Cerebrospinal fluid pH and monoamine and glucolytic metabolites in Alzheimer's disease

CSF in Alzheimer's disease

Alzheimer's disease (AD) is a progressive brain amyloidosis that injures brain regions involved in memory consolidation and other cognitive functions. Neuropathologically, the disease is characterized by accumulation of a 42-amino acid protein called amyloid beta, and N-terminally truncated fragments thereof, in extracellular senile plaques together with intraneuronal inclusions of hyperphosphorylated tau protein in neurofibrillary tangles, and neuronal and axonal degeneration and loss. Clinical chemistry tests for these pathologies have been developed for use on cerebrospinal fluid samples. Here, we review what these markers have taught us on the disease process in AD and how they can be implemented in routine clinical chemistry. We also provide an update on new marker development and ongoing analytical standardization effort.

Sustained choroid plexus function in human elderly and Alzheimer's disease patients

We and other investigators have postulated deterioration of essential choroid plexus (CP) functions in some elderly and especially Alzheimer’s disease patients based on apparent anatomical, histological and pathological changes in CP. We have termed this putative phenomenon CP failure. By focusing on four essential energy-requiring CP functions, specifically ascorbic acid (AA) and folate transport from blood into CSF, transthyretin synthesis and secretion into CSF, and electrolyte/acid–base balance in CSF, we were able to evaluate the hypothesis of CP failure by reviewing definitive human data. In both healthy elderly and Alzheimer’s disease patients, the CP functions normally to transport AA and folates actively from blood into CSF, synthesize and secrete transthyretin into CSF, and maintain CSF acid–base balance and ion concentrations. These human CSF compositional data provide no support for the notion of CP failure in elderly humans and Alzheimer’s disease patients.

Transmitter deficits in Alzheimer's disease

The pattern of neurotransmitter pathway losses in Alzheimer's disease are reviewed. Deficits of the cholinergic pathway from the nucleus basalis, the noradrenergic pathway from the locus coeruleus and the serotoninergic pathway from the raphe nuclei are established. Cortical somatostatin interneurons are affected and dopaminergic neurons may be affected although these may be late or secondary phenomena in the disease process. Other neuronal systems, particularly in the hippocampus and temporal cortex, are also damaged. However, the disease is not one of generalised neuronal atrophy since some neurons are selectively spared. The established pathway-specific losses are discussed in relation to the clinical symptomatology and the pathology of the disorder. The biochemical and histological findings are compared with similar measurements made on tissues from other dementing disorders in an attempt to trace features common to dementias. Finally, as an addendum, a hypothesis is briefly outlined which attempts to explain the common features of the affected neurons and the pathogenesis of the disorder.

Effects of acidosis on the distribution of processing of the beta-amyloid precursor protein in cultured hippocampal neurons

Reported increases in brain lactate production in Alzheimer disease led us to test the hypothesis that lactic acid acidosis alters the processing of the beta-amyloid precursor protein, beta PP, in neurons. To test this proposition, embryonic rat hippocampal neurons were first cultures for 4 d in serum-free B27/neurobasal medium. Lactic acid at 0.5 and 1 mg/mL (pH 7.1 and, 6.9, respectively) caused a dose-dependent increase in cellular beta-amyloid immunoreactivity detected with antibody 4G8. Acidosis did not affect secretion of beta PP or its derivatives into the medium. The cytoplasmic production of beta PP was slightly reduced by acidosis without a differential effect on maturation or proteolytic processing. In the substrate-bound material, which was insoluble in nonionic detergent, acidosis caused increases in an N-terminal 75-kDa band, a C-terminal 72-kDa band, and potentially amyloidogenic bands at 35 and 38 kDa. Processing to the 4-kDa amyloid beta protein was not observed in these early pure rat neuronal cultures. These results suggest that mild acidosis id sufficient to alter neuronal processing to the amyloid precursor protein into potentially amyloidogenic forms and increase certain beta PP fragments bound to the substrate. If a similar process occurs in the presence of other cell types in the aging brain, acidosis may stimulate an extracellular deposition of amyloid and contribute to the pathogenesis of Alzheimer disease.

CSF monoamine metabolites in old age dementias

Cerebrospinal Fluid (CSF) levels of the main metabolites of monoamines (MHPG, 5-HIAA, and HVA) were measured in patients with early onset (AD) and late-onset (SDAT) Alzheimer's disease, vascular dementia (VD), and elderly controls. Psychobehavioral assessment was carried out by means of MMSE and GBS. Mean MHPG levels did not differ from controls; 5-HIAA was lower in VD when compared to both controls and SDAT. HVA was decreased in AD, SDAT, and VD with respect to controls. Significant correlations between HVA and psycho-behavioral parameters were observed in SDAT and VD groups, whereas no relationship was documented in AD. The SDAT group was divided in SDAT-A (age at onset: greater than 65 less than or equal to 80 yr) and SDAT-B (age at onset: greater than 80 yr). SDAT-A had significantly lower CSF HVA values than SDAT-B (165 +/- 64 vs 235.7 +/- 85). SDAT-B HVA levels were similar to those observed in controls. Correlation analysis between HVA and neuropsychological variables was significant in SDAT-A, but not in SDAT-B. These results might support the evidence of SDAT heterogeneity.

