- Email: [email protected]
Author's response to commentaries
556
McI~ACH I..A N
6. Garruto, R. M., C. Swyt, C. E. Fiori, R. Yanagihara and D. C. Gajdusek. Intraneuronal deposition of calcium and aluminum in amyotrophic lateral sclerosis of Guam. Lancet II: 1353, 1985. 7. Garruto, R. M., C. Swyt, R. Yanagihara, C. E. Fiori and D. C. Gajdusek. lntraneuronal colocalization of silicon with calcium and aluminum in amyotrophic lateral sclerosis and parkinsonism with dementia of Guam. N Engl .I Med 315:711-7i2. 1986. 8. Garruto, R. M., R. Yanagihara, D. C. Gajdusek and D. M. Arion. Concentrations of heavy metals and essential minerals in garden soil and drinking water in the Western Pacific. In: Amyotrophic Lateral Sclerosis in Asia and Oceania. edited by K. M. Chen and Y. Yase. Taipe: National Taiwan University Press, 1984, pp. 265-329. 9. Glenner, G. C. and C. V. Wong. Alzheimer's disease and Down's syndrome: sharing of a unique cerebrovascular amyloid fibril protein. Bioehem Biophys Res Comman 122:1131-1135, 1984. 10. Goldgaber, D., M. Lerman, W. McBride, U. Saffiotti and D. C. Gaidusek. Isolation, characterization and chromosomal localization of cDNA clones coding for the precursor of the amyloid of brain in Alzheimer disease, Down's syndrome, and aging. Proe Natl Acad Sei USA, in press, 1987. 11. Guiroy, D. C., M. Miyazaki, G. Multhaup, P. Fischer, R. M. Garruto, K. Beyreuther, C. Masters, G. Simms, C. J. Gibbs, Jr. and D. C. Gajdusek. Amyloids of neurofibrillary tangles of Guamanian parkinsonism-dementia and Alzheimer's disease share identical amino acid sequence. Proc Natl Aead Sci USA, in press, 1987. 12. Iler, R. K. Hydrogen-bond complexes of silica with organic compounds. In: Biochemistry o.f SiHeon and Related Problems, edited by G. Bendz and I. Lindqvist. New York: Plenum, 1985, pp. 53-76.
13. Masters, C. L., G. Multhaup, G. Simms, J. Pottigiesser, R. N. Martins and K. Beyreuther. Neuronal origin of a cerebral amyloid: neurofibrillary tangles of Alzheimer's disease contain the same protein as the amyloid of plaque cores and blood re> sels. EMBO ,I 4: 2757-2763, 1985. 14. Perl, D., D. C. Gajdusek, R. M. Garrout, R. T. Yanagihara and C. J. Gibbs, Jr. lntracellular aluminum (AI) accumulation in neurofibrillary tangle (NFT)-bearing neurons in Guamanian A LS and parkinsonism-dementia (PD). Abstract number D1-13 in Abstracts of the Ninth International Congress of Neuropathology, Vienna, September 5-10. p. 31, 1982. 15. Perl. D. P., D. C. Gajdusek, R. M. Garruto, R. T. Yanagihara and C. J. Gibbs, Jr. Intraneuronal aluminum accumulation in amyotrophic lateral sclerosis and parkinsonism-dementia of Guam. Science 217: 1053-1055, 1982. 16. Svedmyr, A., S. K. Shankar, M. Miyazaki, R. Yanagihara and D. C. Gajdusek. In program: Abstracts of the American Academy of Neurology, April 5-11, New York, NY. 17. Weis, A. Replication and evolution in inorganic systems. An,,,ew Uhem [En~,/] 20: 850-860, 1981. 18. Yoshimasu, F., M. Yasui. H. Yoshida, S. Yoshida, Y. Lebayashi, Y. Yase, D. C. Gajdusek and K. M. Chen. Aluminum in Alzheimer's disease in Japan and parkinsonismdementia in Guam. XII World Congress of Neurology. Abstract 15.07.02, 1985.
EDITORIAL NOTE The preceding commentary arrived too late to be reviewed by Dr. McLachlan and was therefore not addressed in the following author's response to commentaries.
