Sulfated glycosaminoglycans: a common constituent of all amyloids?

In the present investigation, we analyzed whether sulfated glycosaminoglycans are a common constituent in many different types of amyloid. Serial sections of amyloidotic tissue were stained for the presence of: (a) amyloid by using Congo Red, and (b) glycosaminoglycans by using both the sodium sulfate Alcian blue method and Alcian blue, pH 5.7, with varying concentrations of magnesium chloride. Our results show that sulfated glycosaminoglycans are always associated anatomically with amyloid deposits regardless of the nature of the protein deposited. Sulfated glycosaminoglycans were found in tissues containing AA, AL, inherited cutaneous amyloid, and senile cardiac amyloid (prealbumin). Additionally, we provide evidence that sulfated glycosaminoglycans are closely associated with the amyloid of medullary carcinoma of the thyroid (prothyrocalcitonin), and neuritic plaques, neurofibrillary tangles, and congophilic angiopathy in Alzheimer's disease. It is postulated that these sulfated glycosaminoglycans can influence the folding of diverse proteins such that all forms of amyloid show a significant beta-pleated sheet component.     

Characterization of high affinity binding between laminin and Alzheimer's disease amyloid precursor proteins.

BACKGROUND: In vivo amyloid formation apparently involves several extracellular matrix components that are usually found associated with basement membranes. These include laminin, heparan sulfate proteoglycan, collagen type IV, and entactin. These components have also been found in neuritic plaques. We have therefore been examining interactions between extracellular matrix components and the Alzheimer's amyloid precursors (AAPs). EXPERIMENTAL DESIGN: Binding interactions of laminin with AAP-695, -751, and -770 were examined using a solid phase enzyme-linked immunosorbent assay technique. RESULTS: Objective, quantitative analyses of the laminin AAP-695, -751, and -770 binding data reveal two binding sites for laminin, with Kd values of 1 x 10(-10) M and 1 x 10(-8) M. Zinc and dithiothreitol profoundly stimulate laminin binding to AAPs. Furthermore, zinc fingers were found in the laminin amino acid sequences. Previous binding studies of AAPs with the basement membrane heparan sulfate proteoglycan revealed similar affinities. A particular order of addition of laminin and heparan sulfate proteoglycan to AAPs can be demonstrated. CONCLUSIONS: These avid interactions with extracellular matrix proteins likely reflect normal functions of the AAPs and may be involved in nucleation events in Alzheimer-type amyloid formation.     

In vivo fragmentation of heparan sulfate by heparanase overexpression renders mice resistant to amyloid protein A amyloidosis

Amyloid diseases encompass >20 medical disorders that include amyloid protein A (AA) amyloidosis, Alzheimer's disease, and type 2 diabetes. A common feature of these conditions is the selective organ deposition of disease-specific fibrillar proteins, along with the sulfated glycosaminoglycan, heparan sulfate. We have generated transgenic mice that overexpress human heparanase and have tested their susceptibility to amyloid induction. Drastic shortening of heparan sulfate chains was observed in heparanase-overproducing organs, such as liver and kidney. These sites selectively escaped amyloid deposition on experimental induction of inflammation-associated AA amyloidosis, as verified by lack of material staining with Congo Red, as well as lack of associated polysaccharide, whereas the same tissues from control animals were heavily infiltrated with amyloid. By contrast, the spleens of transgenic mice that failed to significantly overexpress heparanase contained heparan sulfate chains similar in size to those of control spleen and remained susceptible to amyloid deposition. Our findings provide direct in vivo evidence that heparan sulfate is essential for the development of amyloid disease.     

AA protein in experimental murine AA amyloid fibrils: a high resolution ultrastructural and immunohistochemical study comparing aldehyde-fixed and cryofixed tissues.

In a previous study, the fibrils of experimental murine AA amyloid were found to be microfibril-like structures with the AA protein (in the form of 1 nm wide flexible filaments) on their exterior surface. In this study, we have re-examined the AA amyloid fibrils with advanced methods of cryofixation and freeze substitution which are known to retain ultrastructural detail as close as possible to the living state. The observations were compared to those obtained with conventional methods of aldehyde fixation. Cryofixation and freeze substitution confirmed the microfibril-like nature of the inner part of the AA amyloid fibril. The AA protein was present on the exterior surface in the form of 3 nm wide 'helical rods' formed by the tight coiling of the 1 nm wide AA protein flaments. The 'helical rods' were arranged parallel to the axis of the fibril and to one another with a uniform center-to-center distance of 5 nm. This arrangement was fully preserved in amyloid fibrils after cryofixation and freeze substitution, but was present in only some areas of formaldehyde fixed mouse spleen AA amyloid This conformation and orientation of AA protein is likely to be that in its native state, given the ability of these advanced methods of biological preservation to retain structures close to that of the living state. This information shoulld be of considerable value in comparing the structure of amyloid fibrils observed in situ with those isolated from tissue or generated in vitro.     

Maturation of human fetal responses to airborne sound in low- and high-risk fetuses

The purpose of the study was to characterize the onset and maturation of airborne sound-elicited responses in low- and high-risk preterm fetuses. In Study 1, a total of 91 low-risk fetuses at 27, 30, 33, and 36 weeks GA received three sound trials at 90, 100, 105 and 110 dB and three no-stimulus control trials. The onset of cardiac acceleration and body movement responses occurred at 30 weeks GA. Maturation of the cardiac response was observed with a decrease in threshold from 105-110 dB at 33 weeks GA to 100-105 dB at 36 weeks GA. In Study 2, the procedure was similar except that the 43 high-risk fetuses at 27, 30 and 33 weeks GA did not receive sounds at 90 dB. For the high-risk fetuses, the onset of cardiac and motor responses also occurred at 30 weeks GA. At 33 weeks GA, those high-risk fetuses subsequently born at term showed an increased magnitude of the cardiac acceleration response compared to low-risk fetuses. The results indicate that both low- and high-risk fetuses begin responding to sounds at the same gestational age. Differential responses observed over gestation in the high-risk group most likely indicate differential functional development of the auditory-response system.     

