Radiosensitivity in alzheimer disease and Parkinson disease

Review: Somatic mutations in neurodegeneration

Somatic mutations are postzygotic mutations which may lead to mosaicism, the presence of cells with genetic differences in an organism. Their role in cancer is well established, but detailed investigation in health and other diseases has only been recently possible. This has been empowered by the improvements of sequencing techniques, including single-cell sequencing, which can still be error-prone but is rapidly improving. Mosaicism appears relatively common in the human body, including the normal brain, probably arising in early development, but also potentially during ageing. In this review, we first discuss theoretical considerations and current evidence relevant to somatic mutations in the brain. We present a framework to explain how they may be integrated with current views on neurodegeneration, focusing mainly on sporadic late-onset neurodegenerative diseases (Parkinson's disease, Alzheimer's disease and amyotrophic lateral sclerosis). We review the relevant studies so far, with the first evidence emerging in Alzheimer's in particular. We also discuss the role of mosaicism in inherited neurodegenerative disorders, particularly somatic instability of tandem repeats. We summarize existing views and data to present a model whereby the time of origin and spatial distribution of relevant somatic mutations, combined with any additional risk factors, may partly determine the development and onset age of sporadic neurodegenerative diseases.

Chromatin regulation of DNA damage repair and genome integrity in the central nervous system

With the continued extension of lifespan, aging and age-related diseases have become a major medical challenge to our society. Aging is accompanied by changes in multiple systems. Among these, the aging process in the central nervous system is critically important but very poorly understood. Neurons, as post-mitotic cells, are devoid of replicative associated aging processes, such as senescence and telomere shortening. However, because of the inability to self-replenish, neurons have to withstand challenge from numerous stressors over their lifetime. Many of these stressors can lead to damage of the neurons' DNA. When the accumulation of DNA damage exceeds a neuron's capacity for repair, or when there are deficiencies in DNA repair machinery, genome instability can manifest. The increased mutation load associated with genome instability can lead to neuronal dysfunction and ultimately to neuron degeneration. In this review, we first briefly introduce the sources and types of DNA damage and the relevant repair pathways in the nervous system (summarized in Fig. 1). We then discuss the chromatin regulation of these processes and summarize our understanding of the contribution of genomic instability to neurodegenerative diseases.

Transient neuroprotection by SRY upregulation in dopamine cells following injury in males

Emerging evidence suggest sex-specific regulation of dopamine neurons may underlie susceptibility of males to disorders such as Parkinson's disease (PD). In healthy male dopamine neurons, the Y-chromosome gene product, the sex-determining region on the Y chromosome (SRY) modulates dopamine biosynthesis and motor function. We investigated the regulation and function of SRY in a model of dopamine cell injury. Treatment with the dopaminergic toxin, 6-hydroxydopamine (6-OHDA), significantly elevated SRY mRNA expression (9-fold) in human male dopamine M17 cells. SRY up-regulation occurred via the p-quinone pathway, associated with a 3.5-fold increase in expression of GADD45γ, a DNA damage inducible factor gene and known SRY regulator. In turn, a signaling cascade involving GADD45γ/p38-MAPK/GATA activated the SRY promoter. Knockdown of SRY mRNA in 6-OHDA-treated M17 cells was deleterious, increasing levels of reactive oxygen species (ROS), pro-apoptotic marker PUMA mRNA, and cell injury (+25%, +32% and +34%, respectively). Conversely, ectopic over-expression of SRY in 6-OHDA-treated female SH-SY5Y cells was protective, decreasing ROS, PUMA, and cell injury (-40%, -46%, and -30%, respectively). However, the 6-OHDA-induced increase in SRY expression was diminished with higher concentrations of toxins or with chronic exposure to 6-OHDA. We conclude that SRY upregulation after dopamine cell injury is initially a protective response in males, but diminishes with gradual loss in dopamine cells. We speculate that dysregulation of SRY may contribute the susceptibility of males to PD.

Hexose Transport and Metabolism in Cultured Fibroblasts Derived from Normal and Alzheimer Disease Affected Individuals

The transport and metabolism of glucose was compared in cultured skin fibroblasts derived from normal and Alzheimer disease affected individuals. No significant differences were observed in sugar transport, CO2 production, lactate production, trichloroacetic acid soluble and precipitable material between the test groups. It is concluded that altered glucose uptake or metabolism is not a general characteristic of all Alzheimer disease cultured fibroblasts.