Author's Response to Commentaries D. R. C R A P P E R
McLACHLAN
D e p a r t m e n t o f P h y s i o l o g y , 3318 M e d i c a l S c i e n c e s Building University o f Toronto, T o r o n t o , C a n a d a
D E S P I T E the recent increase in k n o w l e d g e about aluminum neurotoxicity and A l z h e i m e r ' s disease, each of the c o m m e n taries e m p h a s i z e s that e v i d e n c e for a cause and effect relation b e t w e e n aluminum and any o f the signs, s y m p t o m s , morphological or m o l e c u l a r changes of A l z h e i m e r ' s disease is wanting. N e v e r t h e l e s s , most o f the c o m m e n t a r i e s have e x p r e s s e d the need to evaluate more fully the significance of the p r e s e n c e of this highly toxic agent in neurons, blood vessels and other structures in a disease as devastating and obscure as A l z h e i m e r ' s disease. S e v e r a l of the c o m m e n taries have indicated specific areas of investigation which should be addressed i m m e d i a t e l y in order to assess further the i n v o l v e m e n t o f aluminum in the pathogenesis o f the disease. F o r instance, the c o m m e n t a r i e s o f Gambetti, and Ghetti and Bugiani e m p h a s i z e the need to e x a m i n e further the effects o f aluminum upon cytoskeletal phosphorylation, side arm linkages and neurofilament motility. H o w e v e r , experiments which will convincingly e v a l u a t e a cause and effect relation of aluminum in A l z h e i m e r ' s disease have not been e x e c u t e d or p r o p o s e d by any o f the workers in the field, perhaps because current technology is wanting.
Technological limitations must be c i r c u m v e n t e d in order to address several of the important issues raised by Drs. Pettegrew and Perl. Present day imaging techniques detect aluminum localized to regions o f high concentration. Instruments capable of detecting the entire range of biological concentrations of aluminum and other elements in control and pathological nervous tissues must be developed. The reliable detection of aluminum within structures of normal brain must be a c h i e v e d before the e x a c t temporal relation can be evaluated b e t w e e n the accumulation of abnormal concentrations of aluminum in the brain and the onset o f functional and morphological changes associated with A l z h e i m e r ' s disease. Furthermore, if aluminum alters gene expression of a single c o p y gene by an action upon a promoter, a single aluminum atom at a critical site may be sufficient to alter m e s s e n g e r R N A production within the affected cell. E x p e r i m e n t s with sufficient resolution to test this class of hypothesis may be limited by current technology. In response to a point m a d e by Dr. Gambetti, our experiments designed to measure m R N A c o n t e n t for the 68 kDa neurofilament subunit in the rabbit aluminum induced
RESPONSE TO COMMENTARIES
557
encephalopathy failed to reveal a significant reduction in the early post injection period. However, by day 10 post injection messenger content for NF68, and several other cytoskeletal messengers, was significantly reduced. Although bundles of neurofibrillary tangles may occasionally be found free of membranes, Dr. Perl emphasizes the important fact that neurons with neurofibrillary degeneration are not necessarily "~dying" cells. Neurons with neurofibrillary degeneration may have intact membranes and morphologically normal intracellular organelles and synapses. The observation that elements other than calcium are not increased in the affected neurons argues against non-specific neuron damage as the cause of aluminum accumulation. The cellular mechanisms responsible for calcium homeostasis and aluminum turnover in neurons must be studied in greater detail to adequately explain the observed findings. Dr. Alfrey argues that the slight increase in brain aluminum content in Alzheimer's disease is less than that required to produce dialysis encephalopathy and therefore of little importance in the pathogenesis of the disease. Indeed, bulk tissue measurements of 10 to 20 mg dry weight reveal that about 3(FX of samples obtained from cerebral cortex exceed the mean plus three standard deviations of the mean for age matched control brain samples. However, Dr. Perl's recent quantitative measures indicate foci of aluminum with concentrations of 100 to 400 bLg/g. High concentration of aluminum in discrete intracellular organelles is likely to be a more important determinant of toxicity than measurements of total tissue content, especially when the density of neurofibrillary degeneration rarely exceeds 2% of cells in cerebral cortex. It is impossible to dismiss such high, localized, aluminum concentrations in intact neurons as subthreshold for toxic effects. Elevated aluminum concentrations in Alzheimer's disease occur in brain of individuals who have not received parental fluids in the terminal illness and in brain biopsy specimens obtained early in the natural history of Alzheimer's disease. These observations exclude the possibility that aluminum contaminated parental fluids given during the terminal hospitalization account for elevated brain aluminum in Alzheimer's disease.
