The dual effects of aluminum as activator and inhibitor of adenylate cyclase in the liver fluke Fasciola hepatica

Influence of aluminum on the regulation of PTH- and 1,25(OH)2D3-dependent pathways in the rat osteosarcoma cell line ROS 17/2.8

The role of hormonal status in the development of aluminum (Al)-dependent renal osteodystrophy, which is characterized by reduced bone matrix deposition, still remains largely unknown. To address this question, we used the osteoblast-like osteosarcoma cell line ROS 17/2.8 to evaluate the role of Al on parathyroid hormone (PTH)- and 1,25-dihydroxyvitamin D3 (1,25(OH)2D3)-dependent activities in these cells. Al (1 microM) caused an inhibition of basal and 1,25(OH)2D3-induced alkaline phosphatase, but only at low doses (< 1 nM) of the steroid. Al partly inhibited basal osteocalcin (OC) secretion in ROS cells (p < 0.001), and the dose-dependent increase in 1,25(OH)2D3-induced OC release by these cells was also reduced by 1 microM Al at low concentrations of the steroid (< or = 1 nM), whereas high doses of 1,25(OH)2D3 (> or = 5 nM) totally prevented the inhibiting effects of Al. Al also had strong inhibitory actions on PTH-dependent cAMP production by ROS cells over the concentration range tested (0.5-50 nM). This inhibitory action of Al was also observed for PTH-related peptide- (PTHrp, 50 nM) but not for Isoproterenol-dependent (100 nM) cAMP formation. To evaluate more fully the mechanism of this inhibition of cAMP formation, we investigated the effect of Al on toxin-modulated, G protein-dependent regulation of cAMP formation and on the activation of adenylate cyclase by Forskolin. Cholera toxin (CT, 10 micrograms/ml), applied to cells for 4 h prior to PTH challenge, enhanced cAMP production about 2-fold above PTH alone (p < 0.001), a process that was further stimulated by Al. Pertussis toxin (PT, 1 microgram/ml, 4 h) did not modify basal PTH-dependent cAMP formation by ROS cells. However, PT treatment prevented the inhibitory effect of Al on cAMP formation by these cells (p < 0.025). The stimulation of adenylate cyclase by Forskolin (0.1 and 1 microM), which bypasses G protein regulation, was not modified by Al, indicating that Al does not affect adenylate cyclase directly. Northern blot analysis of PTH receptor mRNA levels showed that Al did not modify PTH receptor message in ROS cells. Likewise, Western blot analyses of G protein subunits showed that Al did not significantly alter Gs alpha subunit levels, in accordance with the results obtained for cAMP-dependent formation in response to CT. In contrast, Gi alpha-1 and Gi alpha-2 subunits were decreased by Al treatment, consistent with PT-restricted increases in cAMP formation in Al-treated ROS cells. Taken together, these results suggest that Al has multiple actions in osteoblast-like ROS cells. The effects of Al are modulated by hormonal control of the pathways investigated. Al affects 1,25(OH)2D3-regulated functions only when this steroid is low. Al has large inhibitory effects on PTH- and PTHrp-dependent cAMP formation. This last feature is related to the ability of Al to alter the G protein transducing pathway for PTH/PTHrp-dependent formation of cAMP since it does not affect adenylate cyclase activity directly and does not affect the PTH receptor message level. Thus, Al has stronger deleterious effects in osteoblast-like cells with an already compromised 1,25(OH)2D3 status and can modulate specifically PTH/PTHrp-mediated cAMP formation at the postreceptor level.

