Pulmonary alveolar macrophage. Oxidative metabolism of isolated cells and mitochondria and effect of cadmium ion on electron- and energy-transfer reactions

Cadmium stress: an oxidative challenge

At the cellular level, cadmium (Cd) induces both damaging and repair processes in which the cellular redox status plays a crucial role. Being not redox-active, Cd is unable to generate reactive oxygen species (ROS) directly, but Cd-induced oxidative stress is a common phenomenon observed in multiple studies. The current review gives an overview on Cd-induced ROS production and anti-oxidative defense in organisms under different Cd regimes. Moreover, the Cd-induced oxidative challenge is discussed with a focus on damage and signaling as downstream responses. Gathering these data, it was clear that oxidative stress related responses are affected during Cd stress, but the apparent discrepancies observed in between the different studies points towards the necessity to increase our knowledge on the spatial and temporal ROS signature under Cd stress. This information is essential in order to reveal the exact role of Cd-induced oxidative stress in the modulation of downstream responses under a diverse array of conditions.

Mitochondria as a target for decavanadate toxicity in Sparus aurata heart

In a previous in vivo study we have reported that vanadium distribution, antioxidant enzymes activity and lipid peroxidation in Sparus aurata heart are strongly dependent on the oligomeric vanadate species being administered. Moreover, it was suggested that vanadium is accumulated in mitochondria, in particular when V10 was intravenously injected. In this work we have done a comparative study of the effects of V10 and monomeric vanadate (V1) on cardiac mitochondria from S. aurata. V10 inhibits mitochondrial oxygen consumption with an IC(50) of 400 nM, while the IC(50) for V1 is 23 microM. V10 also induced mitochondrial depolarization at very low concentrations, with an IC(50) of 196 nM, and 55 microM of V1 was required to induce the same effect. Additionally, up to 5 microM V10 did inhibit neither F(0)F(1)-ATPase activity nor NADH levels and it did not affect respiratory complexes I and II, but it induced changes in the redox steady-state of complex III. It is concluded that V10 inhibits mitochondrial oxygen consumption and induces membrane depolarization more strongly than V1, pointing out that mitochondria is a toxicological target for V10 and the importance to take into account the contribution of V10 to the vanadate toxic effects.

Bivalent metal ions modulate Cd2+ effects on isolated rat liver mitochondria

We have studied Cd2+-induced effects on mitochondrial respiration and swelling in various media as a function of the [Cd2+] in the presence or absence of different bivalent metal ions or ruthenium red (RR). It was confirmed by monitoring oxygen consumption by isolated rat liver mitochondria that, beginning from 5 microM, Cd2+ decreased both ADP and uncoupler-stimulated respiration and increased their basal respiration when succinate was used as respiratory substrate. At concentrations higher than 5 microM, Cd2+ stimulated ion permeability of the inner mitochondrial membrane, which was monitored in this study by swelling of both nonenergized mitochondria in 125 mM KNO3 or NH4NO3 medium and succinate-energized mitochondria incubated in a medium containing 25 mM K-acetate and 100 mM sucrose. We have found substantial changes in the above-mentioned Cd2+ effects on mitochondria treated in sequence with 100 microM of Ca2+, Sr2+, Mn2+ or Ba2+(Me2+) and 7.5 microM RR, as well as the alterations in Cd2+ action on the uptake of 137Cs+ by succinate-energized mitochondria in the presence or absence of valinomycin in acetate medium (50 mM Tris-acetate and 140 mM sucrose) with or without Ca2+ or RR. The evidence obtained indicate that Ca2+ exhibits a synergestic action on all Cd2+ effects examined, whereas Sr2+ and Mn2+, conversely, are antagonistic. In the presence of RR, the Cd2+ effects on respiration [stimulation of State 4 respiration and inhibition of 2,4-dinitrophenol (DNP)-uncoupled respiration] still exist, but are observed at concentrations of cadmium more than one order higher; the inhibition of State 3 respiration by Cd2+ conversely, takes place under even lower cadmium concentrations than those determined without RR in the medium. In addition, RR added simultaneously with cadmium in the incubation medium prevents any swelling in the nitrate media, but induces an increment both in Cd2+-stimulated swelling and 137Cs+ (analog of K+) uptake in the acetate media. For the first time, we have shown that Cd2+-induced swelling in all media under study is susceptible to cyclosporin A (CSA), a high-potency inhibitor of the mitochondrial permeability transition (PT) pore. The observations are interpreted in terms of a dual effect of cadmium on respiratory chain activity and permeability transition.

