Serum and cerebrospinal fluid neurofilament light chain and glial fibrillary acid protein levels in early and advanced stages of cerebral amyloid Angiopathy

BACKGROUND

Neurofilament light chain (NFL) is a biomarker for neuroaxonal damage and glial fibrillary acidic protein (GFAP) for reactive astrocytosis. Both processes occur in cerebral amyloid angiopathy (CAA), but studies investigating the potential of NFL and GFAP as markers for CAA are lacking. We aimed to investigate NFL and GFAP as biomarkers for neuroaxonal damage and astrocytosis in CAA.

METHODS

For this cross-sectional study serum and cerebrospinal fluid (CSF) samples were collected between 2010 and 2020 from controls, (pre)symptomatic Dutch-type hereditary (D-CAA) mutation-carriers and participants with sporadic CAA (sCAA) from two prospective CAA studies at two University hospitals in the Netherlands. NFL and GFAP levels were measured with Simoa-assays. The association between NFL and GFAP levels and age, cognitive performance (MoCA), CAA-related MRI markers (CAA-CSVD-burden) and Aβ40 and Aβ42 levels in CSF were assessed with linear regression adjusted for confounders. The control group was divided in age < 55 and ≥55 years to match the specific groups.

RESULTS

We included 187 participants: 28 presymptomatic D-CAA mutation-carriers (mean age 40 years), 29 symptomatic D-CAA participants (mean age 58 years), 59 sCAA participants (mean age 72 years), 33 controls < 55 years (mean age 42 years) and 38 controls ≥ 55 years (mean age 65 years). In presymptomatic D-CAA, only GFAP in CSF (7.7*103pg/mL vs. 4.4*103pg/mL in controls; P<.001) was increased compared to controls. In symptomatic D-CAA, both serum (NFL:26.2pg/mL vs. 12.5pg/mL; P=0.008, GFAP:130.8pg/mL vs. 123.4pg/mL; P=0.027) and CSF (NFL:16.8*102pg/mL vs. 7.8*102pg/mL; P=0.01 and GFAP:11.4*103pg/mL vs. 7.5*103pg/mL; P<.001) levels were higher than in controls and serum levels (NFL:26.2pg/mL vs. 6.7pg/mL; P=0.05 and GFAP:130.8pg/mL vs. 66.0pg/mL; P=0.004) were higher than in pre-symptomatic D-CAA. In sCAA, only NFL levels were increased compared to controls in both serum (25.6pg/mL vs. 12.5pg/mL; P=0.005) and CSF (20.0*102pg/mL vs 7.8*102pg/mL; P=0.008). All levels correlated with age. Serum NFL correlated with MoCA (P=0.008) and CAA-CSVD score (P<.001). NFL and GFAP in CSF correlated with Aβ42 levels (P=0.01/0.02).

CONCLUSIONS

GFAP level in CSF is an early biomarker for CAA and is increased years before symptom onset. NFL and GFAP levels in serum and CSF are biomarkers for advanced CAA.

Serum YKL-40 as a Predictive Biomarker of Cerebral Amyloid Angiopathy-Related Intracerebral Hemorrhage Recurrence

Background

Neuroinflammation is a major cause of secondary brain injury in intracerebral hemorrhage (ICH). To date, the prognostic value of YKL-40 (chitinase-3-like-1 protein), a biomarker of neuroinflammation, in cerebral amyloid angiopathy-related intracerebral hemorrhage (CAA-ICH) remains undiscovered.

Objective

To evaluate the relationships between serum YKL-40 and CAA-ICH recurrence.

Methods

Clinical and imaging information of 68 first-onset probable CAA-ICH cases and 95 controls were collected at baseline. Serum YKL-40 was measured by Luminex assay. Cox proportional hazards model was used to analyze the associations between YKL-40 level and CAA-ICH recurrence.

Results

Serum YKL-40 level was significantly higher in CAA-ICH cases than healthy controls (median [interquartile range, IQR], 46.1 [19.8, 93.4] versus 24.4 [13.9, 59.0] ng/mL, p = 0.004). Higher level of YKL-40 predicted increased risk of CAA-ICH recurrence adjusted for age, ICH volume and enlarged perivascular space score (ePVS) (above versus below 115.5 ng/ml, adjusted hazard ratios 4.721, 95% confidence intervals 1.829-12.189, p = 0.001) within a median follow-up period of 2.4 years. Adding YKL-40 to a model of only MRI imaging markers including ICH volume and ePVS score improved the discriminatory power (concordance index from 0.707 to 0.772, p = 0.001) and the reclassification power (net reclassification improvement 28.4%; integrated discrimination index 11.0%).

Conclusions

Serum YKL-40 level might be a candidate prognostic biomarker for CAA-ICH recurrence.

