A critical appraisal of the association between energy charge and cell damage

The effects of a novel herbal toothpaste on salivary lactate dehydrogenase as a measure of cellular integrity

OBJECTIVE

Lactate dehydrogenase (LDH) is a critical intracellular enzyme responsible for anaerobic respiration in pyruvate metabolism which becomes detectable in extracellular spaces after cellular breakdown. This clinical investigation examined the effects of brushing with a test toothpaste containing natural ingredients, i.e., clove (Syzygium aromaticum), aloe vera (Aloe barbadensis), amla (Emblica officinalis), neem (Azadirachta indica), tulsi (Ocimum basillicum), and honey (from Apis mellifera), and 0.96% zinc (zinc oxide, zinc citrate) and 0.76% SMFP (1000 ppm F) in a calcium carbonate base formulated with natural ingredients (Ved Shakti, Colgate Palmolive India) and a fluoride toothpaste containing 0.76% SMFP (1000 ppm F) in a calcium carbonate base (Colgate Cavity Protection, Colgate Palmolive; henceforth control) on salivary LDH in conjunction with the assessments of dental plaque and gingivitis representing oral hygiene parameters.

MATERIALS AND METHODS

This double-blind, two-cell study enrolled 70 adults (age range 20-59 years). Subjects completed a washout and provided baseline saliva samples for LDH analysis and clinical assessments of dental plaque and gingivitis using the Turesky Modification of Quigley-Hein and Loe-Silness methods respectively. Subjects were randomly assigned to brush their teeth with either the test or control. Post-treatment sample collection and clinical evaluations were conducted after 3 weeks, 6 weeks, and 12 week sof brushing with all assessments conducted 12 h after hygiene. Statistical analyses were conducted independently for each parameter by t-test for within treatment evaluation and analysis of covariance (ANCOVA) for between treatment comparisons.

RESULTS

At baseline, treatment groups demonstrated no significant differences for LDH or dental plaque and gingival index scores. Brushing with the test demonstrated progressive reductions in salivary LDH, plaque and gingival index scores over the study duration in comparison to the control. The test demonstrated reductions in LDH of 9.5-15.4% over the study period in comparison to the control representing statistically significant effects (p < 0.05). The test also demonstrated reductions in dental plaque that ranged between 6.4 and 16.2% over the study period and gingivitis reductions that ranged between 8.2 and 23.8% representing statistically significant results (p < 0.05).

CONCLUSIONS

Brushing with a novel herbal toothpaste demonstrated significant reductions in salivary LDH representing improvements in cellular integrity with concurrent reductions in dental plaque and gingivitis as compared to the control dentifrice.

CLINICAL RELEVANCE

Salivary LDH measurements offer a non-invasive and objective measurement of mucosal cellular integrity complementing other evaluations and clinical assessments such as plaque and gingival index scores.

Pathophysiological amyloid concentrations induce sustained upregulation of readthrough acetylcholinesterase mediating anti-apoptotic effects

Cholinergically differentiated SH-SY5Y neuroblastoma cells were treated with a pathophysiologically relevant, low (300 nM), and a high (3 μM) dose of amyloid beta 1-42 (Abeta) or 42-1 (revAbeta). At early (1 and 4h) and late (24h) time points, the pro- and anti-apoptotic factors--caspase-3 and p53, and B-cell lymphoma 2 protein (Bcl-2), respectively--were assessed together with lactate dehydrogenase (LDH) release as measure of cell viability and ATP levels as marker of mitochondrial activity. The low peptide dose significantly increased Bcl-2 and, time-delayed, caspase-3 and ATP levels, but barely impacted on LDH release, while the high concentration remarkably depressed Bcl-2 levels, depleted ATP and led to increased LDH release. We also monitored acetylcholinesterase (AChE) enzymatic activity and splice variant levels (tailed and readthrough AChE; AChE-T and AChE-R), and assessed choline acetyltransferase (ChAT) and high-affinity choline uptake (HACU). The low Abeta concentration drastically upregulated AChE-R and increased both ChAT and HACU, while the high dose caused cholinergic toxicity. We believe this study offers the first insight into the highly concentration-dependent effects of Abeta on cholinergic dynamics. In particular, it highlights the rescuing role of AChE-R as being, together with mitochondrial activity, involved in cholinergic adaptation to low doses of Abeta.

Mitochondrial dysfunction induced by sertraline, an antidepressant agent

Sertraline, a selective serotonin reuptake inhibitor, has been used for the treatment of depression. Although it is generally considered safe, cases of sertraline-associated liver injury have been documented; however, the possible mechanism of sertraline-associated hepatotoxicity is entirely unknown. Here, we report that mitochondrial impairment may play an important role in liver injury induced by sertraline. In mitochondria isolated from rat liver, sertraline uncoupled mitochondrial oxidative phosphorylation and inhibited the activities of oxidative phosphorylation complexes I and V. Additionally, sertraline induced Ca(2+)-mediated mitochondrial permeability transition (MPT), and the induction was prevented by bongkrekic acid (BA), a specific MPT inhibitor targeting adenine nucleotide translocator (ANT), implying that the MPT induction is mediated by ANT. In freshly isolated rat primary hepatocytes, sertraline rapidly depleted cellular adenosine triphosphate (ATP) and subsequently induced lactate dehydrogenase leakage; both were attenuated by BA. Our results, including ATP depletion, induction of MPT, inhibition of mitochondrial respiration complexes, and uncoupling oxidative phosphorylation, indicate that sertraline-associated liver toxicity is possibly via mitochondrial dysfunction.

