beta-Amyloid-(1-42) is a major component of cerebrovascular amyloid deposits: implications for the pathology of Alzheimer disease

Reinvestigation of the chemical structure of beta-amyloid peptide (A beta) deposits in the vascular tissue of Alzheimer disease brains revealed that the 42-residue form A beta-(1-42), rather than the more soluble A beta-(1-40) form, is the predominant peptide. Following removal of the surrounding tissue with SDS and collagenase, A beta was solubilized in formic acid and purified by Superose 12 chromatography. Peptides generated by enzymatic and chemical digestion of the A beta were purified by HPLC and characterized by amino acid analysis, sequence analysis, and mass spectrometry. In the leptomeningeal vessels, the average ratio of A beta-(1-42)/A beta-(1-40) was 58:42, whereas in the parenchymal vessels this ratio was 75:25. Interestingly, vascular A beta contains considerably less isomerized and racemized aspartyl residues than does neuritic plaque A beta, suggesting that the vascular amyloid is "younger." The discrete nature of the bands and spherical deposits of A beta associated with arterioles and capillaries, respectively, suggests that this amyloid arises from the vascular tissue itself. Increasing A beta deposition appears to lead to the distortion and occlusion of capillaries, which may contribute significantly to the pathology of Alzheimer disease.

Morphological and biochemical analyses of amyloid plaque core proteins purified from Alzheimer disease brain tissue

Amyloid plaque cores were purified from Alzheimer disease brain tissue. Plaque core proteins were solubilized in formic acid which upon dialysis against guanidinium hydrochloride (GuHCl) partitioned into soluble (approximately 15%) and insoluble (approximately 85%) components. The GuHCl-soluble fraction contained beta-amyloid1-40, whereas the GuHCl-insoluble fraction was fractionated into six components by size exclusion HPLC: S1 (> 200 kDa), S2 (200 kDa), S3 (45 kDa), S4 (15 kDa), S5 (10 kDa), and S6 (5 kDa). Removal of the GuHCl reconstituted 10-nm filaments composed of two intertwined 5-nm strands. Fractions S5 and S6 also yielded filamentous structures when treated similarly, whereas fractions S1-S4 yielded amorphous aggregates. Chemical analysis identified S4-S6 as multimeric and monomeric beta-amyloid. Immunochemical analyses revealed alpha 1-antichymotrypsin and non-beta-amyloid segments of the beta-amyloid precursor protein within fractions S1 and S2. Several saccharide components were identified within plaque core protein preparations by fluorescence and electron microscopy, as seen with fluorescein isothiocyanate- and colloidal gold-conjugated lectins. We have shown previously that this plaque core protein complex is more toxic to neuronal cultures than beta-amyloid. The non-beta-amyloid components likely mediate this additional toxicity, imposing a significant influence on the pathophysiology of Alzheimer disease.

Reduced cerebral cortical but elevated striatal concentration of somatostatin-like immunoreactivity in dominantly inherited olivopontocerebellar atrophy

Somatostatin-like immunoreactivity (SLI) was measured in the brains of nine patients with dominantly inherited olivopontocerebellar atrophy (OPCA), who all had a marked deficit of the cholinergic marker choline-acetyltransferase (ChAT) in the cerebral cortex and striatum. Mean concentrations of SLI in OPCA were significantly reduced by 42-58% in parietal and occipital cortices and frontal cortical eye fields, but were normal in other cortical areas, including two subdivisions of the temporal cortex which show marked depletions of both SLI and ChAT in Alzheimer's disease. This dissociation of SLI and ChAT indicates that a cortical cholinergic deficit does not invariably lead to reduction of somatostatin. In the caudate nucleus, the region of OPCA brain having the most severe ChAT deficit (-81%), SLI levels were significantly elevated by 46% and were negatively and significantly correlated with ChAT activities (r = -0.66). The SLI alterations could be due to abnormal somatostatin metabolism or release, or an increased number of somatostatin-containing neurons and could contribute to the brain dysfunction of OPCA.