Enantiomeric composition of urinary salsolinol in parkinsonian patients after Madopar

Urinary salsolinol output had been shown to be lower in Parkinsonian patients than in controls and to increase largely after L-dopa therapy. It had also been established that the R enantiomer of salsolinol is either the predominant or the sole enantiomer present in the urine of healthy subjects. When Madopar was administered to Parkinsonians, the enantiomeric composition of urinary salsolinol showed an S/R ratio around 1. Considering brain and plasma concentrations in dopamine, acetaldehyde and pyruvate, it is suggested that, under physiological conditions, urinary salsolinol should have a central origin in humans. Conversely, urinary salsolinol in Madopar-treated Parkinsonian patients might be predominantly formed at the periphery.

Tacrine, a drug with therapeutic potential for dementia: post-mortem biochemical evidence

A review of biochemical findings is presented which support the idea that Alzheimer's disease represents a condition for which tetrahydroaminoacridine (tacrine) may have a beneficial effect. There is evidence that clinical and histopathologic hallmarks of the disease relate to cholinergic and serotonergic dysfunction, with less obvious abnormalities in other neurotransmitters (aspartate, dopamine, gamma-aminobutyrate, glutamate, noradrenaline and somatostatin). Clinically relevant concentrations of tacrine may ameliorate the above presynaptic deficits without producing harmful (neurotoxic) effects of aspartate and glutamate. The disease seems to be associated with an early and clinically relevant degeneration of some neurons with cortical perikarya that release these amino acid transmitters. Studies are now required on the effect of tacrine on postulated harmful peptide-bond hydrolase activity within and around such cells.

Dopaminergic system and monoamine oxidase-B activity in Alzheimer's disease

The possible involvement of dopaminergic neurons in dementia of Alzheimer type (AD/SDAT) was studied in autopsied brains from 20 patients with AD/SDAT. Dopamine (DA) concentrations were decreased significantly in the temporal cortex, hippocampal cortex and hippocampus in AD/SDAT patients. Levels of homovanillic acid (HVA) were not altered compared to controls. The HVA/DA ratio was significantly higher in the hippocampus of AD/SDAT patients, suggesting overactivity of the remaining DA neurons. Histological findings of substantia nigra suggesting coexistent pathology of Parkinson's disease (PD) found in 25% of cases were associated with lowered levels of DA in striatum and with reduced HVA in CSF. The activity of monoamine oxidase-B was significantly increased in the cortical areas and in the hippocampus, obviously reflecting the underlying cell loss and substantial gliosis in these areas of the brain. In general, DA neurons seemed to be only mildly involved in AD/SDAT. Coexistent PD pathology can explain the loss of DA in the striatum and the presence of clinical PD symptoms in some patients with AD/SDAT. Otherwise the clinical relevance of these dopaminergic alterations is unclear.

Neuropsychological test performance and CSF levels of monoamine metabolites in healthy volunteers and patients with Alzheimer's dementia

Fifteen patients (51-78 yrs) with mild to moderately severe Alzheimer's dementia and 18 healthy subjects of the same age were examined by clinical rating scales and a battery of neuropsychological tests. Levels of the monoamine metabolites homovanillic acid (HVA), 3-methoxy-4-hydroxyphenyl glycol (MHPG) and 5-hydroxyindoleacetic acid (5-HIAA) were determined in the lumbar cerebrospinal fluid (CSF). Correlations between clinical, psychological and biochemical measures were calculated in order to elucidate whether monoaminergic mechanisms are of importance for the maintenance of cognitive abilities in normal and pathological aging. The patients' performance was severely impaired in all neuropsychological tests. The mean levels of monoamine metabolites, however, did not differ between patients and volunteers. The correlations between psychological test scores and CSF metabolite levels were generally low, but mostly negative, associating a poor performance to a high activity of brain monoaminergic neurons. Thus, among the volunteers high 5-HIAA and MHPG levels correlated with poor performance in the Picture completion and the Trail making tests--measures of visuo-perceptual and visuo-motor skills. In the demented patients poor performance in the memory tests was associated with high levels of HVA and 5-HIAA. The results indicate that monoamine neuron activity is not a primary determinant for cognitive abilities in healthy elderly subjects or in demented patients. The slight negative correlation between cognitive function and metabolite concentrations in the patients may reflect a disturbance in a dopaminergic-cholinergic balance due to degenerative changes of central cholinergic pathways.