Dr. Wisniewski and his group have made major contributions to the study of both aluminum toxicity and Alzheimer's disease. His demand for definitive experiments to precisely establish the role of aluminum in Alzheimer's disease must be heeded. In examining the molecular events underlying AIzheimer's disease, the " A N D " gate analogy of Dr. Khachaturian is a particularly useful concept. In an AND gate, a discrete event has to take place at each of the inputs of the gate but the timing of the events at the various gates may vary provided that the effect lingers. This concept, applied to Alzheimer's disease, should encourage research into persistent substances like aluminum, especially when they are associated with DNA and the genetic apparatus. The commentary of Dr. Carlisle indicates that aluminum may be an essential element, although she and Dr. Marquis emphasize that chronic oral exposure of aluminum may be related to toxicity. Dr. Jope rightly points out that rats do not develop a progressive encephalopathy with neurofibrillary degeneration in response to aluminum similar to that seen in rabbits and cats, but do exhibit toxic manifestations and are useful in the study of aluminum toxicity. AIzheimer's disease is a relentlessly progressive lethal brain disease for which no treatment is available to arrest or prevent the deterioration. Despite incomplete understanding of the exact role of aluminum in Alzheimer's disease, Dr. Liss and his collaborators have undertaken to test the hypothesis that the reduction in post prandial serum aluminum concentration will alter the clinical course of the illness. Perhaps the most important .justification for the intensive study of aluminum in Alzheimer's disease is that this common environmental element could be manipulated through environmental, dietary and chemotherapeutic intervention for individuals with the disease or at risk for the disease. Ultimately. humanitarian and social considerations require that the exact role of aluminum in Alzheimer's disease be delineated. When the consequences of aluminum accumulation in Alzheimer's disease are known at the level of atomic and molecular interactions we will also have advanced far toward the more important goal, that of understanding the molecular biology of Alzheimer's disease.
Letters to the Editor We encourage our readers to respond to this review and associated peer commentaries in the form of formal "Letters to the Editor." Relatively short letters with a specific point or two are most appropriate. In all cases, the author of the original review or commentary will be given an opportunity to respond to the letter.
McI~ACH I..A N
6. Garruto, R. M., C. Swyt, C. E. Fiori, R. Yanagihara and D. C. Gajdusek. Intraneuronal deposition of calcium and aluminum in amyotrophic lateral sclerosis of Guam. Lancet II: 1353, 1985. 7. Garruto, R. M., C. Swyt, R. Yanagihara, C. E. Fiori and D. C. Gajdusek. lntraneuronal colocalization of silicon with calcium and aluminum in amyotrophic lateral sclerosis and parkinsonism with dementia of Guam. N Engl .I Med 315:711-7i2. 1986. 8. Garruto, R. M., R. Yanagihara, D. C. Gajdusek and D. M. Arion. Concentrations of heavy metals and essential minerals in garden soil and drinking water in the Western Pacific. In: Amyotrophic Lateral Sclerosis in Asia and Oceania. edited by K. M. Chen and Y. Yase. Taipe: National Taiwan University Press, 1984, pp. 265-329. 9. Glenner, G. C. and C. V. Wong. Alzheimer's disease and Down's syndrome: sharing of a unique cerebrovascular amyloid fibril protein. Bioehem Biophys Res Comman 122:1131-1135, 1984. 10. Goldgaber, D., M. Lerman, W. McBride, U. Saffiotti and D. C. Gaidusek. Isolation, characterization and chromosomal localization of cDNA clones coding for the precursor of the amyloid of brain in Alzheimer disease, Down's syndrome, and aging. Proe Natl Acad Sei USA, in press, 1987. 11. Guiroy, D. C., M. Miyazaki, G. Multhaup, P. Fischer, R. M. Garruto, K. Beyreuther, C. Masters, G. Simms, C. J. Gibbs, Jr. and D. C. Gajdusek. Amyloids of neurofibrillary tangles of Guamanian parkinsonism-dementia and Alzheimer's disease share identical amino acid sequence. Proc Natl Aead Sci USA, in press, 1987. 12. Iler, R. K. Hydrogen-bond complexes of silica with organic compounds. In: Biochemistry o.f SiHeon and Related Problems, edited by G. Bendz and I. Lindqvist. New York: Plenum, 1985, pp. 53-76.
