Effect of acute oral cadmium on mitochondrial enzymes in rat tissues

Cadmium and mitochondria

The heavy metal cadmium (Cd) a pollutant associated with several modern industrial processes, is absorbed in significant quantities from cigarette smoke, water, food and air contaminations. It is known to have numerous undesirable effects on health in both experimental animals and humans, targeting kidney, liver and vascular system. The molecular mechanism accounting for most of the biological effects of Cd are not well-understood and the toxicity targets are largely unidentified. The present review focuses on important recent advances about the effects of cadmium on mitochondria of mammalian cells. Mitochondria are the proverbial powerhouses of the cell, running the fundamental biochemical processes that produce energy from nutrients using oxygen. They are among the key intracellular targets for different stressors including Cd. This review provides new additional informations on the cellular and molecular aspects of the interaction between Cd and cells, emphasizing alterations of mitochondria as important events in Cd cytotoxicity, thus representing an important basis for understanding the mechanisms of cadmium effect on the cells.

Sudden infant death syndrome: hypothalamic failure to sense elevated blood pyrogens

Sudden infant death syndrome (SIDS) is frequently associated with a mild infection, the incidence peaking during the third month of life. We hypothesize that the neonatal immaturity of both the acute febrile response and hypothalamus promote neonatal protection from SIDS. Vagal afferents modify the febrile response. Vagotomized rodents displayed a loss of febrile responsiveness in a 'non-sensing' brain. The failure of a 'non- sensing' brain to react to elevated blood pyrogens leads to failure of the febrile response and to a shock-like state. SIDS infants may appear well yet, within hours of this observation, may be found dead. There is a mismatch between the acute febrile response and hypothalamic hypoactivation. The discrepancy increase wtih development. There is an elevated cytokine response in endothelial cells which induces nitric oxide (NO) production and retarded development of the hypothalamus. Cigarette smoke also induces NO production and retards hypothalamic development by augmented apoptosis. Zinc inhibits this effect in mouse thymocytes. Fetal haemoglobin (HbF) induces hypoxia which is a stimulator of the immune response, while vasodilator gases (carbon monoxide (CO), NO) reduce hypothalamic function. The hypothalamic failure to sense elevated blood pyrogens induces toxic shock--a feature of SIDS.

Sudden infant death syndrome: hypothalamic failure to sense elevated blood pyrogens

Sudden infant death syndrome (SIDS) is frequently associated with a mild infection, the incidence peaking during the third month of life. We hypothesize that the neonatal immaturity of both the acute febrile response and hypothalamus promote neonatal protection from SIDS. Vagal afferents modify the febrile response. Vagotomized rodents displayed a loss of febrile responsiveness in a 'non-sensing' brain. The failure of a 'non-sensing' brain to react to elevated blood pyrogens leads to failure of the febrile response and to a shock-like state. SIDS infants may appear well yet, within hours of this observation, may be found dead. There is a mismatch between the acute febrile response and hypothalamic hypoactivation. The discrepancy increases with development. There is an elevated cytokine response in endothelial cells which induces nitric oxide (NO) production and retarded development of the hypothalamus. Cigarette smoke also induces NO production and retards hypothalamic development by augmented apoptosis. Zinc inhibits this effect in mouse thymocytes. Fetal haemoglobin (HbF) induces hypoxia, which is a stimulator of the immune response while vasodilator gases (carbon monoxide (CO), NO) reduce hypothalamic function. The hypothalamic failure to sense elevated blood pyrogens induces toxic shock - a feature of SIDS.

Effect of cadmium on membrane potential in isolated rat hepatocytes

The effect of cadmium (Cd) on rat hepatocytes upon short term exposure was studied by focusing on the integrity of mitochondria and on the possible consequences of its disturbance, such as alterations in plasma membrane potential and loss of cell viability. Changes in the potential of mitochondrion and plasma membranes were monitored using [3H]triphenylmethylphosphonium (TPMP+) and [14C]SCN- probes, respectively. Isolated rat hepatocytes were exposed to increasing CdCl2 concentrations for short time periods (30-120 min). Cd measurement by atomic absorption showed that the cells efficiently accumulated Cd, as did mitochondria in situ. In CdCl2-treated cultures, it was observed that the release of TPMP+, which revealed a drop in the mitochondrial membrane potential, was time- and concentration-dependent, and that the first significant efflux was caused by a 30-min exposure to 89 microM CdCl2. No significant change in plasma membrane potential, as judged from the increase in the uptake of SCN-, was detected after 30 min, suggesting the greater precocity of the mitochondrial attack. Finally, the release of lactate dehydrogenase (LDH) occurred only after 2 h of exposure, reflecting ultimate stages of cell injury induced by Cd. These results suggest that Cd induces an alteration in mitochondrial function in hepatocytes which may lead to the loss of plasma membrane potential and cell viability. The study therefore adds further evidence of the role of mitochondria as primary targets in Cd-induced cytotoxicity.

