ISSN:0098-4108    

DOI:10.1080/713851046

出版商:Informa UK Ltd    

年代:1996

数据来源: Taylor

ISSN:0098-4108    

DOI:10.1080/713851038

出版商:Informa UK Ltd    

年代:1996

数据来源: Taylor

ISSN:0098-4108    

DOI:10.1080/009841096161041

出版商:Informa UK Ltd    

年代:1996

数据来源: Taylor

摘要:

A wide range of toxic effects of aluminum (Al) have been demonstrated in plants and aquatic animals in nature, in experimental animals by several routes of exposure, and under different clinical conditions in humans. Aluminum toxicity is a major problem in agriculture, affecting perhaps as much as 40% of arable soils in the world. In fresh waters acidified by acid rain, Al toxicity has led to fish extinction. Aluminum is a very potent neurotoxicant. In humans with chronic renal failure on dialysis, Al causes encephalopathy, osteomalacia, and anemia. There are also reports of such effects in certain patient groups without renal failure. Subtle neurocognitive and psychomotor effects and electroencephalograph (EEG) abnormalities have been reported at plasma Al levels as low as 50 mug/L. Infants could be particularly susceptible to Al accumulation and toxicity, reduced renal function being one contributory cause. Recent reports clearly show that Al accumulation occurs in the tissues of workers with long-term occupational exposure to Al dusts or fumes, and also indicate that such exposure may cause subtle neurological effects. Increased efforts should be directed toward defining the full range of potentially harmful effects in humans. To this end, multidisciplinary collaborative research efforts are encouraged, involving scientists from many different specialities. Emphasis should be placed on increasing our understanding of the chemistry of Al in biological systems, and on determining the cellular and molecular mechanisms of Al toxicity.

ISSN:0098-4108    

DOI:10.1080/009841096161050

出版商:Informa UK Ltd    

年代:1996

数据来源: Taylor

摘要:

As a "hard" trivalent metal ion, Al 3+ binds strongly to oxygen-donor ligands such as citrate and phosphate. The aqueous coordination chemistry of Al is complicated by the tendency of many Al complexes to hydrolyze and form polynuclear species, many of which are sparingly soluble. Thus there is considerable variation among the Al stability constants reported for several important ligands. The complexity in the aqueous chemistry of Al has also affected Al toxicity studies, which have often utilized poorly characterized Al stock solutions. Serum fractionation studies show that most Al is protein bound, primarily to the serum iron transport protein transferrin. Albumin appears to play little, if any, role in serum transport. There is little agreement as to the speciation of the remaining low-molecular-mass fraction of serum Al. The lability of the Al 3+ ion precludes the simple separation and identification of individual Al complexes. Computational methods are available for detailed computer calculations of the Al speciation in serum, but efforts in this area have been severely hampered by the uncertainties regarding the stability constants of the low molecular mass Al complexes with citrate, phosphate, and hydroxide. Specific recommendations for further research on Al speciation include: (1) Determine more accurate Al stability constants with critical low molecular mass ligands such as citrate and phosphate; (2) supplement traditional potentiometric studies on Al complexes with data from other techniques such as 27Al-NMR and accelerator mass spectrometry with 26Al; (3) develop new methods for generating reliable linear free energy relationships for Al complexation; (4) determine equilibrium and rate constants for Al binding to transferrin at 37 C; (5) confirm the possible formation of low-molecular-mass Al-protein complexes following desferrioxamine therapy; (6) continue research efforts to incorporate kinetic considerations into the present equilibrium speciation calculations; (7) improve methods for preparing chemically well-defined stock solutions for toxicological studies; (8) incorporate more detailed speciation data into studies on Al toxicity and pharmacokinetics; and (9) incorporate more detailed speciation data into future epidemiological studies on the relationship between Al toxicity and various water quality parameters.