Effects of cadmium cell viability, trophoblastic development, and expression of low density lipoprotein receptor transcripts in cultured human placental cells

Previously, we have demonstrated that cadmium inhibits progesterone release in cultured human trophoblast cells. In the present study, we investigated potential mechanism(s) by which cadmium may elicit this effect. Cytotrophoblasts were obtained via enzymatic dispersion, purified by density gradient centrifugation, and cultured with increasing concentrations of cadmium. Cadmium-induced suppression of progesterone release seemed to be independent of cell death, as no significant decline in viability was observed with cadmium treatment. Further, immunocytochemical localization of cellular boundaries and nuclei indicated approximately 94% syncytial maturity was attained by both untreated and cadmium-treated cells, demonstrating that cadmium did not inhibit syncytial development. However, the abundance of LDL receptor (LDL-R) mRNA transcripts, as determined by competitive RT-PCR, was reduced (P < 0.05) by cadmium exposure in an apparent dose-dependent manner. Thus, the LDL-R, by which cholesterol substrate is supplied to the syncytiotrophoblast, is one site at which cadmium may interfere with placental progesterone production.

Immunotoxicity of low level cadmium exposure in fish: an alternative animal model for immunotoxicological studies

Cadmium represents a major aquatic pollutant in many parts of the world. Yet, despite the fact that cadmium accumulates in high concentrations in fish tissues, is found in polluted aquatic environments, and is carcinogenic and immunotoxic in a variety of mammalian species, the effects of cadmium on the immune responses of directly exposed aquatic species have not been clearly defined. This study was designed to assess the effects of in vivo cadmium exposure, at a concentration found in contaminated aquatic environments, on the immune defense mechanisms of fish. In this study, no effects were observed upon body weight, lysozyme activity, of cell viability, despite the high concentration of accumulated cadmium in the gills and liver. Furthermore, in the absence of any clinical manifestations or overt toxicity, exposure of rainbow trout to waterborne cadmium at 2 ppb altered macrophage-mediated immune functions, including phagocytosis and free radical production, in a time-dependent manner. Similar immunotoxic effects of cadmium have also been observed in mammals. Although interspecies comparisons between mammalian and fish immune responses are extremely complicated and need to be approached with caution, results from this study suggest the applicability of fish as an additional/alternative animal model for immunotoxicological studies.

Sudden infant death syndrome (SIDS): immunoglobulins and hypoxia

A body of opinion suggests that immunological overstimulation of the gastrointestinal and respiratory mucosa is involved in SIDS. The local stimulation of immunoglobulin concentration in the respiratory mucosa is said to be the consequence of an accentuated reaction to a trivial infection (1-4). One hypothesis is that an accentuated airways reactivity plays a key role in the events leading to SIDS and cites the final insult as oxygen lack, low oxygen stores, high oxygen usage and cardiorespiratory failure (5). We hypothesize that hypoxia and antioxidants exacerbate disorders of the paracrine interaction in the airways mucosa leading to overproduction of immunoglobulins. Administration of vitamin E above dietary needs to hypoxic chicks increased the immune response. The effects were considered synergistic in elevated production of immunoglobulins, and in their function as antioxidants (6). The oxygen lack, low oxygen stores, high oxygen usage and cardiorespiratory failure (5) are factors capable of provoking an overstimulated immune response in the respiratory mucosa. When levels of T-helper/inducer cells are maintained in AIDS patients' blood plasma, survival time is extended (7). This paper investigates the role of 1,25 (OH) 2D3 in suppression of T-helper/inducer lymphocyte activity in vitro (8,9,34,36), and the failure of activated pulmonary alveolar macrophages (PAM) to produce sufficient 1,25(OH)2D3 to inhibit beta-cell proliferation before differentiation to immunoglobulin secreting cells (4,36).