Subclinical response to cadmium in liver cells

Effects of cadmium (Cd) in vivo and in vitro were studied in the absence of enhanced metallothionein (MT) production and overt Cd toxicity. Such a condition was established by extended oral exposure of male rats to 0.2 mumols Cd/kg and by incubation of isolated hepatocytes with up to 25 microM for 30 min. Subsequently, mitochondrial and extramitochondrial responses to Cd were recorded. Cadmium diminished the activity of cytochrome c oxidase (CYT C OX) by 50% in vivo and by 35% in vitro. In hepatocytes, this was accompanied by increased Cd and decreased protoheme (PrH) in mitochondria. Extramitochondrial PrH and cytochrome P 450 were not significantly altered. In hepatocytes from phenobarbitone pretreated rats, 25 microM Cd decreased CYT C OX but not mitochondrial PrH. Moreover, stimultaneous incubation of hepatocytes with 25 microM Cd and either 2.5 mM dithiothreitol or 5 mM reduced glutathione diminished cellular and mitochondrial Cd and prevented the decrease in CYT C OX but not that in PrH. In contrast, coincubation with either 250 microM L-buthionine-sulfoximine or diethylmaleate, which did not alter Cd uptake, prevented the decrease in PrH but not that in CYT C OX owing to Cd. These results show that Cd exerts mitochondrial alterations in vivo and in vitro in the absence of enhanced MT production. Moreover, Cd effects on CYT C OX and PrH do not seem to be firmly linked.

Response of rat hepatocyte cultures to cadmium chloride and cadmium-diethyldithiocarbamate

Cellular effects of cadmium (Cd) were studied in primary cultures of rat hepatocytes incubated with cadmium chloride (CdCl2) or cadmium-diethyldithiocarbamate (Cd(DTC)2), labelled with 109Cd. The lipid-soluble complex Cd(DTC)2 was rapidly taken up into the cells and a maximal concentration was reached after 4 h incubation. On the other hand, incubation with CdCl2 resulted in a slow, continuous accumulation of Cd for up to 20 h. Cd was found to be associated with proteins to a higher extent when added to the incubation medium as CdCl2 than when added as Cd(DTC)2, which in addition to differences in lipophilicity of the Cd compounds partly explains the differences in Cd uptake. Subcellular distribution studies showed that a significantly higher proportion of Cd was associated with the total particulates fraction in cells after incubation with Cd(DTC)2 compared to CdCl2 (32 and 19%, respectively). The activities of glutathione reductase and succinic dehydrogenase were inhibited to a similar extent by the 2 Cd compounds. Alcohol dehydrogenase was more strongly affected by CdCl2 than by Cd(DTC)2, although the uptake of Cd was 3-4 times higher in cells incubated with Cd(DTC)2 than in those incubated with CdCl2. The results from the present study show that DTC can increase the transport of Cd into the cell by complex formation with Cd. Compared to CdCl2 the Cd(DTC)2 complex was less toxic as indicated by the biochemical parameters used.

Subcellular toxicity of low level cadmium in rats: effect on cytochrome c oxidase

The in vivo effect of cadmium (Cd) with or without prior administration of L-cysteine (Cys) or diethylmaleate (DEM) on hepatic and renal cytochrome c oxidase (Cyt-c-Ox), essential metals and mitochondrial thiols was investigated. Male Sprague-Dawley rats were given 25 micrograms Cd/kg (as Cd acetate) orally 5 times a week for 6 weeks. Different groups of animals additionally received either Cys (500 mg/kg per day, p.o.) or DEM (0.85 mg/kg, i.p.) by multiple administration. Parameters were determined 1 day after the last gavage. Cadmium decreased the activity of Cyt-c-Ox in mitochondria of livers but not in those of kidneys. Copper in both tissue and mitochondria were unaffected whereas hepatic tissue iron decreased by 50% upon Cd gavage. Cysteine pretreatment increased hepatic and especially renal mitochondrial Cd, but diminished the Cd effect on Cyt-c-Ox and increased hepatic tissue iron. Both DEM and DEM/Cd treatment decreased Cyt-c-Ox by 50% in liver but not in kidneys. Metallothionein was not significantly altered by either treatment. Considering data from all the experimental groups Cyt-c-Ox activity seems to be related rather to the amount of protein thiols than to either copper or iron in hepatic mitochondria. The data demonstrate the high susceptibility of hepatic vs. renal mitochondria and suggest the involvement of thiols in Cyt-c-Ox activity.