Neuronal NOS inhibitor that reduces oxidative DNA lesions and neuronal sensitivity increases the expression of intact c-fos transcripts after brain injury

In response to oxidative stress, the ischemic brain induces immediate early genes when its nuclear genes contain gene damage. Antioxidant that reduces gene damage also reduces cell death. To study the mechanism of neuronal sensitivity, we investigated the transcription of the c-fos gene after brain injury of the ischemia-reperfusion type using focal cerebral ischemia-reperfusion in Long-Evans hooded rats. We observed a significant (p < 0.01) increase in c-fos mRNA in the ischemic cortex immediately after brain injury. However, the c-fos transcript was sensitive to RNase A protection assay (RPA) upon reperfusion. The transcript became significantly resistant to RPA (42%, p < 0.03) when 3-bromo-7-nitroindazole (25 mg/kg, i.p.), known to abolish nitric oxide, gene damage and neuronal sensitivity, was injected. Our data suggest that neuronal nitric oxide synthase and aberrant mRNA from genes with oxidative damage could be associated with neuronal sensitivity.

Ischemic Neuronal Apoptosis: A View Based on Free Radical-Induced DNA Damage and Repair

Neurons are different from other cells in that they are postmitotic and not replaced after they are lost. The CNS is thus particularly vulnerable to neuronal cell loss from various causes, including ischemic injury. Recent observations show that apoptosis is a common feature in neurons dying of ischemic injury. Free radicals have been implicated in the pathogenesis of ischemic brain injury. Reperfusion after cerebral ischemia is accompanied by excessive free radical formation. Many of these free radicals are reactive oxygen species and cause oxidative damage to DNA. The base-excision repair pathway is believed to repair oxidative DNA damage in the brain after ischemia-reperfusion. We review recent laboratory findings that provide evidence of free radical-induced DNA damage and repair after ischemic injury. The polymerase responsible for replication during base-excision repair, DNA polymerase-β, lacks proofreading activity and is considered error prone. This may lead to the accumulation of DNA damage and genomic instability, probable causes of accelerated neuronal aging. A number of DNA repair genes, including ataxia teleangiectasia, p53, and poly(ADP-ribose) polymerase, are activated after DNA damage. The pathogenetic roles of these genes in ischemia-induced neuronal apoptosis are under active investigation. NEUROSCIENTIST 4:88-95, 1998

Melatonin and N-tert-butyl-alpha-phenylnitrone block 60-Hz magnetic field-induced DNA single and double strand breaks in rat brain cells

In previous research, we have found an increase in DNA single- and double-strand breaks in brain cells of rats after acute exposure (two hours) to a sinusoidal 60-Hz magnetic field. The present experiment was carried out to investigate whether treatment with melatonin and the spin-trap compound N-tert-butyl-alpha-phenylnitrone (PBN) could block the effect of magnetic fields on brain cell DNA. Rats were injected with melatonin (1 mg/kg, sc) or PBN (100 mg/kg, ip) immediately before and after two hours of exposure to a 60-Hz magnetic field at an intensity of 0.5 mT. We found that both drug treatments blocked the magnetic field-induced DNA single- and double-strand breaks in brain cells, as assayed by a microgel electrophoresis method. Since melatonin and PBN are efficient free radical scavengers, these data suggest that free radicals may play a role in magnetic field-induced DNA damage.

Damage, repair, and mutagenesis in nuclear genes after mouse forebrain ischemia-reperfusion

To determine whether oxidative stress after cerebral ischemia-reperfusion affects genetic stability in the brain, we studied mutagenesis after forebrain ischemia-reperfusion in Big Blue transgenic mice (male C57BL/6 strain) containing a reporter lacI gene, which allows detection of mutation frequency. The frequency of mutation in this reporter lacI gene increased from 1.5 to 7.7 (per 100,000) in cortical DNA after 30 min of forebrain ischemia and 8 hr of reperfusion and remained elevated at 24 hr reperfusion. Eight DNA lesions that are characteristic of DNA damage mediated by free radicals were detected. Four mutagenic lesions (2,6-diamino-4-hydroxy-5-formamidopyrimidine, 8-hydroxyadenine, 5-hydroxycytosine, and 8-hydroxyguanine) examined by gas chromatography/mass spectrometry and one corresponding 8-hydroxy-2'-deoxyguanosine by a method of HPLC with electrochemical detection increased in cortical DNA two- to fourfold (p < 0.05) during 10-20 min of reperfusion. The damage to gamma-actin and DNA polymerase-beta genes was detected within 20 min of reperfusion based on the presence of formamidopyrimidine DNA N-glycosylase-sensitive sites. These genes became resistant to the glycosylase within 4-6 hr of reperfusion, suggesting a reduction in DNA damage and presence of DNA repair in nuclear genes. These results suggest that nuclear genes could be targets of free radicals.