Mitochondrial mass is inversely correlated to complete lipid oxidation in human myotubes

Exercise increases while physical inactivity decrease mitochondrial content and oxidative capacity of skeletal muscles in vivo. It is unknown whether mitochondrial mass and substrate oxidation are related in non-contracting skeletal muscle. Mitochondrial mass, ATP, ADP, AMP, glucose and lipid oxidation (complete and incomplete) were determined in non-contracting myotubes established from 10 lean, 10 obese and 10 subjects with type 2 diabetes precultured under normophysiological conditions. ATP, ADP, AMP, mitochondrial mass and energy charge were not different between groups. In diabetic myotubes, basal glucose oxidation and incomplete lipid oxidation were significantly increased while complete lipid oxidation was lower. Mitochondrial mass was not correlated to glucose oxidation or incomplete lipid oxidation in human myotubes but inversely correlated to complete lipid oxidation. Thus within a stable energetic background, an increased mitochondrial mass in human myotubes was not positive correlated to an increased substrate oxidation as expected from skeletal muscles in vivo but surprisingly with a reduced complete lipid oxidation.

Intracellular adenosine triphosphate delivery enhanced skin wound healing in rabbits

Small unilamellar lipid vesicles were used to encapsulate adenosine triphosphate (ATP-vesicles) for intracellular energy delivery. This technique was tested in full-thickness skin wounds in 16 adult rabbits. One ear was rendered ischemic by using a minimally invasive surgery. The other ear served as a normal control. Four circular full-thickness wounds were created on the ventral side of each ear. ATP-vesicles or saline was used and the wounds were covered with Tegaderm (3M, St. Paul, MN). Dressing was changed and digital photos were taken daily until all the wounds were healed. The mean healing times of ATP-vesicles-treated wounds were significantly shorter than that of saline-treated wounds on ischemic and nonischemic ears. Histologic study indicated better-developed granular tissue and reepithelialization in the ATP-vesicles-treated wounds. The wounds treated by ATP-vesicles exhibited extremely fast granular tissue growth. More CD31 positive cells were seen in the ATP-vesicles-treated wounds. This preliminary study shows that direct intracellular delivery of ATP can accelerate the healing process of skin wounds on ischemic and nonischemic rabbit ears. The extremely fast granular tissue growth was something never seen or reported in the past.

Enhancing skin wound healing by direct delivery of intracellular adenosine triphosphate

BACKGROUND

A new intracellular adenosine triphosphate (ATP) delivery technique has been developed and was tested for skin wound care.

METHODS

Eleven pairs of adult nude mice were used. ATP-vesicles were applied in 11 mice, and another 11 mice were treated with lipid vesicles only.

RESULTS

The group treated with ATP-encapsulated fusogenic small, unilamellar lipid vesicles healed faster than the group treated with only lipid vesicles. Histologic study indicated better developed granular tissue and re-epithelialization in the study group, and wound tissue vascular endothelial growth factor expressions were also higher in ATP-vesicles treated mice.

CONCLUSIONS

This intracellular ATP delivery system may provide a new hope for wound healing as well as the treatment of medical conditions in which ischemia is involved.

Paradoxical Toxicity of Cardioplegic Compounds on Ischemic Cardiomyocyte Using Optimal Design Strategy

BACKGROUND

The aim of this study was to evaluate the effects of major components of cardioplegic solutions on myocardial tissue submitted to prolonged cold ischemia.

METHODS

Our methodology was based on the simultaneous testing in the same series of experiments of many compounds (19 in number), which were included in the composition of 20 established solutions. All the experiments were performed by a matricial-predefined protocol that allows the evaluation of the protective or toxic effects of each of these 19 compounds. Pig hearts were removed and left ventricular myocardiums were cut into 320 pieces. For each solution tested, 8 pieces of myocardial tissue were incubated at 4 degrees C for 24 hours and 8 other pieces were incubated for 72 hours. At the end of incubation period, tissue injury was assessed by measuring the leakage of myocardial enzymes(glutamic-oxaloacetic transaminase, lactate dehydrogenase, creatine phosphokinase) into the incubation medium. Initially, the effects of each solution were evaluated, and then a mathematical analysis was performed and the effects of each compound deduced.

RESULTS

After the 24-hour incubation period, pyruvate (5 mmol/liter), polyethylene glycol (5 mmol/liter), Ala-Gln (20 mmol/liter), and reduced glutathione (3 mmol/liter) showed toxic effects, whereas ethanol (1%) and calcium chloride (2 mmol/liter) seemed to be protective. After 72 hours' incubation, similar data were obtained; dextran 70 (0.57 mmol/liter) was also found to be deleterious.