Chromosome 14 and late-onset familial Alzheimer disease (FAD)

Familial Alzheimer disease (FAD) is genetically heterogeneous. Two loci responsible for early-onset FAD have been identified: the amyloid precursor protein gene on chromosome 21 and the as-yet-unidentified locus on chromosome 14. The genetics of late-onset FAD is unresolved. Maximum-likelihood, affected-pedigree-member (APM), and sib-pair analyses were used, in 49 families with a mean age at onset > or = 60 years, to determine whether the chromosome 14 locus is responsible for late-onset FAD. The markers used were D14S53, D14S43, and D14S52. The LOD score method was used to test for linkage of late-onset FAD to the chromosome 14 markers, under three different models: age-dependent penetrance, an affected-only analysis, and age-dependent penetrance with allowance for possible age-dependent sporadic cases. No evidence for linkage was obtained under any of these conditions for the late-onset kindreds, and strong evidence against linkage (LOD score < or = -2.0) to this region was obtained. Heterogeneity tests of the LOD score results for the combined group of families (early onset, Volga Germans, and late onset) favored the hypothesis of linkage to chromosome 14 with genetic heterogeneity. The positive results are primarily from early-onset families. APM analysis gave significant evidence for linkage of D14S43 and D14S52 to FAD in early-onset kindreds (P < .02). No evidence for linkage was found for the entire late-onset family group. Significant evidence for linkage to D14S52, however, was found for a subgroup of families of intermediate age at onset (mean age at onset > or = 60 years and < 70 years). These results indicate that the chromosome 14 locus is not responsible for Alzheimer disease in most late-onset FAD kindreds but could play a role in a subset of these kindreds.

Reductions in parietal and temporal cerebral metabolic rates for glucose are not specific for Alzheimer's disease

Reduction in the regional cerebral metabolic rate for glucose (rCMRglc) in the parietal and temporal regions has been shown in Alzheimer's disease (AD). The specificity of these findings for this disease state is uncertain. We repeatedly measured rCMRglc with positron emission tomography and [18F]2-fluoro-2-deoxy-D-glucose in the resting state in a 68 year old man with slowly progressive dementia who, during life, was initially diagnosed as having dementia of the Alzheimer type, then Parkinson disease with dementia, but was found to have only Parkinson's disease at necropsy. Metabolic ratios (rCMRglc/mean grey CMRglc) were significantly (p < 0.05) reduced in parietal and temporal regions, as well as in the prefrontal and premotor areas. This pattern was similar in regional distribution and magnitude of the defect to that seen in patients with probable AD. These results suggest that reductions of glucose metabolism in association neocortex in AD are not specific to the disease process, but may be related to the dementia state.

Elevated stimulatory and reduced inhibitory G protein alpha subunits in cerebellar cortex of patients with dominantly inherited olivopontocerebellar atrophy

Although guanine nucleotide binding proteins (G proteins) are one of the critical components of signal transduction units for various membrane receptor-mediated responses, little information is available regarding their status in brain of patients with neurodegenerative illnesses. We measured the immunoreactivity of G protein subunits (Gs alpha, Gi alpha, Go alpha, Gq/11 alpha, and G beta) in autopsied cerebellar and cerebral cortices of 10 end-stage patients with dominantly inherited olivopontocerebellar atrophy (OPCA) who all had severe loss of Purkinje cell neurons and climbing fiber afferents in cerebellar cortex. Compared with the controls, the long-form Gs alpha (52-kDa species) immunoreactivity was significantly elevated by 52% (p < 0.01) in the cerebellar cortex of the OPCA patients, whereas the Gi1 alpha concentration was reduced by 35% (p < 0.02). No statistically significant differences were observed for Go alpha, Gi2 alpha, G beta 1, G beta 2, or Gq/11 alpha in cerebellar cortex or for any G protein subunit in the two examined cerebral cortical subdivisions (frontal and occipital). The cerebellar Gs alpha elevation could represent a compensatory response (e.g., sprouting, reactive synaptogenesis) by the remaining cerebellar neurons (granule cells?) to neuronal damage but also might contribute to the degenerative process, as suggested by the ability of Gs alpha, in some experimental preparations, to promote calcium flux. Further studies will be required to determine the actual functional consequences of the G protein changes in OPCA and whether the elevated Gs alpha is specific to OPCA cerebellum, because of its unique cellular pattern of morphological damage, or is found in brain of patients with other progressive neurodegenerative disorders.