8OHdG levels in brain do not indicate oxidative DNA damage in Alzheimer's disease

Accumulation of oxidative DNA damage has been proposed to underlie aging and neurodegenerative diseases such as Alzheimer's Disease (AD). The DNA adduct 8-hydroxy-2'-deoxyguanosine (8OHdG) is considered a good indicator of oxidative DNA damage. To investigate whether this type of DNA damage is involved in AD etiology, 8OHdG levels were determined in postmortem human brain tissue of controls and AD patients (in frontal, occipital, and temporal cortex and in hippocampal tissue). Parametric studies in rat revealed no influences of postmortem delay, repeated freezing/thawing or storage time. In human brain, approximately two 8OHdG molecules were present per 10(5) 2'-deoxyguanosines. In AD patients and controls, 8OHdG-levels were not related to age, sex, or brain region. Also, no differences were found between controls and AD patients. It was concluded that 8OHdG in nuclear DNA, although present throughout the brain in fairly high amounts, does not accumulate with age, nor does it appear to be involved in AD. More detailed studies are required to extend this conclusion to other types of oxidative damage.

Single- and double-strand DNA breaks in rat brain cells after acute exposure to radiofrequency electromagnetic radiation

We investigated the effects of acute (2-h) exposure to pulsed (2-micros pulse width, 500 pulses s(-1)) and continuous wave 2450-MHz radiofrequency electromagnetic radiation on DNA strand breaks in brain cells of rat. The spatial averaged power density of the radiation was 2mW/cm2, which produced a whole-body average-specific absorption rate of 1.2W/kg. Single- and double-strand DNA breaks in individual brain cells were measured at 4h post-exposure using a microgel electrophoresis assay. An increase in both types of DNA strand breaks was observed after exposure to either the pulsed or continuous-wave radiation, No significant difference was observed between the effects of the two forms of radiation. We speculate that these effects could result from a direct effect of radiofrequency electromagnetic energy on DNA molecules and/or impairment of DNA-damage repair mechanisms in brain cells. Our data further support the results of earlier in vitro and in vivo studies showing effects of radiofrequency electromagnetic radiation on DNA.

Cell death in Alzheimer's disease evaluated by DNA fragmentation in situ

Loss of nerve cells is a hallmark of the pathology of Alzheimer's disease (AD), yet the patterns of cell death are unknown. By analyzing DNA fragmentation in situ we found evidence for cell death not only of nerve cells but also of oligodendrocytes and microglia in AD brains. In average, 30 times more brain cells showed DNA fragmentation in AD as compared to age-matched controls. Nuclear alterations suggestive of apoptosis were rare in degenerating cells. Even though the majority of degenerating cells were not located within amyloid deposits and did not contain neurofibrillary tangles, neurons situated within areas of amyloid deposits or affected by neurofibrillary degeneration revealed a higher risk of DNA fragmentation and death than cells not exposed to these AD changes.

Chromosomal fragility associated with familial Alzheimer's disease

To test whether chromosomal instability is associated with familial Alzheimer's disease, we examined breakage on X chromosomes of fibroblasts derived from patients with familial Alzheimer's disease, using gene cotransfer methodology. The X chromosome is a convenient target for analyzing DNA breakage because of its numerous markers and ease of selection in rodent-human hybrid cells. Patients with familial Alzheimer's disease, including the large Nova Scotia Alzheimer's kindred, show a significantly lower cotransfer of the X-linked glucose-6-phosphate dehydrogenase (G6PD) gene with the selected HPRT gene in hybrid cells, indicating breakage between the markers. Lower cotransfer of the more distant X-linked gene, MIC-2, was statistically significant in this kindred, but not in other patients with familial Alzheimer's disease. The distance between MIC2 and HPRT is sixfold to ninefold greater than that between HPRT and G6PD, suggesting that there may be a "hot spot" for breakage in the latter interval on the X chromosome of patients with familial Alzheimer's disease. The somatic cell hybrid model provides insights into underlying mechanisms for chromosomal breakage induced by the Alzheimer defect. A hypothesis implicating a candidate gene, C1-THF synthase, in the generation of chromosome instability in the pathogenesis of familial Alzheimer's disease, is presented.