CONCLUSIONS

The results revealed surprising myocardial toxicity (enzymatic release) from components included in cardioplegic solutions. Some components would induce metabolic activation during prolonged hypothermic ischemia, which may be inappropriated and which may perhaps exacerbate damages by increasing membrane ruptures. This concept confirms eventual discrepant effects of preservative compounds on cardiomyocyte membrane during deep hypothermia, according to the metabolic state of the cell.

Laboratory markers and germ cell tumors

The International Germ Cell Consensus Classification (IGCCC) of testicular germ cell tumors (TGCT) in 1997 included three serum tumor markers, serum lactate dehydrogenase catalytic concentration (S-LD), serum alpha fetoprotein concentration (S-AFP), and serum human chorionic gonadotropin concentration (S-hCG). The recommendation should be implemented for all patients with TGCT and is also useful for patients with ovarian and extragonadal germ cell tumors. A fourth serum tumor marker for TGCT, S-LD isoenzyme 1 (S-LD-1), is also relevant for TGCT. Patients with seminoma have a raised S-LD-1 more often than a raised S-AFP and S-hCG, whereas patients with nonseminoma have a raised S-AFP more often than a raised S-LD-1 and S-hCG. A new model combining IGCCC and S-LD-1 predicts survival better than previous staging systems. LD-1 is related to a characteristic chromosomal abnormality in all types of TGCT, a high copy number of chromosome 12p. In contrast, AFP and hCG are found mainly in nonseminomatous germ cell tumors and they related to the histologic differentiation of the tumors. The different biologic background for the serum tumor markers may contribute to the difference in their clinical behavior.

Using fructose-1,6-diphosphate during hypothermic rabbit-heart preservation: a high-energy phosphate study

BACKGROUND

In this study, we evaluated the effects of fructose-1,6-diphosphate (FDP) on high-energy phosphate metabolism during 18-hour hypothermic rabbit-heart preservation.

METHODS

Under general anesthesia and artificial ventilation, hearts from 42 adult New Zealand white rabbits were harvested, flushed, and preserved in St. Thomas solution at 4(o)C for 18 hours. In the study group (n = 15), FDP (5 mmol/liter) was added to the St. Thomas solution, whereas in the control group (n = 17), fructose (5 mmol/liter) was added. Another 10 hearts did not undergo hypothermic storage, but were used as the normal group for high-energy phosphate concentration comparison.

RESULTS

After 18 hours of hypothermic preservation, myocardial high-energy phosphate content decreased in both preservation groups. In the study group, left ventricular adenosine triphosphate (ATP) content was 33% of that in the normal hearts, but in the control group, ATP decreased to 14% of normal. Adenosine diphosphate (ADP) content, energy charge, and ATP-to-ADP ratio showed similar decreases. The high-energy phosphate profile (content in the atria and ventricles and the ratio of ATP to ADP to AMP) was maintained in the study group but not in the control group. High-energy phosphate metabolites such as inosine monophosphate (IMP), inosine, and hypoxanthine increased in both preservation groups, but the increase was more prominent in the control group.

CONCLUSION

Adding FDP to St. Thomas solution attenuated the depletion of high-energy phosphate concentration in the preserved hearts. This difference was especially prominent in the left and right ventricles. The protective effect of FDP during hypothermic heart preservation deserves further study.

Effect of tributyltin on adenylate content and enzyme activities of teleost sperm: a biochemical approach to study the mechanisms of toxicant reduced spermatozoa motility

The effects of tributyltin (TBT) on the energy metabolism and motility of fish spermatozoa were investigated in vitro in African catfish and common carp. A significant (P<0.05) decrease of the duration and the intensity of motility was observed in catfish spermatozoa exposed to 0.27 microg/l TBT for 24 h. Exposure of catfish spermatozoa to 2.7-27 microg/l TBT caused an instant decrease in ATP content. In the presence of 27 microg/l TBT approximately 55% of the initial ATP concentration in catfish semen was lost after 60 min incubation while AMP concentrations increased and the total adenine nucleotide (TAN) pool remained unchanged. The reduction in sperm ATP levels could not be attributed to cell death since viability decreased only slightly over the period of exposure. In carp by contrast, none of the adenylates concentrations studied (ATP, ADP and AMP) were affected by TBT exposure at any experimental condition. However, carp sperm motility was significantly reduced by exposure to 2.7 microg/l TBT. Among the enzymes investigated only lactate dehydrogenase (LDH) in catfish sperm was significantly (P<0.01) affected by 27 microg/l TBT treatment with a reduction in activity of approximately 75%. Compared with carp sperm before TBT exposure, that of catfish had lower adenylate contents and overall lower enzymatic activities; this explains its slower sperm velocity and shorter duration of movement as measured by computer assisted sperm analysis (CASA). The present in vitro study shows that catfish spermatozoa are more sensitive to TBT exposure (and probably to other toxicants) than those of carp.