Dose-dependent effects of deprenyl on CSF monoamine metabolites in patients with Alzheimer's disease

Deprenyl, a monoamine oxidase (MAO) inhibitor with selective effects on MAO type-B at low doses, was administered to 13 patients with dementia of the Alzheimer type (DAT), a disorder reported to be associated with increased brain MAO-B activity. Cerebrospinal fluid was obtained for measurement of three monoamine metabolites, homovanillic acid (HVA), 5-hydroxyindoleacetic acid (5-HIAA), and 3-methoxy-4-hydroxyphenylglycol (MHPG), by high pressure liquid chromatography with electrochemical detection. Deprenyl treatment (10 mg/day) for 3-4 weeks was associated with small but statistically significant reductions in HVA (21%) and 5-HIAA (15%) compared to baseline values. Subsequent administration of deprenyl at the higher dose of 40 mg/day for 3-4 more weeks led to greater reductions in HVA (40%) and MHPG (43%) than 5-HIAA (20%). These dose-dependent reductions are consistent with in vitro biochemical and anatomical data from primate brain suggesting that at low doses of deprenyl, MAO-B inhibition might be expected to selectively affect dopamine and serotonin-containing neurons, while at higher doses (which lead to MAO-A as well as MAO-B inhibition), noradrenergic neurons may become relatively more affected by the drug.

Monoamine metabolite concentrations in lumbar cerebrospinal fluid of patients with histologically verified Alzheimer's dementia

Concentrations of 3-methoxy-4-hydroxyphenylglycol (MHPG), 5-hydroxy indoleacetic acid (5-HIAA) and homovanillic acid (HVA) were determined in lumbar cerebrospinal fluid (CSF) from control subjects and patients of both presenile and senile age with histologically verified Alzheimer's dementia. CSF HVA increased with age in control but not in Alzheimer patients. HVA and 5-HIAA in the CSF of presenile Alzheimer patients was lower than that of age matched control subjects.

Dexamethasone suppression test and serum prolactin in dementia disorders

The dexamethasone suppression test (DST) was performed on 21 patients with dementia of the Alzheimer type (DAT), 11 patients with multi-infarct dementia (MI) and 14 healthy controls. Twelve of the DAT patients and eight of the MI patients showed abnormal lack of suppression, compared with just one member of the control group. Abnormal DST was related to dementia as such and not to age or depression, or to levels of CSF monoamine metabolites. Basal serum prolactin concentrations were not increased.

Effect of nafronyl on lactate and pyruvate in the cerebrospinal fluid of patients with senile dementia

In a single-blind study, 12 men (mean age 63 years) with senile dementia were given nafronyl in a dosage of 100 mg eight times daily for a week, followed by 100 mg four times daily for 12 weeks. Rigorous clinical, laboratory and psychometric assessments revealed no toxicity and no significant effects on vital functions. In the cerebrospinal fluid, the ratio of lactate to pyruvate decreased--a finding consistent with an increase in the aerobic metabolism of glucose.

Homovanillic acid and 5-hydroxyindoleacetic acid levels in cerebrospinal fluid of patients with senile dementia of Alzheimer type

The possibility of disturbed dopamine and serotonin metabolism in senile dementia of Alzheimer type was studied. The basal concentrations of homovanillic acid (HVA) and 5-hydroxyindoleacetic acid (5-HIAA) in cerebrospinal fluid (CSF) were studied in 28 patients with senile dementia of Alzheimer type and in 13 controls of similar age with no neurological disease. The concentrations of HVA were significantly reduced in the dementia patients compared to the concentrations of the controls. The values of HVA were also significantly reduced in the most severely demented patients compared to the less severely demented ones. There was a slight but statistically significant decrease in the 5-HIAA levels in the dementia patients compared to the levels of the controls. The 5-HIAA levels were reduced in the most severely demented patients compared to the controls but not when compared with the less severely demented patients. It is concluded that in severe forms of senile dementia of Alzheimer type, there is a decrease in the levels of HVA and 5-HIAA in CSF which may reflect a decreased turnover of dopamine and serotonin. Patients diagnosed as senile dementia of Alzheimer type, but with less severe symptoms, had levels of HVA and 5-HIAA similar to controls.

Changes in the monoamine containing neurones of the human CNS in senile dementia

In thirteen cases of senile dementia of the Alzheimer type severe loss of nerve cells from the locus caeruleus was frequently seen together with reductions in nucleolar volume and cytoplasmic RNA in surviving cells, averaging 14 and 21 per cent respectively. These histological findings were matched in two cases by biochemical measurements of loss of noradrenaline from all brain regions examined, ranging from 10 per cent in temporal cortex to 53 per cent in hypothalamus. By contrast, neither nucleolar volume nor cytoplasmic RNA was altered in cells of the substantia nigra, nor was dopamine content significantly altered in most regions. In vascular dementia neither noradrenaline nor dopamine metabolism was changed except in regions of local circulatory deficiency. These findings provide evidence of a primary degeneration of the noradrenergic system in Alzheimer type dementia.