Possible factors in the etiology of Alzheimer's disease

Inherited cases of Alzheimer's disease (AD) comprise only a very small proportion of the total. The remainder are of unknown etiopathogenesis, but they are very probably multifactorial in origin. This article describes studies on four possible factors: aluminum; viruses--in particular, herpes simplex type I virus (HSV1); defective DNA repair; and head trauma. Specific problems associated with aluminum, such as inadvertent contamination and its insolubility, have led to some controversy over its usage. Nonetheless, the effects of aluminum on animals and neuronal cells in culture have been studied intensively. Changes in protein structure and location in the cell are described, including the finding in this laboratory of a change in tau resembling that in AD neurofibrillary tangles, and also the lack of appreciable binding of aluminum to DNA. As for HSV1, there has previously been uncertainty about whether HSV1 DNA is present in human brain. Work in this laboratory using polymerase chain reaction has shown that HSV1 DNA is present in many normal aged brains and AD brains, but is absent in brains from younger people. Studies on DNA damage and repair in AD and normal cells are described, and finally, the possible involvement of head trauma is discussed.

Chromosome studies in Alzheimer's disease patients: distribution of dicentric breakpoints in lymphocytes irradiated in vitro

A previous study showed a significant increase in dicentric frequency in lymphocytes irradiated in vitro from non-familial Alzheimer's disease patients compared to normal age-matched controls. This study examined the distribution of the chromosome breakpoints involved in the dicentric formation and found a non-specific increase in all chromosomes.

Case report: retinitis pigmentosa following cytotoxic chemotherapy in Usher's syndrome

Ocular toxicity is an uncommon complication of cytotoxic chemotherapy. Retinitis pigmentosa complicating cancer chemotherapy has not been reported. A patient with probable Usher's syndrome (congenital sensorineural deafness) had apparent acceleration of retinitis pigmentosa with blindness following cytotoxic chemotherapy for non-Hodgkin's lymphoma. Retinitis pigmentosa, a feature of Usher's syndrome, usually develops as a slowly progressive process. The rapid acceleration of retinopathy following tumor therapy suggests a possible relationship to the cytotoxic chemotherapy. Lymphocytes and fibroblasts from patients with Usher's syndrome are hypersensitive to the x-ray type of DNA-damaging agents. The DNA-damaging effects of chemotherapy may have accelerated the progression of retinitis pigmentosa in this patient.

Gender differences and the interpretation of genetic instability in Alzheimer's disease

The neuronal degeneration and death which characterize Alzheimer's disease (AD) may stem from a constitutive genetic instability related to DNA repair deficits. To test this hypothesis, we treated peripheral blood lymphocytes from persons with AD, age-matched controls, and young controls with two drugs that induce chromosome breakage. Bleomycin, a radiomimetic antineoplastic drug, causes single- and double-stranded DNA breaks through the generation of activated oxygen radicals. Methyl methane-sulfonate (MMS) is a monofunctional alkylating agent that binds covalently to DNA. Cells were grown in culture for 72 h, with drug treatments for 4 h (bleomycin) or 24 h (MMS) prior to harvest. Fifty cells per subject per drug were scored for chromosome breakage. Breakage rates for both drugs in AD women were significantly higher than those in age-matched control women. This was not the case in men, due to the very high induced breakage rates seen in the age-matched normal control men. Because the induced breakage rates in AD women and AD men are equivalent, it seems likely that an independent factor may be contributing to genetic instability in the normal control men. Our findings indicate that the interpretation of the response of AD lymphocyte chromosomes to DNA-damaging chemicals can be strongly confounded by the effects of gender ratio in the control population sampled. These findings have important implications for the design of future studies of Alzheimer's disease, as well as for the assessment of health risks in unaffected elderly populations.

Decreased DNA repair capacity in familial, but not in sporadic Alzheimer's disease

Using the alkaline filter elution technique we determined the induction and disappearance of DNA single-strand breaks (SSB) in freshly isolated peripheral blood lymphocytes (PBL) from 43 Alzheimer's disease (AD) patients and 48 normal, healthy age- and sex-matched control subjects following in vitro exposure to N-ethyl-N-nitrosourea (ENU). The mean percentage SSB disappearance in PBL from control subjects at 1 h after ENU treatment was 41.4 +/- 2.9%; this was not significantly different from that found in samples from AD patients which had no (n = 16) or one (n = 12) first-degree relative with dementia (42.5 +/- 8.2% and 43.0 +/- 4.4%, respectively; p greater than 0.75). However, in PBL of 15 AD patients with at least two first-degree relatives with dementia the mean percentage SSB disappearance was 23.6 +/- 5.8%, which was significantly lower than that found in controls (p less than 0.01) or in the other AD patients (p less than 0.02).