A cadmium-binding protein in rat liver identified as ornithine carbamoyltransferase

A cadmium-binding protein of Mr about 40,000 (40K Cd-BPa) was detected in rat liver by Western blotting [Aoki, Kunimoto, Shibata & Suzuki (1986) Anal. Biochem. 157, 117-122]. It was characterized and identified as ornithine carbamoyltransferase (OCTase, EC 2.1.3.3) on the basis of coincidence of their physicochemical and enzymological features. The amino acid sequence of the N-terminal and those of three tryptic digests in 40K Cd-BPa were identical with those of OCTase. The Mr values of the denatured and native forms of 40K Cd-BPa (39,000 and 110,000 respectively) were the same as those of OCTase. 40K Cd-BPa showed, as OCTase activity, a specific activity of 230 mumol/min per mg of protein and Km of 0.6 mM for ornithine, this value also being essentially the same as that for OCTase. A rabbit antibody against OCTase reacted with 40K Cd-BPa. The native form of 40K Cd-BPa bound to 0.8 molar equiv, of cadmium, with a dissociation constant of 7.6 x 10(-6) M.

Sudden infant death syndrome: congenital copper deficiency

A previous paper describes specific respiratory toxins likely to be associated with Sudden Infant Death Syndrome (SIDS). This paper describes ultrastructural abnormalities in the lung and other tissues in congenital copper deficiency. Congenital copper deficiency is associated with tissue anoxia defects in the development of myelin through a failure of phospholipid synthesis. Phospholipid is part of the membrane structure of cells. The paucity of elastin is attributed to a loss of lysyl oxidase activity. Hypoventilation is considered a feature of SIDS.

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.

Calcium-dependent effects of cadmium on energy metabolism and function of perfused rat heart

Postequilibrated isolated rat hearts were perfused for 60 min with a standard supporting electrolyte buffer containing one of the following calcium concentrations: 0.9, 1.8, 3.5, or 5.0 mM, either with or without added cadmium. Doses of cadmium which proved to be minimally (0.03 microM Cd)--and maximally (3.0 microM Cd)--effective at 0.9 mM Ca were studied at all other calcium concentrations. A dose-dependent positive inotropy that persisted throughout the 60-min perfusion period was induced by the graded increases in the perfusate calcium concentration throughout the range from 0.9 to 5.0 mM. Atrioventricular node conductivity was prolonged significantly in hearts perfused with 0.9 mM Ca as compared to hearts perfused with higher calcium concentrations. Increasing the perfusate calcium concentration caused a dose-dependent increase in heart glycerol 3-phosphorylcholine (GPC) content. The other measured phosphatic metabolites of the heart were not altered significantly by varying the perfusate calcium level. In contrast, cadmium (3.0 microM Cd) induced extensive functional and metabolic aberrations which varied in magnitude as an inverse function of the perfusate calcium concentration. Contractile tension, rate of tension development (dT/dt), heart rate, coronary flow rate, and atrioventricular node conductivity were decreased significantly in response to cadmium perfusion. Moreover, these hearts characteristically had significantly elevated low energy phosphate (inosine monophosphate and inorganic phosphate) and decreased high energy phosphate (ATP, PCr) levels relative to their respective calcium controls. Furthermore, various phosphorylated intermediates of glycolysis (glucose 6-phosphate, fructose 6-phosphate, glucose 1-phosphate), as well as glycerol 3-phosphate, and uridine diphosphoglucose accumulated significantly in hearts perfused with cadmium at certain calcium concentrations below 5.0 mM. The calcium-activated increase in heart GPC was inhibited completely by 3 microM cadmium. At the minimally effective dose of cadmium (0.03 microM), demonstrable changes were apparent only at the lowest perfusate calcium concentration examined (0.9 mM). These findings are consistent with the hypothesis that cadmium interferes with calcium-activated and calcium-mediated physiologic and biochemical processes of the mammalian heart. The primary mechanistic basis for the action of cadmium appears to be linked to a competition with calcium for membrane and possibly intracellular binding and activation sites.