Cadmium ion-induced alterations of phospholipid metabolism in endothelial cells

Cadmium exposure is capable of causing acute and chronic lung injuries, but the specific pathogenetic mechanisms are uncertain. The effects of cadmium ion (Cd2+) on phospholipid metabolism were examined in cultured bovine pulmonary artery endothelial cells (BPAEC), as endothelial cells appear to be particularly vulnerable to the toxic effects of this metallic ion. Exposure of radiolabeled BPAEC to millimolar concentrations of Cd2+ causes liberation of substantial amounts of [3H]arachidonic acid ([3H]AA), but only small amounts of [14C]stearic acid, from each of the major phospholipid subclasses. Analyses of hydrolytic products in BPAEC radiolabeled with [3H]myo-inositol and exposed to Cd2+ indicate that degradation of complex phospholipids is mediated by phospholipase A2. The ability of BPAEC to incorporate fatty acids or lysophosphatides into complex phospholipids is similarly impaired after exposure to Cd2+, suggesting that the liberation of [3H]AA might be due to impairment of reacylation mechanisms and not to increased hydrolytic activity of phospholipase A2. Of the two enzymes involved in reacylation reactions, Cd2+ is found to inhibit the activity of arachidonyl-specific acyl coenzyme A synthetase but not the activity of acyltransferase. Cd2+ also causes a profound time- and dose-dependent depletion of adenosine triphosphate levels in BPAEC, and these changes closely correlate with the liberation of [3H]AA. We suggest that impairment of reacylation mechanisms, and the consequent accumulation of arachidonic acid, may be important in the development of the acute inflammatory reaction that is characteristic of Cd(2+)-induced lung injury.

Effects of cadmium in freshwater clams. III. Interaction with energy metabolism inAnodonta cygnea

Freshwater clams,Anodonta cygnea, were exposed to cadmium, at 50 ppb (μg/L), to investigate the effects of semi-chronic exposure on energy metabolism. Parameters examined included: adenylate energy charge (AEC), glycogen content, blood glucose and protein concentration, the accumulation of anaerobic metabolic end products,viz. lactate and succinate, and mitochondrial NADH-oxidase activity. In all tissues, AEC was significantly lowered after 12 weeks. Glycogen contents of the separate organs, except for the gills, were diminished to one half those of control animals. Hemolymph glucose increased between 4 and 8 weeks, whereas protein in hemolymph steadily decreased, to about one half the concentration of controls at 12 weeks. Lactate increased in mantle and midgut gland, whereas in gill only an initial accumulation was found after 2 weeks of exposure. Succinate concentrations increased in all organs between 4 and 8 weeks of Cd exposure. Thereafter, no further accumulation occurred. From the onset of exposure to cadmium there was a gradual reduction of NADH-oxidase activity of gill mitochondria, down to 60% of the control value after 12 weeks. The data indicate an impairment of oxidative carbohydrate metabolism that is brought about by a metabolic blockade, rather than by (partial) anaerobiosis as a consequence of shell closure.