13. Masters, C. L., G. Multhaup, G. Simms, J. Pottigiesser, R. N. Martins and K. Beyreuther. Neuronal origin of a cerebral amyloid: neurofibrillary tangles of Alzheimer's disease contain the same protein as the amyloid of plaque cores and blood re> sels. EMBO ,I 4: 2757-2763, 1985. 14. Perl, D., D. C. Gajdusek, R. M. Garrout, R. T. Yanagihara and C. J. Gibbs, Jr. lntracellular aluminum (AI) accumulation in neurofibrillary tangle (NFT)-bearing neurons in Guamanian A LS and parkinsonism-dementia (PD). Abstract number D1-13 in Abstracts of the Ninth International Congress of Neuropathology, Vienna, September 5-10. p. 31, 1982. 15. Perl. D. P., D. C. Gajdusek, R. M. Garruto, R. T. Yanagihara and C. J. Gibbs, Jr. Intraneuronal aluminum accumulation in amyotrophic lateral sclerosis and parkinsonism-dementia of Guam. Science 217: 1053-1055, 1982. 16. Svedmyr, A., S. K. Shankar, M. Miyazaki, R. Yanagihara and D. C. Gajdusek. In program: Abstracts of the American Academy of Neurology, April 5-11, New York, NY. 17. Weis, A. Replication and evolution in inorganic systems. An,,,ew Uhem [En~,/] 20: 850-860, 1981. 18. Yoshimasu, F., M. Yasui. H. Yoshida, S. Yoshida, Y. Lebayashi, Y. Yase, D. C. Gajdusek and K. M. Chen. Aluminum in Alzheimer's disease in Japan and parkinsonismdementia in Guam. XII World Congress of Neurology. Abstract 15.07.02, 1985.
EDITORIAL NOTE The preceding commentary arrived too late to be reviewed by Dr. McLachlan and was therefore not addressed in the following author's response to commentaries.
Author's Response to Commentaries D. R. C R A P P E R
McLACHLAN
D e p a r t m e n t o f P h y s i o l o g y , 3318 M e d i c a l S c i e n c e s Building University o f Toronto, T o r o n t o , C a n a d a
D E S P I T E the recent increase in k n o w l e d g e about aluminum neurotoxicity and A l z h e i m e r ' s disease, each of the c o m m e n taries e m p h a s i z e s that e v i d e n c e for a cause and effect relation b e t w e e n aluminum and any o f the signs, s y m p t o m s , morphological or m o l e c u l a r changes of A l z h e i m e r ' s disease is wanting. N e v e r t h e l e s s , most o f the c o m m e n t a r i e s have e x p r e s s e d the need to evaluate more fully the significance of the p r e s e n c e of this highly toxic agent in neurons, blood vessels and other structures in a disease as devastating and obscure as A l z h e i m e r ' s disease. S e v e r a l of the c o m m e n taries have indicated specific areas of investigation which should be addressed i m m e d i a t e l y in order to assess further the i n v o l v e m e n t o f aluminum in the pathogenesis o f the disease. F o r instance, the c o m m e n t a r i e s o f Gambetti, and Ghetti and Bugiani e m p h a s i z e the need to e x a m i n e further the effects o f aluminum upon cytoskeletal phosphorylation, side arm linkages and neurofilament motility. H o w e v e r , experiments which will convincingly e v a l u a t e a cause and effect relation of aluminum in A l z h e i m e r ' s disease have not been e x e c u t e d or p r o p o s e d by any o f the workers in the field, perhaps because current technology is wanting.