Aluminium-induced bone disease in uremic rats: effect of deferoxamine

We have previously established a rat model of chronic uremia, which is suitable to investigate the effect of various treatment modalities on renal osteodystrophy [1]. After four months subsequent to 5/6 nephrectomy, some animals were treated by gavage for 9 weeks with tap water (controls), or with aluminium (Al-citrate) 3 x 25 mg/week/kg b.wt +/- subsequent deferoxamine (DFO) 3 x 50 mg/week/kg b.wt. for 4 weeks. At termination of the study, serum clinical chemistry, femoral chemical composition and mechanical properties, calvarial parathyroid hormone (PTH)-elicited adenylate cyclase (AC) and phospholipase C (PLC) activities, cross-sectional femoral area, as well as bone histomorphometry, were analyzed. Animals given Al displayed moderately enhanced serum Al and bone Al accumulation, however, DFO-treatment did not fully alleviate bone Al retainment. A small increase in serum PTH was seen in all animals rendered uremic. Furthermore, a marked fall in serum alkaline phosphatase (ALP) below normal controls was observed in Al +/- DFO-treated animals compared with uremic controls. The uremic condition led to reduced femoral ratios of hydroxyproline (HYP) over Ca(2+) and phosphate (P(i)), while Al-intoxication alone enhanced femoral Hyp contents above values seen for normal controls. The protracted ureamia caused a deterioration of long bone resilience and brittleness, however, Al +/- DFO-treatment seemed to normalize the latter. Contrastingly, Al +/- DFO-gavage enhanced time to fracture. Uremic rats intoxicated with Al showed a complete loss of calvarial PTH-sensitive AC and PLC activities. DFO-treatment normalized PTH-elicited PLC, while PTH-susceptible AC remained super-normal. Al apparently exerts a long term down-regulation of both PTH-sensitive signaling systems as evidenced by studies of rat UMR 106 osteosarcoma cells in culture. The uremic condition enhanced endosteal bone resorption as shown by femoral shaft dimension analysis, while Al +/- DFO-treatment insignificantly reversed the condition. Finally, histomorphometrical analyses showed that DFO-administration tended to normalize aberrant trabecular bone volume, while rectifying both bone resorption and degree of mineralization. In conclusion, we assert that Al-intoxication hampers both processes (i.e. formation and resorption) of bone turnover, and that DFO-treatment to a certain extent prevents the uremia- and Al-induced bone disease in rats.

Aluminum interaction with phosphoinositide-associated signal transduction

Concerning molecular and cellular mechanisms of aluminum toxicity, recent studies support the hypothesis that interactions of aluminum ions with elements of signal transduction pathways are apparently primary events in cells. In the case of the phosphoinositide-associated signalling pathway of neuroblastoma cells, guanine nucleotide-binding proteins (G proteins) and a phosphatidylinositol-4,5-diphosphate (PIP2)-specific phospholipase C are probable interaction sites for inhibitory actions of aluminum ions. Following interiorization of aluminum by the cell, metal interactions decrease the accumulation of inositol phosphates, especially that of inositol-1,4,5-triphosphate (IP3), concomitant with derangements of intracellular Ca2+ homeostasis. In the presence of high concentrations of Ca2+, formation of IP3 is also diminished in aluminum-pretreated cells, presumably involving a process not requiring Mg(2+)-dependent G proteins. At higher aluminum doses, metal-induced changes in the lipid milieu of the membrane-bound phospholipase may play a role. These types of primary interactions of aluminum ions with elements of cellular communication channels are probably crucial in the manifestation of the multifacetted aluminum toxicity syndrome. If present as a phosphate-like fluoro-aluminate, a stimulatory role of aluminum ions is displayed in G protein-coupled transmembrane signalling.

Concerning stimulation by injected fluoroaluminate of the sodium efflux in barnacle muscle fibers

Single barnacle muscle fibers from Balanus nubilus were used primarily to examine the validity of two ideas: first, that the injection of KF stimulates the ouabain-insensitive Na+ efflux, and that this action is potentiated by adding AlCl3 (Al) in a low concentration to the solution of KF prior to injection. And second, that the injection of a KF-AlCl3 solution into ouabain-poisoned, K(+/-)-depolarized fibers elicits a stimulatory response resembling that obtained by injecting GTP. The results of this study are as follows: injection of 0.5 M KF into unpoisoned fibers causes a sustained rise in the resting Na+ efflux. However, injection of a 0.5 M KF, 10(-3) M AlCl3 solution leads to a reduced rather than an augmented response. Whereas injection of 0.5 M KF into ouabain-poisoned fibers elicits a marked stimulatory response, the injection of 0.5 M KF, 10(-3) M AlCl3 reduces the remaining Na+ efflux. Injection of KF-AlCl3 in equimolar concentrations, e.g., 0.25 M, elicits a response that is significantly larger than that obtained by injecting 0.25 M KF. A dose-response curve indicates that a 0.2 M solution of fluoroaluminate probably represents an optimal concentration. Injection of 0.3 M KF following peak stimulation by injecting 0.3 M AlCl3 completely reverses this response to Al. In sharp contrast, injection of a 0.3 M KF, 0.3 M AlCl3 mixture following peak stimulation by injecting 0.3 M AlCl3 is ineffective. Injection of KF into ouabain-poisoned, K+ depolarized fibers does not always cause sustained stimulation of the remaining Na+ efflux.(ABSTRACT TRUNCATED AT 250 WORDS)