Inhibition of rat heart mitochondrial respiration by cadmium chloride

Mitochondria were isolated from hearts obtained from adult male Sprague-Dawley rats by two-part differential centrifugation of heart homogenates. Time-dependent (0-120 sec) and concentration-dependent (0-10 microM CdCl2) effects of cadmium on pyruvate-malate-supported state 3 and state 4 respiration were measured in a constant temperature reaction chamber at 37 degrees C, according to established procedures. The ID50 for cadmium chloride on state 3 respiration was determined to be 4.2 microM. The inhibition produced by cadmium chloride in heart mitochondria was compared, using identical procedures, to the effects induced by two compounds, sodium atractyloside and potassium cyanide, which are known to alter mitochondrial respiration at specific sites. The calculated ID50 values for these agents in heart mitochondria were 1.8 and 16 microM, respectively. The concentration-dependent inhibition of mitochondrial respiration induced by either cadmium chloride or potassium cyanide was maintained in the presence of 50 microM carbonyl cyanide m-chlorophenylhydrazone (CCCP), a known uncoupling agent. In contrast, sodium atractyloside did not block the uncoupling effect of 50 microM CCCP. In addition cadmium chloride was also shown to inhibit CCCP-uncoupled mitochondrial respiration. The cadmium-induced inhibition of mitochondrial respiration was reversed partially by cysteine and completely by 2,3-dimercaptopropanol. The results of the present study indicate that, at all concentrations, cadmium chloride acted solely as an inhibitor of rat heart pyruvate-malate-supported mitochondrial respiration. These findings suggest a possible mechanism for the reported disturbances in myocardial metabolism and function that occur in conjunction with acute and chronic cadmium exposure in humans and experimental animals.

Pulmonary cadmium oxide toxicity in the rat

Although occupational exposures to cadmium have usually involved inhalation of insoluble cadmium oxide (CdO) particles, experimental studies of pulmonary cadmium toxicity have relied on aerosol exposures to soluble cadmium chloride particles. The present study describes a model of acute lung injury based on single 3-h exposures of rats to 0.5 and 5.3 mg/m3 CdO. Biochemical changes were correlated with pathological observations for 15 d postexposure to CdO. Four days following CdO exposure, histopathological observations included focal areas of epithelial hyperplasia, a mononuclear interstitial infiltrate, and increased numbers of alveolar macrophages. In the high-dose group, these changes were correlated with increases in tissue protein and DNA contents of 217% and 195% of controls, respectively. While lungs from the low-dose exposures had returned to a normal appearance by 15 d postexposure, high-dose-exposed lungs exhibited an increase in noncellular thickening of the interstitium and a continued general hypercellularity at this time. In the high-dose exposure group, activities of the enzymes glutathione peroxidase, glutathione reductase, and the dehydrogenase of glucose 6-phosphate and 6-phosphogluconate were significantly elevated two- to fivefold at 2-4 d postexposure. When a correction was made for changes in lung cell number, significant increases were observed only in activities of the pentose-cycle dehydrogenases at 180-238% of controls. These increases suggested an enhanced ability of CdO-exposed lungs to generate the pentose-cycle products NADPH and ribose 5-phosphate, which would be needed for lipid and nucleic acid biosynthesis expected during the proliferative stages of epithelial repair. This study has demonstrated that the response to CdO exposure includes the induction of enzymatic activities that are related to antioxidant defense and lung repair.

The effects of cadmium on succinate and NADH-linked substrate oxidations in rat hepatic mitochondria

Low concentrations of cadmium (3.3-40 microM) inhibited State 3 NADH-linked respiration in rat hepatic mitochondria, but failed to release oligomycin (1 microgram) inhibited State 3 respiration, or to significantly change the State 4 rate. In the presence of succinate, 40 microM cadmium inhibited State 3 respiration by 89%, while concentrations between 3.3 and 13.3 microM stimulated State 4 respiration. Higher concentrations caused marked inhibition. In the presence of succinate, cadmium released oligomycin inhibited State 3 respiration. Cadmium (0.001-1.0 mM) did not stimulate mitochondrial ATPase activity or inhibit ferricyanide reduction, but stimulated NAD+ linked mitochondrial dehydrogenase activities and NADH oxidation. These results indicate that cadmium interacts with either the NADH dehydrogenase complex or other NADH-dependent enzymes and not solely by an uncoupling action.