Chromosomal radiosensitivity of lymphocytes from Alzheimer's disease patients

We have examined chromosome aberrations in gamma irradiated (3 Gy) lymphocytes from five patients with Alzheimer's disease (AD). In each case, the number of dicentrics was significantly higher than the number in irradiated lymphocytes from five age matched normal subjects, the mean value for AD cells being about 25% higher. There was no significant difference in number of acentrics between AD and normal cells. Examination of the number of first, second, and third division metaphases, using fluorescence plus Giemsa staining, indicated that there was no difference in cycling time between AD and normal cells, and that after irradiation both groups showed the same mitotic delay. The similarity of our findings to those of others with irradiated Down's syndrome cells (from adult patients) is discussed.

Increased levels of DNA breaks in cerebral cortex of Alzheimer's disease patients

It has been hypothesized that Alzheimer's disease (AD) is caused by an accumulation of damage in DNA due to defective DNA-repair (21). Attempts to test this hypothesis by determining the activity of DNA-repair systems in nonneuronal cells from AD patients and controls so far provided conflicting results. An alternative approach is the direct comparison of DNA-damage levels in neuronal tissue of AD patients and controls. In the present study we assayed the level of DNA breaks and alkali-labile sites in cerebral cortex tissue samples from AD patients and controls obtained from rapid autopsies. Our data on 11 AD patients and 8 control subjects indicate an at least two-fold higher level of DNA damage in cortex of AD patients as compared to controls.

Alzheimer's disease: theories of causation

There are many theories to explain the cause of Alzheimer's disease. None is mutually exclusive of the others, and it may be that all are correct. The only problem may be that we do not understand which is the primary cause and which are the secondary effects of the primary abnormality in the disease. It is almost certain that Alzheimer's disease, as we recognize it today, is heterogeneous. One has only to think of the early-onset and late-onset familial cases to realize that this is so. All of the theories have experimental evidence to support them, and all have generated experiments to substantiate them. Some of them have generated potential concepts for treatment, none of which at present have proved to be successful. When in the end the underlying etiology of the condition is discovered, it will be possible to fit all of the experimental observations into place. It appears at present that the most likely breakthroughs in our understanding will come from detailed sequencing of the paired helical filaments and from breakthroughs in the field of molecular genetics studying the gene for familial Alzheimer's disease.

Decreased DNA repair in familial Alzheimer's disease

Alterations in the capacity of a cell to repair DNA lesions play an important role in a number of human diseases. We and others have demonstrated defective DNA repair of alkylation damage in cells from patients with Alzheimer's disease. It has been hypothesized that this defect is related to the cause of Alzheimer's disease and results in the accumulation of lesions in the central nervous system neurons. One prediction of this hypothesis is that in dominantly inherited Alzheimer's disease, the repair defect will be present in half of the offspring of affected patients long before they develop symptoms of the disease. In order to test the hypothesis that decreased DNA repair is responsible for familial Alzheimer's disease and their at-risk offspring we have studied DNA repair in these individuals after exposure of lymphoblasts to alkylating agents. Our results indicate that cell lines from affected patients repair significantly less damage in 3 h than cell lines from healthy controls. A small number of at-risk individuals were also studied and some of these had lower levels of repair, although more cell lines from individuals in this group must be studied. These findings provide further support for defective DNA repair playing a role in the pathogenesis of Alzheimer's disease.

Familial aggregation of multiple myeloma and central nervous system diseases

Degenerative central nervous system diseases such as Alzheimer's disease and lymphoreticular malignancies such as multiple myeloma occur with increased frequency with advancing age. Relatives of early-onset Alzheimer's disease patients may have an increased risk of lymphoreticular malignancies. This led us to evaluate the family history of central nervous system diseases in a case-control study of multiple myeloma. Thirteen of 439 multiple myeloma cases had one or more first-degree relatives with degenerative or demyelinating central nervous system disease. In comparison, there were nine "positive" family histories in 1,317 matched hospital controls (relative risk = 4.4, 95% confidence interval = 1.9-10.3). Relative risks for the component categories of Parkinson's disease, multiple sclerosis, and miscellaneous degenerative central nervous system diseases were 3.0, 4.0 and 11.9, respectively. Our findings suggest that the degenerative and demyelinating central nervous system diseases and the lymphoreticular malignancies may comprise an etiologically related group of "protean diseases." These diseases may have a shared genetic susceptibility, possibly an immunologic abnormality. The varied disease manifestation in family members suggests a second necessary etiologic step of a variable and possibly environmental nature.