Hematological effects of aluminum on living organisms

1. Aluminum has been of great interest for many researchers over a number of years; its biochemical and physiological role is not yet fully clear. There are few papers describing the hematological consequences of its excess in living organisms and most of their data are cited in this paper. 2. Aluminum reduced the deformability of erythrocytes, and such cells are rather frequently retained in the reticuloendothelial system of the spleen and eliminated faster from the blood stream. 3. Aluminum produces peroxidative changes in the erythrocytes membrane, leading to hemolysis. Therefore, the depressed erythrocyte count in animals intoxicated with aluminum may be the consequence of both the hemolytic action of aluminum and the shortened time of survival of erythrocytes. 4. It was demonstrated that aluminum inhibits heme biosynthesis in vitro. This problem requires, however, further studies and observation. 5. Changes occurring under the influence of Al3+ on the leukocyte system of animals suggest the influence of this element on the resistance of the organism, but the mechanism of the action of Al3+ still requires elucidation. 6. Cell metabolism including blood cells may be affected by aluminum in many ways, the more so as the element may combine in vitro with amino acids, peptides, proteins, enzymes, substrates, cofactors, nucleotides and carbohydrates. Aluminum stimulates NADPH oxidation and takes part in the process of free radical formation.

Is there any relationship between aluminum and Alzheimer's disease?

The controversial role of aluminum in Alzheimer's disease (AD) is reviewed. While current data would suggest the lack of a causative role, alterations in the brain and other organ systems caused by AD might increase the penetration of aluminum as well as other metals into the brain and lead to their contribution to such pathological features as neurofibrillar tangles (NFTs).

Inhibition of delta aminolevulinic acid dehydratase activity by aluminum

1. Studies were performed regarding the effects of aluminum chloride and aluminum nitrate in concentrations of 5 mg/kg of body weight on the delta aminolevulinic acid dehydratase activity, iron level and hematological parameters. Wistar rats were exposed to these pollutants for 10, 20, 40 and 80 days. 2. The results demonstrated that aluminum chloride was more toxic than aluminum nitrate and both treatments brought about significant changes in these parameters in Wistar rats bone marrow. 3. The toxic effects of aluminum chloride and aluminum nitrate are manifested by a significant decrease of delta aminolevulinic acid dehydratase activity in the bone marrow of rats. 4. The iron level in bone marrow with aluminum chloride and aluminum nitrate gradually dropped after 10, 20, 40 and 80 days of intoxication. 5. In the peripheral blood a significant decrease in the erythrocyte count, hemoglobin level, hematocrit value and an increase in mean corpuscular hemoglobin (MCH) were also found in experimental animals.

The ability and inability of ATP to stop aluminum from reducing the sodium efflux in unpoisoned barnacle muscle fibers

A study has been made in single barnacle muscle fibers with the object of determining whether ATP is able to protect the resting Na efflux from the effects of injected aluminum (Al) and whether Al is able to reduce or abolish the stimulatory action of ATP on the efflux. The results of the experiments show that neither ATPMg nor ATPNa2 preinjection stops Al from reducing the basal Na efflux in unpoisoned fibers which undergo a large fall (hypersensitive fibers). Preinjection of Al into such fibers reduces or abolishes the stimulatory response of the Na efflux to ATP injection. In less hypersensitive fibers, however, ATPMg is protective. This is also true of ATPNa2 preinjection in both classes of fibers showing stimulation. Injection of a mixture of AlCl3-ATPNa2 into unpoisoned fibers causes less inhibition than AlCl3 injection. The hypothesis that both ATPMg and ATPNa2 are protective is also supported by the results obtained with ouabain-poisoned fibers: (i) Al injection after ATP fails to reverse the stimulatory response to ATP, while ATP injection after Al exerts only a small or no effect. (ii) Mg2+ injection fails to reverse the stimulatory response to Al injection in poisoned fibers. And (iii) Anti-proteolysis agents e.g. leupeptin and pepstatin, upon preinjection, do not alter the kinetic results obtained by injecting Al into unpoisoned and ouabain-poisoned fibers.