Effects of cadmium inhalation on mitochondrial enzymes in rat tissues

Pulmonary and extrapulmonary effects from a 2-h inhalation exposure to cadmium (850 micrograms Cd/m3) were studied in male rats. The effect of this chemical on mitochondrial enzyme activity in the lung, liver, kidney, and testis were investigated immediately after exposure and at 48, 144, and 336 h postexposure. In all tissues studied, mitochondrial citrate synthase activity was significantly increased immediately after the cessation of the exposure. This activity level began to decrease at 48 h postexposure. Succinic dehydrogenase activity was significantly decreased in the lungs and kidney at all periods tested, but increased activity was seen in the liver and testis. Cytochrome c oxidase activity in lungs and testis mitochondria was inhibited at all time periods studied. In the liver and kidney this activity was significantly increased immediately after the exposure ceased, and then a significant reduction began to appear at 48 h postexposure. This study demonstrates that inhaled cadmium, after deposition in the lungs, may alter various enzyme activities in other organs.

Cadmium accumulation in organs of the scallop Mizuhopecten yessoensis--I. Activities of phosphatases and composition and amount of lipids

Maintenance of Mizuhopecten yessoensis in water with 0.5 mg Cd/l for 60 days increased Cd concentration in the mantle and ovaries about 200 times, in gills 70 times and hepatopancreas 20 times. Alkaline phosphatase activity was inhibited in all organs except the hepatopancreas after a 1-month exposure to Cd and became equal to the control in all the organs after 2 months exposure. Molluscs transferred to flowing water showed a considerable decrease in the activity of alkaline and acid phosphatases. The activity of both acid phosphatase and Mg2+-ATPase decreased in all the organs of experimental molluscs after exposure to Cd. The amount of phospholipids and cholesterol in the organs of control and experimental molluscs did not essentially differ.

A comparison of the cellular toxicity of exhausts from cars driven on present and future fuels

A cellular test system (brown-fat-cell-test) (BFC-test) has been used to evaluate the toxicity of the particulate phase of exhaust emission from vehicles fuelled with gasoline and alcohol-mixed fuels. The results were evaluated by an analysis of variance with multiple contrasts. The exhaust extracts from cars driven on commercially available gasoline were found to be significantly more toxic to the cellular oxygen consumption than a similar extract of exhausts from cars driven on alcohol-mixed fuels. The lowest toxicity was found with extracts from catalyst processed exhausts.

Effects of air pollutants on the oxidative metabolism and phagocytic capacity of pulmonary alveolar macrophages

Isolated rabbit pulmonary alveolar macrophages were found to be a convenient biological model system, relevant for studies of the toxicity of air pollutants. The phagocytic capacity and the oxygen consumption were used as test parameters and studied simultaneously on the same cells. The toxicity of extracts of airborne particles (phi less than 15 microns) collected in urban and rural areas was investigated and compared to a cigarette-smoke condensate. An extract of particles from a car tunnel was found to be the most toxic air sample, inhibiting phagocytosis as well as respiration of the macrophages at a concentration representing 5 m3 air/ml cell suspension. A corresponding sample collected on a roof of a five-storied building in the central area of a city (population 600,000) was found to inhibit phagocytosis but did not affect respiration. Further investigations revealed that one effect of the "tunnel" extract could be explained as an uncoupling of the mitochondrial respiratory control. Compared to the cigarette-smoke condensate, the toxicity of the air samples was infinitesimal.