Diminished mitogen-induced calcium uptake by lymphocytes from Alzheimer patients

Recent studies demonstrate diminished calcium uptake by cultured skin fibroblasts from Alzheimer patients. To determine if altered calcium homeostasis is also present in tissue taken from Alzheimer patients, calcium homeostasis was assessed in mitogen-stimulated lymphocytes. Calcium uptake by lymphocytes from Alzheimer patients was 10%-15% lower (p less than 0.002) than that of lymphocytes from age-matched controls. However, neither superficially bound nor total calcium was altered by Alzheimer's disease. These small differences in uptake may reflect larger differences in cytosolic calcium, in later calcium-mediated events, or in the response of particular subsets of lymphocytes. Their biological significance remains to be determined.

Recent views on amyotrophic lateral sclerosis with emphasis on electrophysiological studies

Peripheral electrophysiological studies are of particular value of elucidating the anatomy and pathophysiology of neuromuscular diseases, but they can also help in providing clues to the etiology of the disease. Recent studies of the motor units in chronic denervating conditions including amyotrophic lateral sclerosis (ALS) are reviewed. These indicate that reinnervation is a relatively active process which compensates for the progressive loss of motoneurons in ALS until more than 50% of the motoneurons have died. There seems to be no predilection for death of motoneurons of any particular size in ALS. Fasciculations may arise both proximally and distally. The dying-back change is not a major feature of ALS. These and other data cast doubt on the etiological theories that ALS arises from premature aging of motoneurons, deficiency of motoneuron trophic factors, or an inhibitor of a motoneuronal sprouting factor, and point to the need to study metabolic changes intrinsic to the motoneuron in ALS.

Deficient DNA repair in amyotrophic lateral sclerosis cells

We studied survival and DNA repair capacity in cultured sporadic ALS and control skin fibroblasts after treatment with DNA damaging agents producing different types of lesions. Mean survival in ALS and control fibroblasts was similar after exposure to ultraviolet (UV) light, x-rays and mitomycin C (MMC). Both mean survival and mean unscheduled (repair) DNA synthesis (UDS) were significantly reduced in ALS fibroblasts following treatment with the alkylating agent methyl methane sulfonate (MMS). These data suggest that ALS cells are relatively deficient in the repair of alkylation damage, possibly of apurinic/apyrimidinic sites, and that they are not unduly sensitive to DNA damage produced by UV light, x-rays and MMC. Normal survival and UDS seen in some patients' cells after MMS treatment indicate a spectrum of repair efficiency, and suggest heterogeneity of the biochemical defect in ALS.

Altered metabolic properties of cultured skin fibroblasts in Alzheimer's disease

Alzheimer's disease is associated with selective neuronal loss, the cause of which is undetermined. Evidence indicating a predisposing genetic factor associated with this disease suggests that important alterations may be expressed in tissues other than the brain. Because abnormal glucose and energy-related metabolism have been identified in both in vivo and in vitro studies of brain, we conducted a study to examine related measures in cultured skin fibroblasts from six patients with Alzheimer's disease and seven age-matched controls. After 60 minutes' incubation, the production of 14CO2 from [U-14C]glucose and lactate production were significantly higher in the cells from the group of patients with Alzheimer's disease. The increase of 14CO2 production, but not the production of lactate, was most evident after a more rapid period of metabolic activity in the first 10 minutes of incubation. By contrast, 14CO2 production from [U-14C]glutamine, which is probably the major substrate of oxidative metabolism in these cells, was significantly reduced in the Alzheimer's disease cells following longer (120-minute) incubations. Oxygen uptake by cell suspensions was also significantly reduced in the group with Alzheimer's disease. These results indicate that complex metabolic differences are expressed in nonneural tissues from some patients with Alzheimer's disease and may provide important clues to the pathogenesis of this disorder.