Obesity and body fat distribution in New Zealanders: a pattern of coronary heart disease risk

AIMS

To describe the prevalence of obesity and the body fat distribution of New Zealanders. To discuss this in the context of the coronary heart disease risk.

METHODS

Body weight and height, body mass index (BMI), waist:hip ratio (WHR) and six skinfold measurements were determined for 3204 randomly selected New Zealanders who responded to an invitation to a health check (response rate 56%).

RESULTS

In the study sample BMI generally increased with age. Fifty five percent of men and 38 per cent of women aged 18-64 had a BMI exceeding 25, and of these 13 per cent and 10 per cent were obese (BMI > 30). WHR was greater in men than in women of all ages, and a third of the men and a quarter of the women had values exceeding 0.9 and 0.8 respectively. Central skinfold measurements (subscapular, suprailiac and abdominal) were lowest in young men, but rose markedly with age and were similar to women above age 35. Limb skinfolds were lower in men.

CONCLUSIONS

This survey indicates that a large percentage of New Zealanders are overweight or obese and their excess body fat tends to be centrally distributed, especially in men. Obesity is thus a significant health problem in New Zealand.

Effect of isoenergetic intake of three or nine meals on plasma lipoproteins and glucose metabolism

To investigate the effects of meal frequency on plasma lipid and carbohydrate metabolism, 19 healthy normocholesterolemic free-living men and women consumed their usual diet as three or nine meals per day in random order for 2 wk each. There was no significant difference in macronutrient intake. Compared with the three-meal/d diet, nine meals per day reduced fasting plasma total, low-density lipoprotein (LDL), and high-density lipoprotein (HDL) cholesterol by 6.5% (P < 0.005), 8.1% (P < 0.005), and 4.1% (P < 0.05), respectively. Body weight, fasting triglycerides, apolipoproteins A-I and B, and the LDL-HDL cholesterol ratios were not different for the two diets, as were 24-h urinary C peptide-creatinine ratios and insulin-glucose response to a glucose load. The insulin-glucose curve measured over 3 h in the evening after the evening meal was flatter for the nine meals, but the areas under the curves were not significantly different. Increasing meal frequency while maintaining a constant nutrient intake produces a small but significant decrease in LDL cholesterol in normolipidemic free-living subjects.

Structural alterations in the peptide backbone of beta-amyloid core protein may account for its deposition and stability in Alzheimer's disease

The structure of beta-amyloid (beta A) from Alzheimer disease brains was examined to determine if post-translational modifications might be linked to the abnormal deposition of this peptide in the diseased tissue. The beta A peptides were isolated from the compact amyloid cores of neuritic plaques and separated from minor glycoprotein components by size-exclusion high-pressure liquid chromatography (HPLC). This parenchymal beta A has a maximal length of 42 residues, but shorter forms with "ragged" NH2 termini are also present. Tryptic peptide analysis revealed heterogeneity in the beta A1-5 and beta A6-16 peptides, each of which eluted as four peaks on reverse phase HPLC. Amino acid composition and sequence analyses, mass spectrometry, enzymatic methylation, and stereoisomer determinations revealed that these multiple peptide forms resulted from structural rearrangements of the aspartyl residues at beta A positions 1 and 7. The L-isoaspartyl form predominates at each of these positions, whereas the D-isoaspartyl, L-aspartyl, and D-aspartyl forms are present in lesser amounts. beta A purified from the leptomeningeal microvasculature contains the same structural alterations as parenchymal beta A, but is 2 residues shorter at its COOH terminus. Using two different purification protocols, and using a synthetic beta A1-42 peptide as a control, we show that these modifications arose endogenously and were not caused by the experimental manipulations. The abundance of structurally altered aspartyl residues may profoundly affect the conformation of the beta A protein within plaque cores and thus significantly impact normal catabolic processes designed to limit its deposition. These alterations may therefore contribute to the production and stability of beta-amyloid deposits in Alzheimer brain tissue.