Effects of intraperitoneal cadmium administration on mitochondrial enzymes in rat tissues

The effects of cadmium on some mitochondrial enzymes of kidney, testis and lung were investigated in male rats. Rats were injected intraperitoneally with 3 mg Cd/kg body weight and its effects were studied 24, 72 and 144 h later. Succinic dehydrogenase and cytochrome c oxidase activities were significantly inhibited in kidney, testis and lung mitochondria. Citrate synthase activity was inhibited in testis mitochondria at all time periods studied, whereas in kidney and lung an initial increase in activity was followed by inhibition at later time periods.

Drug-induced lipidosis and the alveolar macrophage

The alveolar macrophage is the principal component of the defense mechanisms of the lung. As a result, alterations in its function can predispose the host organism to pulmonary disease or damage. This cell shows toxic responses to a wide variety of chemicals which are delivered to the lungs by either inhalation or via the systemic circulation. In this regard, this review will focus on the effects of a group of cationic amphiphilic drugs which when administered to humans and animals causes a lysosomal storage disorder of lipids, principally phospholipids, in alveolar macrophages. The susceptibility to the disorder is species-dependent and can be induced in fetal, neonatal and adult animals. Evidence exists that the accumulation of lipids within the cells occurs as a result of an impairment in lipid catabolism, however, not all of the available data are consistent with this theory. In light of this, other mechanisms to explain the etiology of this lipidosis are discussed. Associated with the increase in lipid content within the cell, striking morphological, biochemical and functional changes occur to the alveolar macrophage. Available data indicate that afflicted cells have an increased phagocytic activity and exhibit enhanced killing of one strain of bacteria. While these data suggest an enhancement in certain cellular functions, inadequate information presently exists to allow conclusions to be drawn concerning the consequences of this disorder.

Stimulation of dehydrogenase synthesis by cadmium in a cadmium-resistant strain of Saccharomyces cerevisiae

The activity of dehydrogenase in Saccharomyces cerevisiae was estimated by reduction of 2,3,5-triphenyltetrazolium chloride. By the adaptation of yeast to cadmium, the high activity of dehydrogenase was observed. Furthermore, the activity of dehydrogenase in Cd-resistant cells was increased by growing in medium containing CdSO4. However, the activity of dehydrogenase was inhibited by the addition of CdSO4 to the reaction mixture. The activity of dehydrogenase in Cd-sensitive cells was increased slightly by incubation with low concentrations of CdSO4. High activity of dehydrogenase in Cd-resistant cells was completely negated by the addition of cycloheximide to the incubation medium. The increase of dehydrogenase activity is due partly to de novo synthesis of protein.

Influence of cadmium on the phagocytic and microbicidal activity of murine peritoneal macrophages, pulmonary alveolar macrophages, and polymorphonuclear neutrophils

A significant depression in the phagocytic capacity of elicited peritoneal macrophages, pulmonary alveolar macrophages, and elicited peritoneal polymorphonucleated neutrophils was manifested when the cells were incubated in medium containing cadmium chloride. With the exception of the neutrophils, a similar influence was observed when the cells were exposed to cadmium acetate. The impaired phagocytic capacity was related to the concentration of the cadmium in the medium. Peritoneal macrophages and neutrophils did not demonstrate any alteration in their microbicidal activity (percentage of ingested yeast which were killed) in the presence of the cadmium salts. However, a significant suppression in the intracellular microbicidal activity of alveolar macrophages was observed when the cells were incubated in medium containing either cadmium chloride or cadmium acetate. This unique response to Cd2+ may be related to general metabolic characteristics of these cells living at an elevated O2 tension.

Distribution of cadmium in developing teeth and bone of young rats

109-Cadmium was injected intraperitoneally into 10-d-old rats. The rats were terminated at 1, 4, 24 and 96 h postinjection. Distribution of the tracer was studied by autoradiographic techniques, with particular attention directed to the dental tissues. Considerable accumulation of 109-cadmium occurred in the cells of the enamel and dentin was observed. The injected cadmium was also accumulated in the growing bone. Microautoradiography seemed to indicate that the isotope was preferentially localized in the osteoblasts.