Aluminum, altered transcription, and the pathogenesis of Alzheimer's disease

The etiology of some, if not all, cases of Alzheimer's disease is linked to a mutation in the proximal portion of the long arm of chromosome 21∶21q11.2 → 21q22.2. While the functional consequences of the mutation are unknown, we speculate that one consequence of the mutation is loss of the natural barriers and intracellular ligands for aluminum. As a result, aluminum gains access to several brain sites including the nuclear compartment in certain neurons of the central nervous system.Both sporadic and familial Alzheimer's disease are associated with an increased compaction of DNA within chromatin as measured by physical shearing and resistance to digestion by micrococcal nuclease and DNase I. There is also an increase in linker histone Hl(o) content on dinucleosomes released by light (3-5% ASN) micrococcal nuclease digestion, and an increase in the affinity of histone Hl(o) for DNA as measured by a salt elution technique. The change in enzyme accessibility to chromatin also involves the 5' promoter region of at least one physiologically important gene: the gene which codes for the low molecular weight moiety of neurofilament (NF-L). The conformation change involving the 5' regulator region probably reduces transcription because the pool size of the mRNA coding for NF-L is reduced to 14% of age matched control in cerebral grey matter. Reduced transcription may account for many disorders in cellular metabolic processes including the regulation of phosphorylation, calcium homeostasis, free radical metabolism, proteolysis and neurotransmitter metabolism.The experimental evidence indicates that one important toxic action of aluminum in Alzheimer's disease neocortex is to increase the binding of histones, particularly Hl(o), to DNA which results in increased compaction of chromatin and reduced transcription. The supporting evidence includes: (1) A statistically reliable correlation between the aluminum to DNA ratio on intermediate euchromatin and the amount of highly condensed heterochromatin found in a given preparation from Alzheimer affected neocortex (Crapperet al., 1980). (2) A nine-fold increase in aluminum content in Alzheimer's disease in the di- and tri- nucleosome fraction released by light micrococcal nuclease digestion of nuclei from cerebral grey matter compared to age matched controls. Compared to age matched control dinucleosomes, the Alzheimer affected dinucleosomes contain an increased abundance of the linker histone Hl(o) and an increased proportion of DNA containing the promoter region of the gene coding for NF-L. (3) A reduction in abundance to 14% of control mRNA coding for NF-L in Alzheimer affected neocortex (Crapper McLachlanet al., 1988). (4) In vitro evidence that Alzheimer linker histones bind more tightly to DNA than control and that aluminum added to nuclei,in vitro, extracted from normal control brain, enhances DNA-protein binding of Hl and Hl(o) at concentrations found in the Alzheimer affected chromatin (Lukiwet al., 1987). (5) Application of a band retardation assay indicates that aluminum,in vitro, selectively binds human Hl(o) to a 300 bp human ALU DNA fragment from a crude extract of 5% per chloric acid soluble proteins. (6) Aluminum experimentally applied to rabbit CNS induces a marked reduction in NF-L mRNA in anterior horn cells (Mumaet al., 1988). We therefore conclude that aluminum plays a major role in the pathogenesis of Alzheimer's disease. Further understanding of the role of aluminum in Alzheimer's disease requires a detailed investigation of the precise sites of co-ordination of this trivalent metal within chromatin.