Alzheimer's disease cells exhibit defective repair of alkylating agent-induced DNA damage

The most common cause of senile and presenile dementia is Alzheimer's disease, a disorder with an undetermined cause. A number of studies have indicated that neurons from patients with Alzheimer's disease have decreased ribonucleic acid levels and reduced protein synthesis. Recent studies using lymphoblasts from patients with Alzheimer's disease have indicated that these cells are more sensitive to deoxyribonucleic acid (DNA)-alkylating agents. We have used cell survival, unscheduled DNA synthesis, and alkaline elution to assess the capacity for DNA repair in skin fibroblasts from normal control subjects, control subjects with central nervous system disease, and patients with Alzheimer's disease. Our results indicate that the Alzheimer's disease cells, unlike normal cells, fail to repair methylmethane sulfonate-induced DNA damage. Both normal and Alzheimer's disease cells are able to ameliorate the effects of ultraviolet light. These results indicate that a specific pathway for DNA repair is affected in Alzheimer's disease. The repair defect may be related to the cause of the disease or may be the cause of the disease.

Antemortem markers of Alzheimer's disease

This review examines various approaches to the development of antemortem markers of Alzheimer's disease. Among the procedures discussed are: neurochemical and histopathologic studies of the cholinergic system, concentrating on CSF and blood plasma; genetic studies; imaging and electrophysiological studies; and neuroendocrine studies.

Quantitative protein profiling: determining lexotypes

The lexotype of a cell is defined as a set of quantitative characters of its informational macromolecular gene products, notably proteins, as observed under specified environmental conditions. This definition can be applied to cells in several ways that need to be distinguished. It can refer to the protein lexotype, to RNA lexotypes; to the steady-state lexotype, synthesis lexotype, functional protein lexotype; to the in situ lexotype and standard-environment lexotype. When used without qualification, the term lexotype may be applied to the standard-environment, steady-state protein lexotype. Some difficulties that currently limit our ability to determine lexotypes are assessed. Reasons are given why abnormal cellular states, such as states of disease, should often be characterizable by means of protein markers not themselves involved in the disease process and why one expects to find markers in tissues other than the one in which a certain pathological process may be anticipated to occur. There are three routes through which biological systems can produce secondary protein markers, namely through gene regulatory chains, through chromosomal gene linkage, and through "physiological linkage" of genes. The partly stable, partly shifting, yet defined relations between tissue lexotypes are considered. A number of potentially important fields of application of rigorous quantitative analyses of protein profiles are listed. One particular use of the technology is to investigate a hypothesis linking aging to degenerative diseases with late onset. According to this hypothesis, such diseases appear in later life as the cellular concentration of the active form of a protein passes a certain threshold in the course of the aging process.

Alzheimer's disease. A metabolic systems degeneration?

Alzheimer's disease can be considered a late-onset system degeneration, characteristically involving certain populations of cholinergic neurons but eventually involving other cells as well. Decreases in cerebral metabolic rate occur in it and may reflect not only decreased neuronal activity, but also deficiencies in metabolic enzymes. Abnormalities reported in nonneural Alzheimer tissues suggest that at the molecular level it is a systemic disease whose biochemical aspects can usefully be studied in nonneural tissues. Alzheimer's disease can be formulated as one of a number of metabolic encephalopathies that impair central cholinergic function.

Parkinson's disease and Alzheimer's disease: hypersensitivity to X rays in cultured cell lines

Fibroblast and/or lymphoblastoid lines from patients with several inherited primary neuronal degenerations are hypersensitive to DNA-damaging agents. Therefore, lymphoblastoid lines were irradiated from patients with sporadic Parkinson's disease (PD), Alzheimer's disease, and amyotrophic lateral sclerosis. The mean survival values of the eight Parkinson's disease and of the six Alzheimer's disease lines, but not of the five amyotrophic lateral sclerosis lines, were less than that of the 28 normal lines. Our results with Parkinson's disease and Alzheimer's disease cells can be explained by a genetic defect arising as a somatic mutation during embryogenesis, causing defective repair of the X-ray type of DNA damage. Such a DNA repair defect could cause an abnormal accumulation of spontaneously occurring DNA damage in Parkinson's disease and Alzheimer's disease neurons in vivo, resulting in their premature death.

Deficient repair of DNA lesions in Alzheimer's disease fibroblasts

DNA strand breaks, resulting from treatment with N-methyl-N'-nitro-N-nitrosoguanidine, were repaired more slowly in four strains of familial Alzheimer's disease fibroblasts than in five strains of fibroblasts from age-matched normals. These results were not due to differences between the two cell types in in vitro ages, in the initial DNA damage or in drug-induced cell lysis. Bleomycin-induced DNA double-strand breaks were repaired equally efficiently by both types of cells. Alzheimer's disease cells may have a DNA repair defect, which may be involved in the pathogenesis of this disease.