Fatty acid composition and the oxidation of low-density lipoproteins

The effect of the fatty acid composition of low-density lipoprotein (LDL) on copper-ion-catalyzed oxidation of isolated LDL was examined in 18 normolipidemic men. The decrease in LDL linoleic acid concentration (delta L) during oxidation was found to be strongly correlated with initial LDL linoleic acid concentration (r = 0.976, n = 18, P < 0.001), whereas the production of thiobarbituric acid reacting substances (TBARS) was not. The concentration of oleic acid in LDL was then increased significantly (mean increase 20%, P < 0.05) in 8 male volunteers by a daily dietary supplement of rapeseed oil/muesli for 4 weeks. The mean delay before copper-ion-catalyzed production of conjugated dienes (the lag phase) was significantly (P < 0.001) greater in LDL isolated after the study period (67 min) than that of before the study period (40 min). The rate of formation of conjugated dienes, delta L and TBARS production during oxidation of LDL was not significantly altered by the rapeseed oil/muesli supplement. These results suggest that the linoleic acid content of LDL is a determinant of individual variability in LDL oxidation, and that a rapeseed oil/muesli dietary supplement reduces the susceptibility of LDL to oxidation.

Parenteral nutrition in the critically ill: use of a medium chain triglyceride emulsion

OBJECTIVES

The study investigated the use of an intravenous lipid emulsion containing medium chain triglycerides (MCTs) in critically ill patients, and compared the effects with those of a conventional long chain triglyceride (LCT) preparation.

DESIGN

Patients received a parenteral nutrition regime including either 500 ml 20% Lipofundin MCT/LCT (1/1) per day, or 500 ml 20% Lipofundin S (LCT) infused over 8 h each evening.

SETTING

The patients were receiving treatment, including assisted ventilation, in the Intensive Care Unit of a large teaching hospital. All patients on this unit for at least 3 days and who were likely to receive parenteral nutrition for at least a week were considered, unless they had severe renal or liver disease, or trauma/major surgery in the previous 3 days. Because ICU patients are a heterogenous group, subjects were randomised within clinical groups to receive either lipid. There were 24 patients entered into the study and the data on 20 matched patients is reported.

MEASUREMENTS AND RESULTS

Blood specimens were collected pre-TPN, daily at 0800 and after 5 h lipid infusion on days 1 and 6. Urine collections (24 h) were also performed. There were no apparent adverse effects due to the new MCT/LCT emulsion. Plasma ketone and glycerol concentrations were higher during MCT/LCT infusion, but 8 h post infusion plasma levels of ketones, triglycerides, non-esterified fatty acids and glucose were similar. Urinary carnitine excretion was high in all patients and was not significantly different between the groups. Nitrogen balance was less negative in patients receiving MCT/LCT on days 6 and 9.

CONCLUSION

MCTs are rapidly hydrolysed and oxidised to fatty acids and ketones which can be readily utilised. This study indicates that intravenous lipid emulsion containing MCT are safe in critically ill patients and may have advantages over LCT. The number and range of patients studied was, however, small and larger studies are needed.

Interlaboratory histopathologic assessment of Alzheimer neuropathology: different methodologies yield comparable diagnostic results

Three investigators have applied different histopathologic methods (modified Bielschowsky silver methods, Congo red-gallocyanin) to differentiate Alzheimer's disease (AD) (n = 7 subjects; four with very mild dementia and three with moderate to advanced dementia) neuropathology from brain changes associated with aging in three nondemented individuals who had been evaluated using a validated dementia severity staging instrument [Washington University Clinical Dementia Rating (CDR)] generally within a year of death. The presence of elevated numbers of neocortical (frontal and temporal) diffuse, mature, and total senile plaques (SP) was strongly correlated with the presence of clinical AD but did not equate with CDR dementia severity. Neocortical neurofibrillary tangle (NFT) density as well as hippocampal NFT and SP density in this small series did not differentiate statistically between AD and controls. NFT density appeared to correlate with CDR better than SP density. Quantitative histopathologic assessment of AD markers in only a few brain regions can accurately predict the presence of clinical AD, including the very mild form of the disease. This is especially true for SP in the neocortex.