Temporal relationship between glycosaminoglycan accumulation and amyloid deposition during experimental amyloidosis. A histochemical study

The temporal relationship between glycosaminoglycan (GAG) accumulation and amyloid deposition was determined in two models of amyloid induction. In the first model amyloid was induced rapidly using amyloid-enhancing factor and AgNO3 as an inflammatory stimulus. In the second model amyloid was induced by daily injections of azocasein. Congo red staining was used to demonstrate amyloid, and both the sulfated Alcian blue and Alcian blue (pH 5.7)-MgCl2 methods were used to demonstrate GAGs. In the rapid model, amyloid was first detected in the splenic perifollicular areas 36 hours after induction. The initial presence of GAGs was also seen at 36 hours and in the exact locale where the amyloid was found. Amyloid was first seen in the liver about the central veins at 48 hours. GAGs in the liver appeared coincidentally with and in the same location as the amyloid. In the traditional model (azocasein injections) amyloid did not appear in the spleen until day 6 to 7, again with coincidental GAG deposition. The present study shows that amyloid-associated GAGs appear in the tissues together with the AA protein and are not a function of the tissue type. The appearance of the GAGs is also not a function of the nature of the inflammatory agent or its length of action but appears to be part of the process involved in the deposition of the AA protein.     

Comparison of fetal behavior in low- and high-risk pregnancies

Meta-analyses were conducted on archival data of human fetal behavior to identify differential behavior among high-risk fetuses in pregnancies complicated by threatened preterm delivery, maternal hypertension or diabetes compared with low-risk fetuses in uneventful pregnancies, delivering as healthy, full-term infants. Data for a total of 493 fetuses (260 high risk, 233 low risk) from 23 weeks' gestation to term who participated in a study using a standardized protocol including observations of spontaneous and auditory-induced behavior were retrieved from our laboratory database. There were no differences in spontaneous behaviors when scored using clinical criteria for the nonstress test and biophysical profile; however, there were differences in the magnitude of the behaviors measured in the tests. Developmental differences were observed between those threatening to deliver early and the fetuses of hypertensive and diabetic mothers. The latter two groups differed little from one another but differed from low-risk fetuses in their response to auditory stimulation. We concluded that differences in behavior among high-risk groups suggest that atypical fetal behaviors may represent adaptation to condition specific insult rather than a generalized response to insult per se. The finding that high-risk fetuses showed atypical responses to auditory stimuli indicates a need to examine the relation between fetal auditory function and later language acquisition.     

Anaemia and red blood cell transfusion in intracranial neurosurgery: a comprehensive review

Both anaemia and blood transfusion are associated with poor outcomes in the neurosurgical population. Based on the available literature, the optimal haemoglobin concentration for neurologically injured patients appears to be in the range of 9.0–10.0 g dl^?1, although the individual risks and benefits should be weighed. Several perioperative blood conservation strategies have been used successfully in neurosurgery, including correction of anaemia and coagulopathy, use of antifibrinolytics, and intraoperative cell salvage. Avoidance of non-steroidal anti-inflammatory drugs and starch-containing solutions is recommended given the potential for platelet dysfunction.     

Maternal heart rate variability and fetal behavior in hypertensive and normotensive pregnancies

The relation between maternal heart rate variability (HRV) and fetal behavior was examined in hypertensive and normotensive pregnant women. A total of 40 mother-fetal pairs (n = 20 normotensive mothers; n = 20 hypertensive mothers) at 33-41 weeks' gestation were observed using a standardized procedure lasting approximately 50 min. It included the following measurements: maternal beat-by-beat arterial blood pressure and HRV; spontaneous fetal heart rate (HR), body and breathing movements; and an estimate of amniotic fluid volume. The women in the hypertensive group had higher average body mass index (BMI) (33.7 vs. 28.8 kg/m2) than the normotensive group. In the normotensive group, there was no association between maternal HRV and fetal gestational age, HR, body or breathing movements. In the hypertensive group, maternal HRV measures of low-frequency, high-frequency, and total power were associated with fetal gestational age; also, there was an association between maternal autonomic modulation of HR and fetal spontaneous HR. These findings suggest that the maternal autonomic system influences fetal cardiac function in pregnancies complicated by hypertension.     

Binding of vascular heparan sulfate proteoglycan to Alzheimer's amyloid precursor protein is mediated in part by the N-terminal region of A4 peptide

The exact mechanisms of deposition and accumulation of amyloid in senile plaques and in blood vessels in Alzheimer's disease remain unknown. Heparan sulfate proteoglycans may play an important role in amyloid deposition in Alzheimer's disease. Previous investigations have demonstrated high affinity binding between heparan sulfate proteoglycans and the amyloid precursor, as well as with the A4 peptide. In the current studies, a specific vascular heparan sulfate proteoglycan found in senile plaques bound with high affinity to two amyloid protein precursors (APP₆₉₅ and APP₇₇₀). Vascular heparan sulfate proteoglycan also bound the Alzheimer's amyloid A4 peptide, and not other amyloid protein precursor regions studied, with high affinity. Both heparan sulfate glycosaminoglycan chains and chemically deglycosylated vascular heparan sulfate proteoglycan protein core bound to A4. High affinity interactions between vascular heparan sulfate proteoglycan and the A4 peptide may play a role in the process of amyloidogenesis in Alzheimer's disease, by localizing the site of deposition of A4, protecting A4 from further proteolysis, or by promoting aggregation and fibril formation.