Intestinal energy metabolism during ischemia and reperfusion

BACKGROUND

In order to evaluate acute ischemic damage in the small intestine induced by superior mesenteric artery occlusion (SMAO) and subsequent reperfusion, changes in ATP, ADP, and AMP were measured by high-performance liquid chromatography, and changes in tissue blood flow were measured (from the serosal surface) by the laser doppler flow meter in a rat model.

MATERIALS AND METHODS

The superior mesenteric artery of the rat was occluded for 30, 60, 90, and 120 min and then reopened. Core temperature was maintained carefully at 37 +/- 0.3 degrees C.

RESULTS

All rats that underwent 90 and 120 min of SMAO died within 2 days, but those with 30 and 60 min of SMAO survived. ATP (10.39 +/- 0.90 micromol/g dry weight), ADP (3.34 +/- 0.33), and total adenine nucleotides (TAN; 14.08 +/- 0. 86) decreased with longer SMAO times. After 30 and 60 min of SMAO followed by reperfusion, recoveries of ATP and TAN were relatively good and ADP levels remained fairly steady, but little or no recovery of these levels was observed after 90 and 120 min of SMAO followed by reperfusion. There were linear correlations between the levels of ATP and TAN after 30 min of reperfusion and the time of SMAO. Tissue blood flow levels were constant during SMAO. After reperfusion, those levels were recovered along with the SMAO periods. But recovery rates compared with control values were not related with those of ATP. CONCLUSIONs. ATP and TAN levels, particularly at 30 min after reperfusion, seemed to be in good agreement with the tissue damage and the viability of the small intestine. We propose that the measurement of these levels may be useful for the evaluation of intestinal damage and viability.

Heat response of HT29 cells depends strongly on perfusion--a 31P NMR spectroscopy, HPLC and cell survival analysis

A model system of perfused human colon adenocarcinoma cells (HT29) encapsulated in alginate was used to examine metabolic response to heat therapy with 31P NMR spectroscopy, HPLC and cell survival analysis. The presented data show, that perfused (medium flow during hyperthermia) and non-perfused (no medium flow during hyperthermia) cells are very difficult in their sensitivity to hyperthermia. Under equivalent experimental conditions with respect to medium pH, oxygen and nutrient concentration, encapsulated perfused HT 29 cells display a significantly lower thermal sensitivity than non-perfused cells. This reduced sensitivity of perfused cells is characterized by an increased cell survival and relative ATP concentration, and reduced drop of the NTP/Pi ratio in the long-term follow up towards zero. The relative ATP concentration determined by HPLC after hyperthermia is correlated with the clonogenic survival fraction. There is a direct relationship, depending on the specific experimental conditions (perfused, non-perfused). For perfused cells only a slight dependency of survival and relative ATP concentration on heat dose is observed. In consequence, the correlation between survival and relative ATP concentration is weak, described by log(SFperf) = 0.7*[ATP-12.4, R2 = 0.79, p < 0.04. For non-perfused cells the correlation is stronger resulting in a relationship of log(SFno perf) = 0.6*[ATP]-9.0, R2 = 0.98, p < 0.0002. Altogether, the presented data suggest that the relative ATP concentration measured by HPLC after hyperthermia might be predictive for cell survival. On the other hand, a dependence between cell survival and long-term changes of NTP/Pi has been found. The results confirm the importance of tumour perfusion for hyperthermia-induced metabolic changes and cytotoxicity and therefore, for the therapeutic outcome.

Effect of nickel-based dental casting alloys on fibroblast metabolism and ultrastructural organization

Previous cell culture evaluations have shown that nickel-chromium dental alloys did not affect cellular viability or morphology. However, nickel-based alloys released corrosion products which decreased cellular proliferation. It was hypothesized that this decrease was due to an interference of cellular energy metabolism by released metal ions. To test this hypothesis, we evaluated the effects on cellular energy metabolism, adenosine triphosphate (ATP) levels, and cellular ultrastructure by four nickel-based alloys, including high and low chromium alloys with and without beryllium additions, in human gingival fibroblast cell cultures. Energy metabolism was evaluated by measuring glucose-6-phosphate dehydrogenase (G-6-PDH) activity. ATP levels were measured with the luciferin-luciferase method. Cellular membranes and ultrastructural organization were evaluated by scanning and transmission electron microscopy. The results of this study showed that metal ions released from all alloys completely inhibited G-6-PDH activity and reduced cellular ATP levels as compared to controls. The reduction in intracellular ATP was greater for the beryllium containing alloys than the non-beryllium-containing alloys. However, no morphologic changes in cellular membranes or organelles were observed. These results support the hypothesis that metal ions released from nickel-based dental casting alloys interfere with cellular energy metabolism.

Importance of various types of metabolic inhibition for cell damage caused by direct membrane damage

Cell damage is caused by energy depletion or by direct membrane damage, or a combination when a direct membrane damage affects energy depleted cells. In this report it was investigated whether the extent of direct membrane damage induced by lysophosphatidyl choline (LPC) or phospholipase C (PhC) on quiescent fibroblasts depended on the metabolic state of the cells. When glycolysis was inhibited cell damage was always extensively increased, whereas cell damage was also increased to a minor degree when exposed to PhC during sole inhibition of oxidative phosphorylation. Acceleration of glycolysis in cells with a low rate of glycolysis resulted in a dramatic improvement of the membrane susceptibility within a few minutes. Thus, susceptibility of the cell membrane to direct membrane damage depends on the metabolic state. The results also emphasize previous findings that glycolysis has a special role in maintaining membrane function and integrity.