ISSN:0098-4108    

DOI:10.1080/009841096161069

出版商:Informa UK Ltd    

年代:1996

数据来源: Taylor

摘要:

In this study of the toxicokinetics of aluminum we have examined some of the fundamental issues that currently define our understanding of the toxicology of aluminum in humans. There is a vast literature on this subject, and it was not our aim to review this literature but to use it to develop our understanding of the toxicokinetics of aluminum and to identify critical and unresolved issues related to its toxicity. In undertaking this task we have chosen to define the term toxicokinetics to encompass those factors that influence both the lability of aluminum in a body and the sites at which aluminum is known to accumulate, with or without consequent biological effect. We have approached our objective from the classical pharmacological approach of ADME: the absorption, distribution, metabolism, and excretion of aluminum. This approach was successful in identifying several key deficits in our understanding of aluminum toxicokinetics. For example, we need to determine the mechanisms by which aluminum crosses epithelia, such as those of the gastrointestinal tract and the central nervous system, and how these mechanisms influence both the subsequent transport and fate of the absorbed aluminum and the concomitant nature and severity of the biological response to the accumulation of aluminum. Our hope in highlighting these unresolved issues (summarized in Table 1) is that they will be addressed in future research.

ISSN:0098-4108    

DOI:10.1080/009841096161078

出版商:Informa UK Ltd    

年代:1996

数据来源: Taylor

摘要:

Information concerning developmental aluminum (Al) toxicity is available from clinical studies and from animal testing. An Al toxicity syndrome including encephalopathy, osteomalacia, and anemia has been reported in uremic children receiving dialysis. In addition, some components of the syndrome, particularly osteomalacia, have been reported in nondialyzed uremic children receiving Al-based phosphate binders, nonuremic infants receiving parenteral nutrition with Al-containing fluids, and nonuremic infants given high doses of Al antacids. The number of children in clinical populations that are at risk of Al toxicity is not known and needs to be determined. Work in animal models (rats, mice, and rabbits) demonstrates that Al is distributed transplacentally and is present in milk. Oral Al administration during pregnancy produces a syndrome including growth retardation, delayed ossification, and malformations at doses that also lead to reduced maternal weight gain. The severity of the effects is highly dependent on the form of Al administered. In the postnatal period, reduced pup weight gain and effects on neuromotor development have been described as a result of developmental exposures. The significance of these findings for human health requires better understanding of the amount and bioavailability of Al in food, drinking water, and medications and from sources unique to infants and children such as breast milk, soil ingestion, and medications used specifically by pregnant women and children. We also need a better understanding of the unique biological actions of Al that may occur during developmental periods, and unique aspects of the developing organism that make it more or less susceptible to Al toxicity.

ISSN:0098-4108    

DOI:10.1080/009841096161087

出版商:Informa UK Ltd    

年代:1996

数据来源: Taylor

摘要:

Regardless of the host, the route of administration, or the speciation, aluminum is a potent neurotoxicant. In the young adult or developmentally mature host, the neuronal response to Al exposure can be dichotomized on morphological grounds. In one, intraneuronal neurofilamentous aggregates are formed, whereas in the other, significant neurochemical and neurophysiological perturbations are induced without neurofilamentous aggregate formation. Evidence is presented that the induction of neurofilamentous aggregates is a consequence of alterations in the posttranslational processing of neurofilament (NF), particularly with regard to phosphorylation state. Although Al has been reported to impact on gene expression, this does not appear to be critical to the induction of cytoskeletal pathology. In hosts responding to Al exposure without the induction of cytoskeletal pathology, impairments in glucose utilization, agonist-stimulated inositol phosphate accumulation, free radical-mediated cytotoxicity, lipid peroxidation, reduced cholinergic function, and altered protein phosphorylation have been described. The extent to which these neurochemical modifications correlate with the induction of a characteristic neurobehavioral state is unknown. In addition to these paradigms, Al is toxic in the immediate postnatal interval. Whether unique mechanisms of toxicity are involved during development remains to be determined. In this article, the mechanisms of Al neurotoxicity are reviewed and recommendations are put forth with regard to future research. Primary among these is the determination of the molecular site of Al toxicity, and whether this is based on Al substitution for divalent metals in a number of biological processes. Encompassed within this is the need to further understand the genesis of host- and developmental-specific responses.