Technological limitations must be c i r c u m v e n t e d in order to address several of the important issues raised by Drs. Pettegrew and Perl. Present day imaging techniques detect aluminum localized to regions o f high concentration. Instruments capable of detecting the entire range of biological concentrations of aluminum and other elements in control and pathological nervous tissues must be developed. The reliable detection of aluminum within structures of normal brain must be a c h i e v e d before the e x a c t temporal relation can be evaluated b e t w e e n the accumulation of abnormal concentrations of aluminum in the brain and the onset o f functional and morphological changes associated with A l z h e i m e r ' s disease. Furthermore, if aluminum alters gene expression of a single c o p y gene by an action upon a promoter, a single aluminum atom at a critical site may be sufficient to alter m e s s e n g e r R N A production within the affected cell. E x p e r i m e n t s with sufficient resolution to test this class of hypothesis may be limited by current technology. In response to a point m a d e by Dr. Gambetti, our experiments designed to measure m R N A c o n t e n t for the 68 kDa neurofilament subunit in the rabbit aluminum induced
RESPONSE TO COMMENTARIES
557
encephalopathy failed to reveal a significant reduction in the early post injection period. However, by day 10 post injection messenger content for NF68, and several other cytoskeletal messengers, was significantly reduced. Although bundles of neurofibrillary tangles may occasionally be found free of membranes, Dr. Perl emphasizes the important fact that neurons with neurofibrillary degeneration are not necessarily "~dying" cells. Neurons with neurofibrillary degeneration may have intact membranes and morphologically normal intracellular organelles and synapses. The observation that elements other than calcium are not increased in the affected neurons argues against non-specific neuron damage as the cause of aluminum accumulation. The cellular mechanisms responsible for calcium homeostasis and aluminum turnover in neurons must be studied in greater detail to adequately explain the observed findings. Dr. Alfrey argues that the slight increase in brain aluminum content in Alzheimer's disease is less than that required to produce dialysis encephalopathy and therefore of little importance in the pathogenesis of the disease. Indeed, bulk tissue measurements of 10 to 20 mg dry weight reveal that about 3(FX of samples obtained from cerebral cortex exceed the mean plus three standard deviations of the mean for age matched control brain samples. However, Dr. Perl's recent quantitative measures indicate foci of aluminum with concentrations of 100 to 400 bLg/g. High concentration of aluminum in discrete intracellular organelles is likely to be a more important determinant of toxicity than measurements of total tissue content, especially when the density of neurofibrillary degeneration rarely exceeds 2% of cells in cerebral cortex. It is impossible to dismiss such high, localized, aluminum concentrations in intact neurons as subthreshold for toxic effects. Elevated aluminum concentrations in Alzheimer's disease occur in brain of individuals who have not received parental fluids in the terminal illness and in brain biopsy specimens obtained early in the natural history of Alzheimer's disease. These observations exclude the possibility that aluminum contaminated parental fluids given during the terminal hospitalization account for elevated brain aluminum in Alzheimer's disease.
Dr. Wisniewski and his group have made major contributions to the study of both aluminum toxicity and Alzheimer's disease. His demand for definitive experiments to precisely establish the role of aluminum in Alzheimer's disease must be heeded. In examining the molecular events underlying AIzheimer's disease, the " A N D " gate analogy of Dr. Khachaturian is a particularly useful concept. In an AND gate, a discrete event has to take place at each of the inputs of the gate but the timing of the events at the various gates may vary provided that the effect lingers. This concept, applied to Alzheimer's disease, should encourage research into persistent substances like aluminum, especially when they are associated with DNA and the genetic apparatus. The commentary of Dr. Carlisle indicates that aluminum may be an essential element, although she and Dr. Marquis emphasize that chronic oral exposure of aluminum may be related to toxicity. Dr. Jope rightly points out that rats do not develop a progressive encephalopathy with neurofibrillary degeneration in response to aluminum similar to that seen in rabbits and cats, but do exhibit toxic manifestations and are useful in the study of aluminum toxicity. AIzheimer's disease is a relentlessly progressive lethal brain disease for which no treatment is available to arrest or prevent the deterioration. Despite incomplete understanding of the exact role of aluminum in Alzheimer's disease, Dr. Liss and his collaborators have undertaken to test the hypothesis that the reduction in post prandial serum aluminum concentration will alter the clinical course of the illness. Perhaps the most important .justification for the intensive study of aluminum in Alzheimer's disease is that this common environmental element could be manipulated through environmental, dietary and chemotherapeutic intervention for individuals with the disease or at risk for the disease. Ultimately. humanitarian and social considerations require that the exact role of aluminum in Alzheimer's disease be delineated. When the consequences of aluminum accumulation in Alzheimer's disease are known at the level of atomic and molecular interactions we will also have advanced far toward the more important goal, that of understanding the molecular biology of Alzheimer's disease.
Letters to the Editor We encourage our readers to respond to this review and associated peer commentaries in the form of formal "Letters to the Editor." Relatively short letters with a specific point or two are most appropriate. In all cases, the author of the original review or commentary will be given an opportunity to respond to the letter.