Biochemical mechanism of irreversible cell injury caused by free radical-initiated reactions

Effects of oxidative stress on isolated rat ventricular myocytes were studied. Myocyte viability was determined by the ability of these cells to retain rod-shaped morphology and to exclude trypan blue. The mean life time of myocytes was quantitated using the Weibull distribution function. Superfusion with 200 microM tert-butyl hydroperoxide (t-BHP) led to a time-dependent loss of cell viability, generation of the products of lipid peroxidation, oxidation of protein and non-protein thiols, a decrease in [ATP]i and in the cellular energy charge. Dithiothreitol (DTT, 5 mM) prolonged survival of myocytes exposed to t-BHP, attenuated oxidation of protein and non-protein thiols, and preserved the energy charge. Exposure to DTT did not affect the concentration of t-BHP-generated lipid peroxidation products. Promethazine (1 microM) prevented t-BHP-induced increase in the concentration of lipid peroxidation products, but did not prevent either loss of thiols or loss of cell viability. Superfusion with N-ethylmaleimide (NEM, 5 microM) also led to loss of cell viability, with accompanying decreases in protein and non-protein thiols, ATP and energy charge without the accumulation of the products of lipid peroxidation. Superfusion with FeSO4 (400 microM) and ascorbate (1 mM), (Fe-Asc) did not result in loss of cell viability or a decrease protein thiols or the energy charge. Superfusion with Fe-Asc, did, however, lead to a slight decrease in the concentration of non-protein thiols and ATP and a large increase in the concentration of lipid peroxidation products. Accumulation of lipid peroxidation products induced by Fe-Asc was prevented by promethazine.(ABSTRACT TRUNCATED AT 250 WORDS)

Eugenol triggers different pathobiological effects on human oral mucosal fibroblasts

Pathobiological effects of eugenol (4-allyl-2-methoxyphenol), a major constituent of betel quid (BQ), were studied on oral mucosal fibroblasts. At a concentration higher than 3 mmol/L, eugenol was cytotoxic to oral mucosal fibroblasts in a concentration- and time-dependent manner. Cell death was associated with intracellular depletion of glutathione (GSH). Most of the GSH was depleted prior to the onset of cell death. At concentrations of 3 mmol/L and 4 mmol/L, eugenol depleted about 45% and 77% of GSH after one-hour incubation. In addition, eugenol decreased cellular ATP level in a concentration- and time-dependent manner. Eugenol also inhibited lipid peroxidation. Inhibition of lipid peroxidation was partially explained by its dose-dependent inhibition of xanthine oxidase activity. The IC50 of eugenol on xanthine oxidase activity was about 0.3 mmol/L. No DNA strand break activity for eugenol was found at concentrations between 0.5 and 3 mmol/L. Taken together, frequent exposure of oral mucosa to a high concentration of eugenol during the chewing of BQ might be involved in the pathogenesis of oral submucous fibrosis and oral cancer via its cytotoxicity. In contrast, eugenol at a concentration less than 1 mmol/L might protect cells from the genetic attack of reactive oxygen species via inhibition of xanthine oxidase activity and lipid peroxidation.

Removal of calcium overload caused by A23187 is more dependent on glycolysis than oxidative phosphorylation

An increase of cytosol Ca2+ may be the mediator of irreversible cell damage after ATP depletion. Ca2+ influx can also be induced by addition of the ionophore A23187. The extent of cell damage caused by A23187 during concomitant metabolic inhibition was investigated on quiescent fibroblasts. Inhibition of glycolysis resulted in increased cell damage compared to control, whereas an increased rate of glycolysis during inhibition of oxidative phosphorylation attenuated cell damage. These results indicate that glycolysis plays an important part in the removal of entering Ca2+.

Alterations in mitochondrial function and morphology in chronic liver disease: pathogenesis and potential for therapeutic intervention

Studies assessing mitochondrial function and structure in livers from humans or experimental animals with chronic liver disease, including liver cirrhosis, revealed a variety of alterations in comparison with normal subjects or control animals. Depending on the etiology of chronic liver disease, the function of the electron transport chain and/or ATP synthesis was found to be impaired, leading to decreased oxidative metabolism of various substrates and to impaired recovery of the hepatic energy state after a metabolic insult. Changes in mitochondrial structure include megamitochondria with reduced cristae, dilatation of mitochondrial cristae and crystalloid inclusions in the mitochondrial matrix. The most important strategies to maintain an adequate mitochondrial function per liver are mitochondrial proliferation and increases in the activity of critical enzymes or in the content of cofactors per mitochondrion. Possibilities to assess hepatic mitochondrial function and to treat mitochondrial dysfunction in patients with chronic liver disease are discussed.