ISSN:0098-4108    

DOI:10.1080/009841096161096

出版商:Informa UK Ltd    

年代:1996

数据来源: Taylor

摘要:

Aluminum (Al) is unquestionably neurotoxic in both experimental animals and certain human diseases. Minute quantities injected intracerebrally into rabbits will induce severe neurological symptoms and neuropathological features of neurodegeneration. Hyperaluminemia often develops in patients with renal failure being treated with intermittent hemodialysis on a chronic basis, and in severe cases results in an encephalopathy. Uremic adults and premature infants not on dialysis treatment also can develop encephalopathy due to Al toxicity, as is the case when large amounts of alum are used as a urinary bladder irrigant. There are many other examples of Al-induced neurotoxicity; however, the question as to whether Al presents a health hazard to humans as a contributing factor to Alzheimer's disease is still the subject of debate. Several lines of evidence are presented that have formed the basis of the debate concerning the possible pathogenic role for Al in Alzheimer's disease. Important evidence for an Al-Alzheimer's causal relationship is the observation by laser microprobe mass analysis (LMMS) of the presence of Al in neurofibrillary tangles, although there are conflicting data on the extent of the Al deposition. The relatively poor sensitivity of some of the analytical instruments available for these challenging in situ microanalyses could explain the discrepant results, although LMMS and perhaps secondary ion mass spectrometry (SIMS) appear to be sufficiently sensitive. Harmonization of the techniques is an essential next step. There is new evidence that exposure to Al from drinking water might result in cognitive impairment and an increased incidence of Alzheimer's disease. However, these epidemiological studies have inherent problems that must be scrutinized to determine if an association really does exist. An understanding of a possible enhanced bioavailability of Al in this type of exposure, versus other exposures such as antacid intake or industrial exposure, needs to be considered and explored. There has been one promising clinical trial of the treatment of Alzheimer's disease patients with the Al chelator desferrioxamine (DFO). Further studies are needed, and if confirmation is forthcoming then such data could also support an Al-Alzheimer's disease link as well as suggesting that DFO offers potential as a therapeutic agent. The possibility that iron might be the offending agent needs to be considered since DFO is a very strong iron chelator. The significance of Al-induced neurofibrillary degeneration in experimental animals should be assessed especially in light of new data showing that this model exhibits abnormally phosphorylated tau protein structures in the neuronal perikarya. Thus the key questions that must be answered before it can be asserted that Al possesses a causal relationship to Alzheimer's disease, are as follows and are addressed in this present discussion: (1) Are there elevations of the concentration of Al in the brains of Alzheimer's disease patients? (2) Is there a relationship between environmental exposure to Al, particularly in drinking water, and an increased risk of Alzheimer's disease? (3) Is treatment with DFO a potentially useful therapeutic approach and to what extent might beneficial effects of DFO implicate Al in the etiology of Alzheimer's disease? (4) Are there similarities between the experimental animal studies and Alzheimer's disease particularly in the development of abnormal forms of tau seen in neurofibrillary tangles? (5) Does Al promote the deposition of the A peptide in Alzheimer's disease? (6) Does hyperaluminemia associated with long-term hemodialysis treatment induce neurofibrillary degeneration? If the answer to each of these six questions is yes, then does this assert that Al possesses a causal relationship to Alzheimer's disease? On the other hand, must all six be met to be able to make this assertion? It is possible that other factors may contribute to Al-induced neurotoxicity, and therefore increased Al accumulation may not accompany neurotoxicity in the presence of these other factors.

ISSN:0098-4108    

DOI:10.1080/009841096161104

出版商:Informa UK Ltd    

年代:1996

数据来源: Taylor

摘要:

A review of the literature of aluminum ( Al) levels in biological samples, particularly Alzheimer's disease (AD) brain, reveals a lack of interlaboratory agreement at both the bulk and microprobe levels. One possible reason for this controversy may be the methods chosen for quantitation and standardization. Currently, the major problem affecting quantitation of Al at the bulk level is the lack of low-Al-concentration, matrix-matched certified standards. Although a number of certified aluminum bulk standards are available, most do not match well in matrix with the samples of interest. A similar situation exists for microprobe standards in which commercially available pure metal foils and thin films of materials, such as metal oxides, are available but again do not match well in matrix. A review of the current status of quantitation of Al levels in biological analyses at the bulk and microprobe level is presented. Future directions to develop standards include the submission of currently used microprobe standards to a central laboratory for critical analysis and selection of the optimum standard, followed by establishment of interlaboratory and intertechnique comparisons. Other future directions include the adaptation of a standard protocol for the selection of tissue for analysis and criteria for data rejection, as well as the development of a standard system for data normalization and reporting.

ISSN:0098-4108    

DOI:10.1080/009841096161113

出版商:Informa UK Ltd    

年代:1996

数据来源: Taylor