Glycine absorption from irrigation fluid during endoscopic resection of rectal tumours

A significant rise in plasma glycine concentration was observed in nine elderly patients undergoing endoscopic transanal resection of rectal tumours using glycine solution for irrigation. Despite the obvious absorption of glycine, plasma sodium concentration and osmolality were not significantly altered, except in a patient whose rectal wall was perforated. In this case plasma sodium and osmolality fell, and the patient developed hyperammonaemia. Potentially adverse metabolic consequences may occur when there are surgical complications, but in the absence of such problems the absorption of glycine appears to cause little effect.

Normal serotonin but elevated 5-hydroxyindoleacetic acid concentration in cerebellar cortex of patients with dominantly-inherited olivopontocerebellar atrophy

Beas-Zarate and coworkers (Eur. J. Pharmacol., 198 (1991) 7-14) recently reported markedly reduced concentration of presynaptic serotonin neurotransmitter markers in cerebellum of rodents which had suffered destruction of the inferior olivary-cerebellar (climbing fibre) projections by the neurotoxin 3-acetylpyridine; these experimental animal data suggested that serotonin might be one of the neurotransmitters released by climbing fibres. We measured the concentration of serotonin and its major metabolite 5-hydroxyindoleacetic acid (5-HIAA) in autopsied cerebellar cortex of 14 patients with dominantly-inherited olivopontocerebellar atrophy (OPCA) who all had near-total degeneration of the inferior olivary climbing fibres. As compared with the controls, mean concentration of serotonin in cerebellar cortex of the OPCA patients was normal whereas 5-HIAA levels (+79%, P less than 0.02) and 'turnover' ratio 5-HIAA/serotonin (+148%, P less than 0.05), on average, were significantly elevated. These data do not support the notion that serotonin is a predominant neurotransmitter of the human climbing fibre. However, the markedly elevated serotonin turnover ratio suggests the possibility of increased serotonergic neuronal activity, which might alter, and perhaps improve, the functioning of the preserved cerebellar cortical neurones in OPCA.

Striatal monoamine neurotransmitters and metabolites in dominantly inherited olivopontocerebellar atrophy

We measured the levels of the monoamine neurotransmitters and metabolites in striatum of 14 patients with end-stage dominantly inherited olivopontocerebellar atrophy (OPCA). On average, dopamine levels were reduced in putamen (-53%), caudate (-35%), and nucleus accumbens (-31%). However, individual patient values showed a wide variation, indicating that mild to moderate striatal dopamine loss is a common but not constant feature of OPCA. Seven patients had marked putamen dopamine loss (-62% to -81%) but without evidence of correspondingly severe substantia nigra cell damage; this suggests the possibility of a "dying-back" phenomenon in which nerve terminal loss precedes cell body degeneration. Severe substantia nigra cell loss with almost total (-95% to -99%) putamen and caudate dopamine depletion was present in two patients; however, none of the 14 patients had had a clinical diagnosis of parkinsonism or was receiving antiparkinsonian medication. Mean striatal serotonin levels were normal, whereas concentrations of the serotonin metabolite 5-hydroxyindoleacetic acid were elevated by 47% to 63%; this suggests increased activity of raphe dorsalis serotonin neurons innervating the striatum, which might aggravate the functional consequences of the dopamine deficit.

Do beans and oat bran add to the effectiveness of a low-fat diet?

The effects of consuming an increased amount of soluble fibre as oat bran or beans were examined in 40 free-living hypercholesterolaemic men and women. The subjects were initially established on a low-fat background diet (29% of energy from fat) and then 55 g low-fibre oat bran, 55 g high-fibre oat bran or 80 g mixed cooked beans were added to their diet in random order for 6 week periods. Body weight and overall composition of the diet did not change. Plasma cholesterol and low-density lipoprotein cholesterol (LDL-C) were unchanged. High-density lipoprotein cholesterol (HDL-C) was significantly higher on all three intervention diets than on the lower fibre run-in diet. Supplementation of a moderately low-fat diet with palatable quantities of oat bran or beans without changing the overall fat intake does not appear to significantly lower cholesterol but may have a benefit by increasing HDL-C and reducing the ratio of LDL-C to HDL-C.