Microregional distributions of glucose, lactate, ATP and tissue pH in experimental tumours upon local hyperthermia and/or hyperglycaemia

Microregional distributions of glucose, lactate and ATP concentrations as well as tissue pH values were determined in subcutaneous rat tumours during normothermia and normoglycaemia, and upon local hyperthermia (HT) and/or hyperglycaemia (HG). Experiments were performed in order to investigate whether, and to what extent, these adjuvant therapeutic measures applied alone or in combination can modify the bioenergetic and metabolic status, parameters that are known to markedly influence the therapeutic response of tumours to heat. Local HT was performed in a saline bath (44 degrees C/2 h) and HG was induced by i.v. infusion of glucose for 2.5 h (blood glucose levels during heating: 35-40 mM). Immediately after treatment, the microregional distributions of glucose, lactate and ATP concentrations were assessed using quantitative bioluminescence and single-photon counting. In corresponding histological sections the fraction of tumour tissue with changes indicating cellular damage was determined. For comparison, global levels of glucose, lactate, ATP, ADP and AMP were measured using enzymatic assays or HPLC. Tumour tissue pH values were recorded immediately after treatment with miniaturised needle glass pH electrodes. Upon HT alone, the microregional glucose distribution remained unchanged. Lactate concentrations significantly increased, resulting in a pH drop of about 0.20 pH units. Mean ATP concentrations decreased without an obvious change in the shape of the distribution curve. The fraction of tumour tissue showing cellular damage increased from 18% (in control tumours) to 27%. Upon HG alone, mean glucose and lactate levels in the tumours increased. Glucose, lactate and pH distributions became broader. Lactate accumulation results in a severe tumour acidosis (mean pH = 6.22). Mean ATP concentrations marginally decreased despite a higher glucose availability, probably because of poorer ATP yield resulting from changes in metabolic channelling (Crabtree effect). The fraction of tumour tissue exhibiting cellular damage was 23%. Following the combined treatment (HT/HG), glucose and lactate levels, and tissue pH were similar to those seen upon HG alone. However, ATP concentrations were lowest under this condition. The variation of tumour ATP concentrations is substantially reduced with only a few tumour areas remaining with ATP levels of at least 0.6 mumol/g. The ATP depletion upon HT/HG is accompanied by a drastic increase in the fraction of tissue areas exhibiting cellular damage to 61%. It may therefore be concluded that only the combined treatment can deplete ATP to such an extent that a pronounced cytotoxic effect is achieved.

Geographical mapping of metabolites in biological tissue with quantitative bioluminescence and single photon imaging

This article features a novel technique for measuring the spatial distribution of metabolites, such as ATP, glucose, and lactate, in rapidly frozen tissue. Concentration values are obtained in absolute terms and with a spatial resolution of single-cell dimension. The method is based on enzymatic reactions that link the metabolite of interest to luciferase with subsequent light emission. Using a specific array, cryosections are brought into contact with the enzymes in a well-defined, reproducible way inducing a distribution of light across the section with an intensity that is proportional to the metabolite concentration. The emitted light can be visualized through a microscope and an imaging photon counting system, and the respective image can be transferred to a computer for image analysis. Measurements in spherical cell aggregates with central necrosis demonstrate a close correlation between the distribution of ATP and of cellular viability at a microregional level. Similarly, ATP and glucose are correlated with the geometrical arrangement of more viable and more necrotic tissue regions in human melanomas xenografted in nude mice. Lactate did not show such a structure-related distribution in these tumours. Structure-related distributions of ATP, glucose, and lactate are found in cervix tumours of patients. In contrast to the heterogeneous distributions in tumours, the distribution patterns were much more homogeneous in normal tissues. Regional differences were present, but were much more gradual than in malignancies. This was illustrated for heart muscle where ATP concentrations were found that agreed with data in the literature, and that showed a decrease in periventricular areas.

Effect of oxidant stress on calcium signaling in vascular endothelial cells

The endothelial cell is recognized as a critical modulator of blood vessel tone and reactivity. This regulatory function of endothelial cells occurs via synthesis and release of diffusible paracrine substances which induce contraction or relaxation of adjacent vascular smooth muscle. In response to stimulation by blood-borne agonists such as bradykinin or histamine, the endothelial cell utilizes cytosolic ionic Ca2+ as a trigger in the transduction of the stimulatory signal into a paracrine response. Considerable evidence has accumulated to indicate that various forms of biologically important oxidant stress alter vascular function in an endothelium-dependent manner. Further, oxidant stress is known to alter the mechanisms which govern Ca2+ homeostasis in the endothelial cell. Recently, we have described a model in which the oxidant tert-butylhydroperoxide is utilized to examine the effects of oxidant stress on Ca(2+)-dependent signal transduction in vascular endothelial cells. In this model, three temporal phases are evident and consist of (1) inhibition of the agonist-stimulated Ca2+ influx pathway, (2) inhibition of receptor-activated release of Ca2+ from internal stores and elevation of resting cytosolic free Ca2+ concentration, and (3) progressive increase in resting cytosolic Ca2+ concentration and loss of responsiveness to agonist stimulation. In this review, the mechanisms which characterize agonist-stimulated Ca2+ signaling in vascular endothelial cells, and the effects of oxidant stress on signal transduction will be described. The mechanisms potentially responsible for oxidant-induced inhibition of Ca2+ signaling will be considered.