Red blood cell abnormalities in Alzheimer disease

In a prospective, double-blind study of 84 unselected persons in a dementia clinic, the red blood cell/plasma choline ratios were found to be significantly higher in 47 subjects with clinically defined Alzheimer disease (DAT) than in 37 non-DAT, nondepressed subjects (3.54 +/- 0.48 versus 2.04 +/- 0.34, p less than 0.02). The latter group included intellectually intact subjects as well as patients with other dementias who were comparable to the Alzheimer patients in age, sex, and degree of cognitive impairment. The elevated mean ratio reflected the greater proportion of Alzheimer patients with high red blood cell plasma choline ratios. These elevated ratios appeared to be related to both increases in red cell content and decreases in plasma choline. The authors conclude that the results confirm and extend those previously reported in short series of patients and agree with other evidence that Alzheimer disease has systemic manifestations in nonneural cells, which may be useful in further investigations of the disease's cellular pathophysiology.

Hypersensitivity to ionizing radiation in cultured cells from Down syndrome patients

Down syndrome is caused by trisomy of chromosome 21 and is comprised of a constellation of abnormalities including neuropathological features that closely resemble those characterizing the neurodegeneration of Alzheimer disease. Because cultured cell lines from patients with Alzheimer disease and other neurodegenerations have a hypersensitivity to the lethal effects of DNA-damaging agents, we studied the response of Down syndrome lymphoblastoid lines to the lethal effects of ionizing and ultraviolet radiation. Lines from the four Down syndrome patients were more sensitive to X-rays than lines from 28 normal donors (P = 10(-4)), while survival of the Down syndrome lines after ultraviolet irradiation was not significantly different from normal. This hypersensitivity to X-rays, which may reflect defective repair of X-ray-induced DNA damage, represents the first abnormality common to cultured cells from both Down syndrome and Alzheimer disease patients.

Elevated red blood cell/plasma choline ratio in dementia of the Alzheimer type: clinical and polysomnographic correlates

In a prospective study we have observed a shift in distribution of red blood cell (RBC)/plasma choline ratios among patients with probable dementia of the Alzheimer type (DAT), compared with healthy controls and depressed patients. Fifteen of 22 DAT patients (68%) showed RBC/plasma choline ratios greater than 1.9, in contrast to 9 of 26 healthy controls (35%) and 7 of 20 depressives (35%). These significant differences confirm and expand earlier observations. The subgroup of DAT patients with elevated RBC/plasma choline ratios is older and more cognitively impaired, shows later onset of dementia, and has less rapid eye movement (REM) sleep than the DAT subgroup with normal RBC/plasma choline ratios. Within the entire group of DAT patients, moreover, the RBC/plasma choline ratio shows a significant inverse correlation with REM sleep latency. These findings are discussed in relation to abnormalities in other nonneural Alzheimer tissues and within the context of cholinergic involvement in both DAT and the timing of REM sleep.

Hypersensitivity to DNA-damaging agents in cultured cells from patients with Usher's syndrome and Duchenne muscular dystrophy

Lymphoblastoid lines from nine Usher's syndrome (recessively inherited retinitis pigmentosa and congenital sensorineural deafness) patients (representing eight kindreds) and from ten Duchenne muscular dystrophy patients (representing seven kindreds) showed a small but statistically significant hypersensitivity to the lethal effects of X-rays, as measured by the cellular ability to exclude the vital dye trypan blue, when compared with lines from 26 normal control subjects. Fibroblast lines from the Usher's syndrome patients, treated with X-rays or the radiomimetic, DNA-damaging chemical N-methyl-N'-nitro-N-nitrosoguanidine, also showed a statistically significant hypersensitivity when compared to normal fibroblast lines. These findings are consistent with the possibility that defective DNA repair mechanisms may be involved in the pathogenesis of these degenerative diseases.

Studies of cellular radiosensitivity in hereditary disorders of nervous system and muscle

Skin fibroblasts from patients with familial dysautonomia, Duchenne muscular dystrophy and Charcot-Marie-Tooth disease show normal sensitivity to ionising radiation, as measured by post-irradiation clonal growth. Previous reports of cellular hypersensitivity to ionising radiation and other DNA-damaging agents in familial dysautonomia and Duchenne muscular dystrophy have not been confirmed.