Parenteral nutrition using MCT/LCT or LCT: Effect on the fatty acid composition of plasma triglycerides and platelet phospholipids

Plasma triglyceride fatty acids and platelet phospholipid fatty acids were compared in 20 malnourished patients before and after 8-10 days of total parenteral nutrition which included either a conventional lipid emulsion (LCT) or a new emulsion containing medium chain triglyercides (MCT/LCT). The use of both lipid emulsions altered the fatty acid profiles. The percentage of linoleic acid in the plasma triglycerides increased with both lipid emulsions, but more markedly with LCT. The median percentage after LCT was 25.9 (range 16.9-31.5) which was significantly higher (p < 0.01) than after MCT/LCT - 14.8 (range 6.1-20.2), or in healthy volunteers. After 8-10 days on MCT/LCT the fatty acid profile retained some features of the malnourished state, despite correction of the linoleic acid content. The percentage of linolenic and arachidonic acid in the platelet phospholipids tended to be lower than after LCT use, and the percentage of linoleic acid was significantly less (p < 0.01), the median (range) being 8.2 (4.5-23.8) after MCT/LCT and 11.7 (4.8-16.0) on LCT. Short term use of MCT/LCT emulsion may correct the fatty acid changes of malnutrition rather more slowly and results in a different fatty acid profile to that seen after LCT use. Whether this has any clinical effects is unclear.

Beneficial effect of simvastatin in patients with drug resistant familial hypercholesterolaemia

AIMS

To investigate the effects of simvastatin in patients with heterozygous familial hypercholesterolaemia refractory or intolerant to routine drug therapy.

METHOD

Eighteen patients were given increasing doses of 10, 20 and 40 mg simvastatin for eight week periods, followed by a control period on their former drug therapy in a prospective, crossover clinical study.

RESULTS

Mean total and low density lipoprotein cholesterol (SEM) were significantly lower on 40 mg simvastatin alone than at the end of the control period (7.3 (0.3) mmol/L vs 10.7 (0.4) and 5.1 (0.3) vs 7.8 (0.5) respectively; p less than 0.01). Apo-B was also significantly lower on 40 mg simvastatin (p less than 0.01).

CONCLUSION

Simvastatin offers effective cholesterol lowering for patients with drug resistant familial hypercholesterolaemia.

Preparing medical informaticians: a cross-disciplinary approach

Information systems are a necessity in tomorrow's healthcare environment--but who will be trained to use them and use them well? A whole generation of practitioners is backing away from the challenge--how are they to become educated?

The CIO's key role in healthcare strategic planning

Chief information officers are not longer technicians overseeing the computer room. They're full-fledged members of the healthcare team. What that means, however, is that the CIO must be both willing and able to participate in planning and building the infrastructure that will underpin healthcare delivery in the future.

Is a clinical sociolinguistics possible?

This paper considers the idea of developing a clinical sociolinguistics. Various areas of the field are examined, and the importance of the 'core' area of the correlation of non-linguistic variables with linguistic variables stressed. Issues concerning language and class, region, sex, age and context of utterance are investigated, together with the implications for clinical linguistics. Finally, the difficulty of integrating such issues into clinical assessment is explored, and a tentative step forward suggested along the lines of a 'clinical sociolinguistic checklist'.

Status and progress of hospital information systems (HIS)

Expectations for hospital information systems (HIS) have yet to be realized. Requirements have been defined by the International Medical Informatics Association, health care futurists, and others. With a volatile marketplace and evolving technologies, computerization has been a non-trivial task. However, recent advances in architecture and communication standards promise to make networking possible. In addition, the development of professional workstations and of computer-based patient records linked to new tools and applications can transform health care. For HIS to realize these expectations, however, technology assessment and outcome analysis must play critical roles.