Pixel-to-pixel correlation between images of absolute ATP concentrations and blood flow in tumours

Iodo(14C-)antipyrine autoradiography and imaging bioluminescence have been combined to obtain pixel-to-pixel correlations between absolute values for local blood flow and ATP concentrations at a microscopical level within designated areas in hamster melanomas. Positive pixel-to-pixel correlations were obtained in 4 of 6 tumours. Both flow and ATP values were less in mostly necrotic than in mostly viable tumour regions. The data provide evidence for the energetic state of cancer cells being strongly influenced by the efficiency of tumour microcirculation in several but not in all malignancies investigated.

Adenosine A1 receptor activation attenuates cardiac injury produced by hydrogen peroxide

Adenosine has been shown to protect the ischemic and reperfused myocardium. To examine whether the protective effect of the nucleoside is mediated by modulation of oxidative stress, isolated rat hearts were perfused for 30 minutes with 100 microM H2O2 or an exogenous free radical-generating system consisting of purine (3.06 mM) and xanthine oxidase (10 units/l) in the presence or absence of drugs acting on adenosine A1 or A2 receptors. H2O2 alone produced a greater than 90% loss in contractility concomitant with a threefold elevation in resting tension, although these effects occurred in the absence of ultrastructural damage. Two A1 receptor agonists N6-cyclopentyladenosine (CPA, 1 microM) and R(-)-N6-(2-phenylisopropyl)adenosine (R-PIA, 1 microM) significantly attenuated the cardiodepressant effects of H2O2 and depressed the elevation in resting tension; however, only the effect of CPA was found to be significant with regard to the latter parameter. A similar concentration of S(+)-N6-(2-phenylisopropyl)adenosine (S-PIA), a markedly less potent A1 receptor agonist, was found to be without beneficial effect. However, a significant protective effect against both the reduction in contractility and the elevation in resting tension was seen with a 10-fold elevation in the concentration of S-PIA (10 microM). The protective effects on functional parameters were associated with preservation of high-energy phosphate and adenine nucleotide contents after 30 minutes of H2O2 treatment. The salutary effects of all drugs were reversed in the presence of the A1 receptor antagonist 1,3-dipropyl-8-cyclopentylxanthine (0.5 microM). An A2 receptor agonist 2-[p-(carboxyethyl)phenethylamino]-5'-N-ethylcarboxamidoadenosine, termed CGS 21680 (1 microM), failed to alter the cardiac response to H2O2 with regard to all parameters studied. Neither a 50% reduction in external CaCl2 concentration nor treatment with 10 microM DL-propranolol exerted salutary effects against H2O2-induced dysfunction. None of the A1 receptor agonists modulated the response to purine plus xanthine oxidase. Our results demonstrate a selective protective effect of adenosine A1 receptor activation against the cardiac toxicity of H2O2 and provide, at least in part, a basis for the cardioprotective actions of adenosine and its analogues.

Adaptation of mitochondrial metabolism in liver cirrhosis. Different strategies to maintain a vital function

Mitochondrial function and structure in cirrhotic livers from humans or rats show a variety of changes as compared to control livers. Mitochondrial ATP production is reduced in rats with CCl4- or thioacetamide-induced liver cirrhosis and in rats with secondary biliary cirrhosis. Activity of the electron transport chain is decreased in rats with secondary biliary cirrhosis. In rats with CCl4-induced cirrhosis, the mitochondrial content of certain constituents of the respiratory chain (cytochrome a + a3, cytochrome b and ubiquinone) is increased and activities of cytochrome c oxidase and ATPase are elevated. Similarly, in humans with liver cirrhosis, mitochondrial cytochrome a + a3 content is elevated and has been used to assess the risk for hepatectomy. In rats with secondary biliary cirrhosis, compensatory strategies include increased mitochondrial volume per hepatocyte and possibly increased extramitochondrial ATP production (increased glycolysis). Thus, a variety of adaptive mechanisms are used to maintain mitochondrial function in cirrhotic livers.

Nucleotide and nucleic acid metabolism in rat thymocytes during cell cycle progression

A complete cell cycle of mature, concanavalin A (Con A) stimulated rat thymocytes was documented by analyzing the cell number as well as the content and synthesis of DNA and RNA. Cell cycle progression is accompanied by an elevation of class I, II and III RNA polymerase activities (about 10-fold) in the S phase maximum, 48 h after stimulation. Moreover, maximal cellular contents of DNA, ATP, ADP and AMP were observed at this culture period, whereas the RNA level peaked at 60 h. The synthesis of purine and pyrimidine nucleotides de novo was detected by use of [14C]HCO3-. Maximal incorporation rates of [14C]HCO3- into nucleotides (de novo synthesis) and of [3H]adenine into adenylates ('salvage pathway') occur during the S phase. However, the de novo synthesis rates were markedly lower than those of the 'salvage pathway'. The highest cellular level of the nucleotide precursor 5-phosphoribosyl-1-pyrophosphate (8.4-fold increase) also coincided with the S phase.