Cytophotometric mapping of neuronal changes in senile dementia

Results of a cytophotometric study have shown a widespread reduction in cytoplasmic RNA of nerve cells. It appears, therefore, that although certain aspects of the symptomatology of senile dementia may be accounted for by lesions in particular anatomical sites, the main part of the neurological disturbance is related to more broadly based changes in nerve cell metabolism affecting much, if not all, of the CNS.

Effect of cerebrospinal fluid removal on cerebral blood flow and metabolism in patients with Alzheimer's disease versus recent stroke

Cerebral hemispheric blood flow (HBF) and metabolism were measured before and after withdrawal of 20 to 30 ml of cerebrospinal fluid (CSF) over a 10-minute interval in eight patients with recent cerebral infarction and in four patients with Alzheimer's disease (AD). Immediately after CSF removal HBF decreased significantly in the AD group (-14%) but showed no significant change in the stroke group (-5%). There was rapid reduction in cerebral venous O2 content and some increase in cerebral venous PCO2 appearing within 60 seconds of CSF withdrawal, interpreted as a rapid reduction of cerebral blood flow (CBF) as judged by cerebral A-VO2 differences. The reduction in CBF was confirmed by the hydrogen clearance method. Reduction of CBF in response to lowering CSF pressure is presumably of neurogenic origin since it was rapid and occurred without changes in PaCO2 or MABP. Furthermore, measurement of HBF demonstrated that cerebral metabolism constant after CSF removal. It is postulated that in AD, reduction of HBF following CSF withdrawal is mediated by a disordered neurogenic veno-arterial vasoconstriction reflex which is stimulated by rapid reduction in CSF pressure (CSFP). In patients with stroke, when cerebral perfusion pressure is increased by lowering CSFP, CBF is maintained constant most likely by a physiological cerebral veno-arterial vasoconstrictive reflex. Apparently, this vasocontrictive reflex becomes excessive in Alzheimer's disease, possibly due to cerebral neurogenic imbalance.

Distribution of cerebral degeneration in Alzheimer's disease. A clinico-pathological study

Seven cases of Alzheimer's disease were studied in detail from a clinical and neuropathological point of view. The degenerative process was mapped with regard to regional variations in the intensity, extent and consistency of focal accentuations. The degeneration was regularly found to be most pronounced in certain areas: maximal cortical degeneration occurred in the medial temporal (limbic) area and, in the lateral hemisphere, consistently within a field expanding from the posterior inferior temporal areas to the adjoining portions of the parieto occipital lobes. In addition, the posterior cingulate gyrus was severely involved. On the other hand certain areas were notably and consistently spared or less involved, mainly the anterior cingulate gyrus and the calcarine and central sensory motor areas (primary projection areas). The frontal lobes occupied an intermediate position, being less severely involved than is usually reported. The clinical symptoms correlated well with this pattern of degeneration. Thus groups of symptoms such as memory dysfunction, emotional and personality alterations, and some symptoms of the Klüver-Bucy syndrome, were referable to the limbic lesions. The cortical lesions of the temporo-parieto-occipital association cortex correlated with the symptoms of agnosia, aphasia and apraxia, which were recorded in all cases. The relative sparing of the primary projection areas correspond well to findings of retained motility and perception even in later stages of the disease. The relative sparing of the frontal lobes and the anterior cingulate gyrus was related to the preservation of habitual personality traits. The pattern described may be related to ontogenetic features, and the tendency to focalization to the age of disease onset. The role of genetic factors and of other diseases is discussed.

Probenecid: dosage, levels in plasma and cerebrospinal fluid (CSF) and influence upon CSF levels of homovanillic acid (HVA) and 5-hydroxyindoleacetic acid (5-HIAA) in the rabbit

Probenecid retards the efflux of acid monoamine metabolites from the brain tissue and CSF to the blood. The probenecid-induced accumulation of these metabolites is held to be indicative of the turnover rate of the corresponding amines. Although the penetration of probenecid into the CSF does not proceed at a constant rate, Korf et al. (1972) and Sjöstrom (1972) have shown a correlation between CSF levels of probenecid and that of HVA and 5-HIAA. In this study an attempt was made to establish the relationship between doses of probenecid and levels of this compound in plasma and CSF; between levels in plasma and CSF; and between CSF levels of probenecid and of HVA and 5-HIAA. This study was performed in a homogeneous group of laboratory rabbits. All correlations proved to be significant. The implications of these results for studies using the probenecid technique are discussed.