtained from animals on a highly unsaturated diet. The morphological response of cells from chow fed animals was modified by addition to the incubation medium, of procaine, a membrane-active drug. The pattern of response observed after these cells were heated in the presence of procaine resembled that seen following heat treatment of ascites cells obtained from animals fed diet high in unsaturated fatty acids. These data are consistent with the hypothesis that a cell's response to hyperthermic insult is related to its membrane fluidity at the time of treatment.

pH-sensitive liposomes: possible clinical implications

When pH-sensitive molecules are incorporated into liposomes, drugs can be specifically released from these vesicles by a change of pH in the ambient serum. Liposomes containing the pH-sensitive lipid palmitoyl homocysteine (PHC) were constructed so that the greatest pH differential (6.0 to 7.4) of drug release was obtained near physiological temperature. Such liposomes could be useful clinically if they enable drugs to be targeted to areas of the body in which pH is less than physiological, such as primary tumors and metastases or sites of inflammation and infection.

The influence of membrane fluidity on radiation induced changes in the DNA of E. coli K1060

E. coli K1060 a fatty acid auxotroph unable to synthesize unsaturated fatty acids was used to study the effect of membrane fluidity on survival and DNA damage after exposure to ionizing radiation. Oleic and elaidic acids were incorporated into the bacteria and the temperatures of irradiation chosen in order to give the maximum difference in survival between the "liquid crystal" and "gel" states. Maximum sensitization was achieved by cooling the bacteria for 5 min at ice temperature before irradiation. No sensitization was observed if cooling was after irradiation. Under non-nutrient conditions both oleic acid and elaidic acid grown bacteria were able to repair DNA strand breaks to the same extent. When irradiation was in nutrient conditions both bacteria at all temperatures of irradiation repaired DNA strand breaks equally well and to a greater extent than in non-nutrient suspension.