Calcium-dependent opening of a non-specific pore in the mitochondrial inner membrane is inhibited at pH values below 7. Implications for the protective effect of low pH against chemical and hypoxic cell damage

1. The rate of opening of the Ca(2+)-induced non-specific, cyclosporin A-inhibited, pore of the mitochondrial inner membrane of rat heart and liver mitochondria at pH 6.0 was less than 10% of that at pH 7.4. 2. The effect could not be explained by inhibition of Ca2+ uptake into the mitochondria, or of the matrix peptidyl-prolyl cis-trans isomerase (PPIase), or of the Ca(2+)-induced conformational change of the adenine nucleotide translocase. 3. It is suggested that the proposed interaction of matrix PPIase with the 'c' conformation of the adenine nucleotide carrier in the presence of Ca2+ [Griffiths & Halestrap (1991) Biochem. J. 274, 611-614] is inhibited by low pH. 4. The relevance of this to the protective effect of low pH on hypoxic and chemical-induced cell damage is discussed.

Comparative imaging of structure and metabolites in tumours

A novel technique for metabolic imaging using quantitative bioluminescence and single photon imaging was used to measure the distribution of ATP and lactate in two types of human melanoma xenografts with different radiobiologically hypoxic cell fractions (MF: 45 +/- 17% and EE: 6 +/- 3%; mean +/- SD). The tumours were s.c. grown in nude mice and were used for measurement at volumes of 153-3072 mm3. For metabolic imaging the rapidly frozen tumours were serially sectioned, and each cryosection was brought into contact with a frozen bioluminescent enzyme cocktail using a specially designed glass sandwich system. After thawing section and cocktail the luminescence was started, and light was emitted from the section with an intensity that is proportional to the local metabolite concentration. The photons were imaged directly through a microscope and an imaging photon counting system. A clear-cut correlation was documented between the distribution of relatively high ATP concentrations and of viable cell regions. The data obtained showed lower ATP concentrations in the tumour centres compared to the periphery, whereas lactate was inversely distributed within the melanomas. There was a trend towards a decrease in ATP with increasing tumour size in central, but not in peripheral, parts of both melanoma types. The concentration of neither ATP nor lactate measured in corresponding tumour areas showed differences related to the melanoma type. Thus, these two metabolites did not reflect the difference in the radiosensitivity of these tumours.

Cell damage caused by ATP depletion is reduced by magnesium and nickel in human fibroblasts--a non-specific calcium antagonism?

Calcium has been suggested to be the final common mediator of cell damage, but conflicting reports to prove this hypothesis have appeared. In order to elucidate the role of calcium in cell damage caused by ATP depletion, the effect of addition of calcium channel blockers (verapamil and nitrendipine) and non-specific antagonists (magnesium and nickel) was investigated in a model system of quiescent fibroblasts. ATP depletion was induced by metabolic inhibitors and the cell damage was assessed by the release of lactate dehydrogenase. Verapamil and nitrendipine did not protect the cells during ATP depletion, whereas a high concentration of Mg2+ (3-10 mmol/l) or a lower concentration of Ni2+ (0.5-1.0 mmol/l) reduced the cell damage considerably. An increased extracellular concentration of Ca2+ resulted in augmented cell damage. The effect of Mg2+ and Ni2+ was not due to an interference with the metabolic inhibitors or a reduction of the energy consumption. Both Ni2+ and Mg2+ were able to counteract the cell damage induced by entrance of Ca2+ after addition of the ionophore A23187. However, Mg2+ and Ni2+ were deleterious for the cells during ATP regeneration after an initial ATP decrease. These results indicate that a non-specific antagonism of Ca2+ may reduce cell damage, and, therefore, that Ca2+ may have an important role in cell damage, but also that a non-specific antagonism of Ca2+ during regeneration of ATP depleted cells is deleterious.

Ischemic brain injury in vitro: protective effects of NMDA receptor antagonists and calmidazolium

Excessive Ca2+ influx through NMDA receptor-coupled channels has been linked to neuronal cell death. Using an in vitro model of transient brain ischemia, we investigated possible protective effects of NMDA receptor antagonists ketamine or MK-801 and of calmidazolium, an inhibitor of intracellular Ca2(+)-activated proteins. Brain ischemia/recovery was simulated in isolated hippocampal slices and injury monitored by measurement of ATP levels. Omission of both glucose and oxygen (but not oxygen alone) for 20 min led to persistent ATP deficits after 4 h recovery. Addition of ketamine or MK-801 at 1 microM permitted ATP to recover within 1 h, as did addition of calmidazolium at 10 microM. Our findings are consistent with other reports that NMDA receptor antagonists can protect neuronal tissue from ischemic damage. The role of inappropriately activated Ca2(+)-mediated signaling processes in the mechanism(s) of such injury is suggested by the protection also seen with calmidazolium, an inhibitor of calmodulin and other structurally related proteins such as calpain(s) and protein kinase C. The inhibition of intracellular Ca2+ target proteins may be an alternative for protection of the brain against injury due to insults that activate NMDA receptors.