Sensitivity of the sodium efflux in single barnacle muscle fibers to the microinjection of aluminum

A study has been made of the behavior of the Na efflux in single muscle fibers from the barnacle, Balanus nubilus, toward the microinjection of AlCl3. The effect of microinjecting AlCl3 is either biphasic with inhibition following transitory stimulation, or monophasic with inhibition occurring promptly and taking about 1 hr to reach a maximum. The magnitude of the inhibition is dose dependent and the minimally effective concentration is 10 mM. This is diluted by the myoplasm by a factor of roughly 100. Fibers injected with 1 M AlCl3 are found to be insensitive to 10(-4) M ouabain, whereas fibers injected with 0.5 M AlCl3 show a further fall in Na efflux, which is smaller than that seen in control fibers. The response of the ouabain-insensitive Na efflux to the injection of 0.5 M AlCl3 is biphasic: stimulation is followed by inhibition. The stimulatory phase is largely dependent on the presence of external Ca2+ and is reversed by the sudden omission of Ca2+ from the bathing medium. Fibers also injected with 0.5 M AlCl3 show a marked reduction in the response of the Na efflux to high external K. Injection of ATPMg before or after the injection of AlCl3 fails in most instances to abolish or reverse the inhibitory effect. By contrast, fibers preinjected with deferoxamine show little or no effect following the injection of AlCl3. However, external application of deferoxamine is ineffective.

Aluminum increases agonist-stimulated cyclic AMP production in rat cerebral cortical slices

The effects of AlCl3 on basal and stimulated cyclic AMP production in rat cerebral cortical slices were studied. AlCl3 (10-250 microM) had no effect on the cyclic AMP concentration in the absence of drugs that stimulate the synthesis of cyclic AMP. 2-Chloroadenosine (25-200 microM) significantly stimulated the synthesis of cyclic AMP in a concentration-dependent manner, and AlCl3 significantly potentiated this response at 50 and 100 microM 2-chloroadenosine. This effect of AlCl3 was dependent on preexposure of the slices to AlCl3 before addition of the agonist. The potentiation by AlCl3 of the 2-chloroadenosine-induced increase in cyclic AMP level was concentration dependent, with significant enhancement by 100 (142% of the control) and 250 (150% of the control) microM AlCl3. Lower concentrations of AlCl3 had no significant effect on the production of cyclic AMP stimulated by 2-chloroadenosine. AlCl3 also potentiated the isoproterenol-induced increase in cyclic AMP production. Forskolin-induced production of cyclic AMP was unaltered by the presence of AlCl3. These results demonstrate that AlCl3 can potentiate agonist-stimulated cyclic AMP production in a whole-cell brain preparation without the addition of fluoride. This may account for the previously reported aluminum-induced increase in cyclic AMP concentrations in rat brain in vivo.

The effects of aluminum on agonist-induced alterations in cyclic AMP and cyclic GMP concentrations in rat brain regions in vivo

Aluminum administered intracerebroventricularly (icv) (1 mumol) caused a significant decrease in cyclic GMP in the cortex after 3 days and a significant increase in cyclic AMP in the cortex after 14 days. Pilocarpine administration to untreated rats elevated cyclic AMP and cyclic GMP levels in specific brain regions. These pilocarpine-induced increases in the cyclic nucleotide concentrations were significantly attenuated in rats that had been treated with aluminum 14 days previously. Isoproterenol administration to control rats did not alter cyclic AMP concentrations; however, cyclic AMP concentrations were significantly reduced in the cortex of aluminum-treated animals after isoproterenol administration. Apomorphine elevated cyclic GMP concentrations in the cerebellum, hippocampus, and striatum of naive rats. This apomorphine-induced elevation in cyclic GMP concentrations was significantly potentiated in aluminum-treated rats. These results indicate that: (1) cyclic AMP synthesis in the cortex is most sensitive to aluminum; (2) agonist-stimulated changes in cyclic nucleotide concentrations can be altered by pretreatment with aluminum; (3) effects of aluminum persist for at least 2 weeks after central administration; and (4) modulation of the metabolism of cyclic nucleotides may play a role in the neurotoxic effects of aluminum.

Effects of iron-limitation of Escherichia coli on growth, the respiratory chains and gallium uptake

The effects of iron limitation on growth, the composition and function of the respiratory chains, and gallium uptake in Escherichia coli have been studied. Decreasing the iron concentration in a defined medium using Chelex resin gave lower growth yields in both continuous culture and prolonged batch culture. In the former, iron-limited (entering [Fe] less than or equal to 2.0 microM) cells exhibited diminished respiration rates, respiration-driven proton translocation quotients, and levels of non-haem iron and cytochromes. The cellular concentration of haemoprotein b-590 (a cytochrome alpha 1-like hydroperoxidase) decreased 20-fold on iron limitation, whilst a CO-binding pigment with an absorption maximum in the dithionite-treated form near 500 nm appeared. Gallium(III) (9 microM) added to iron-limited, but not iron-sufficient, cultures diminished growth yields further; cells grown with low entering concentrations of iron took up less gallium than iron-sufficient cells. These results are attributed to the interference by gallium(III) with siderophore-mediated metal uptake. Gallium also stimulated iron uptake and was itself accumulated by iron-sufficient cells, suggesting that gallium(III) also affects the iron transport system(s) of low affinity.

Age related decline in aluminum-activated human platelet adenylate cyclase: post-receptor changes in cyclic AMP second messenger signal amplification in normal aging and dementia of the Alzheimer type

Low, micromolar concentrations of aluminum (in the presence of NaF) were shown to strongly activate human platelet adenylate cyclase and provided a useful probe for evaluating cyclic AMP second messenger function distal to the receptor: The effect of normal aging and disease state on second messenger activity in man was studied by measurements of the aluminum-activated enzyme. A significant decline in aluminum-stimulated platelet adenylate cyclase activity in older, healthy subjects was observed. An age-associated decline in NaF-stimulated cyclic AMP synthesis was also demonstrated for normal, non-demented subjects. These findings suggest an age-associated lesion at the level of the guanine nucleotide regulatory protein/catalytic subunit of the adenylate cyclase complex. However, for patients with Alzheimer's disease no such decline in platelet adenylate cyclase activity was detected, and increased sensitivity to both aluminum and NaF was demonstrated.

Energy metabolism and its regulation in the adult liver fluke Fasciola hepatica

The adult liver fluke,Fasciola hepatica, inhabits the bile duct of its final host, usually cattle or sheep. The veterinary aspects of infection withF. hepaticacan represent a major problem and consequently fascioliasis can have serious economic effects. As recently as 1972 the loss in revenue due to liver fluke infestations in the UK was estimated at an incredible £50 million per annum (Coles, 1975). Not only canF. hepaticainfect cattle and sheep, but also outbreaks of human disease have been reported. The last serious outbreak in Britain was in 1968 when at least 49 cases were identified (Ashton, Boardman, D'Sa, Everall & Houghton, 1970; Hardman, Jones & Davies, 1970).

Forskolin activation of serotonin-stimulated adenylate cyclase in the liver fluke Fasciola hepatica

Properties of forskolin activation of adenylate cyclase in the liver fluke Fasciola hepatica are described. Forskolin stimulated adenylate cyclase activity in cell-free fluke particles to levels more than 30-fold above the basal rate. This activation was not dependent on guanine nucleotides and, upon washing of the particles, was rapidly reversed. Forskolin potentiated the activation of adenylate cyclase by serotonin (5-HT) and lysergic acid diethylamide (LSD), resulting in both an increase in the maximal level of enzyme activity and a decrease in the apparent activation constant (KA). The 5-HT antagonist 2-bromo-LSD did not inhibit enzyme activation by forskolin. Furthermore, forskolin had no effect on specific [3H]LSD binding to fluke particles. Activation of adenylate cyclase by sodium fluoride or guanine nucleotides was modified in a complex manner by forskolin with both stimulatory and inhibitory effects present. The results suggest that forskolin does not interact directly with the 5-HT receptor coupled to adenylate cyclase. Instead, it appears that forskolin effects are, at least in part, due to its ability to alter the interaction between the regulatory and catalytic components of adenylate cyclase. Incubation of intact flukes with forskolin increased their cAMP levels 2- to 3-fold. The concentration dependence of this response was similar to that for forskolin activation of adenylate cyclase in fluke particles, with 300 microM forskolin giving the maximum response. Forskolin and other agents that increased fluke cAMP levels also stimulated fluke motility.