Understanding the Pathophysiology of Cerebral Amyloid Angiopathy

Cerebral amyloid angiopathy (CAA), one of the main types of cerebral small vessel disease, is a major cause of spontaneous intracerebral haemorrhage and an important contributor to cognitive decline in elderly patients. Despite the number of experimental in vitro studies and animal models, the pathophysiology of CAA is still largely unknown. Although several pathogenic mechanisms including an unbalance between production and clearance of amyloid beta (Aβ) protein as well as ‘the prion hypothesis’ have been invoked as possible disease triggers, they do not explain completely the disease pathogenesis. This incomplete disease knowledge limits the implementation of treatments able to prevent or halt the clinical progression. The continuous increase of CAA patients makes imperative the development of suitable experimental in vitro or animal models to identify disease biomarkers and new pharmacological treatments that could be administered in the early disease stages to prevent irreversible changes and disease progression.

Validation of Plasma Proteomic Biomarkers Relating to Brain Amyloid Burden in the EMIF-Alzheimer's Disease Multimodal Biomarker Discovery Cohort

We have previously investigated, discovered, and replicated plasma protein biomarkers for use to triage potential trials participants for PET or cerebrospinal fluid measures of Alzheimer's disease (AD) pathology. This study sought to undertake validation of these candidate plasma biomarkers in a large, multi-center sample collection. Targeted plasma analyses of 34 proteins with prior evidence for prediction of in vivo pathology were conducted in up to 1,000 samples from cognitively healthy elderly individuals, people with mild cognitive impairment, and in patients with AD-type dementia, selected from the EMIF-AD catalogue. Proteins were measured using Luminex xMAP, ELISA, and Meso Scale Discovery assays. Seven proteins replicated in their ability to predict in vivo amyloid pathology. These proteins form a biomarker panel that, along with age, could significantly discriminate between individuals with high and low amyloid pathology with an area under the curve of 0.74. The performance of this biomarker panel remained consistent when tested in apolipoprotein E ɛ4 non-carrier individuals only. This blood-based panel is biologically relevant, measurable using practical immunocapture arrays, and could significantly reduce the cost incurred to clinical trials through screen failure.

Anticoagulants for Treatment of Alzheimer's Disease

Alzheimer's disease (AD) is a multifactorial syndrome with a plethora of progressive, degenerative changes in the brain parenchyma, but also in the cerebrovascular and hemostatic system. A therapeutic approach for AD is reviewed, which is focused on the role of amyloid-β protein (Aβ) and fibrin in triggering intra-brain vascular dysfunction and connected, cognitive decline. It is proposed that direct oral anticoagulants (DOACs) counteract Aβ-induced pathological alterations in cerebral blood vessels early in AD, a condition, known as cerebral amyloid angiopathy (CAA). By inhibiting thrombin for fibrin formation, anticoagulants can prevent accumulations of proinflammatory thrombin and fibrin, and deposition of degradation-resistant, Aβ-containing fibrin clots. These fibrin-Aβ clots are found in brain parenchyma between neuron cells, and in and around cerebral blood vessels in areas of CAA, leading to decreased cerebral blood flow. Consequently, anticoagulant treatment could reduce hypoperfusion and restricted supply of brain tissue with oxygen and nutrients. Concomitantly, hypoperfusion-enhanced neurodegenerative processes, such as progressive Aβ accumulation via synthesis and reduced perivascular clearance, neuroinflammation, and synapse and neuron cell loss, could be mitigated. Given full cerebral perfusion and reduced Aβ- and fibrin-accumulating and inflammatory milieu, anticoagulants could be able to decrease vascular-driven progression in neurodegenerative and cognitive changes, present in AD, when treated early, therapeutically, or prophylactically.

Neprilysin Inhibits Coagulation through Proteolytic Inactivation of Fibrinogen

Neprilysin (NEP) is an endogenous protease that degrades a wide range of peptides including amyloid beta (Aβ), the main pathological component of Alzheimer's disease (AD). We have engineered NEP as a potential therapeutic for AD but found in pre-clinical safety testing that this variant increased prothrombin time (PT) and activated partial thromboplastin time (APTT). The objective of the current study was to investigate the effect of wild type NEP and the engineered variant on coagulation and define the mechanism by which this effect is mediated. PT and APTT were measured in cynomolgus monkeys and rats dosed with a human serum albumin fusion with an engineered variant of NEP (HSA-NEPv) as well as in control plasma spiked with wild type or variant enzyme. The coagulation factor targeted by NEP was determined using in vitro prothrombinase, calibrated automated thrombogram (CAT) and fibrin formation assays as well as N-terminal sequencing of fibrinogen treated with the enzyme. We demonstrate that HSA-NEP wild type and HSA-NEPv unexpectedly impaired coagulation, increasing PT and APTT in plasma samples and abolishing fibrin formation from fibrinogen. This effect was mediated through cleavage of the N-termini of the Aα- and Bβ-chains of fibrinogen thereby significantly impairing initiation of fibrin formation by thrombin. Fibrinogen has therefore been identified for the first time as a substrate for NEP wild type suggesting that the enzyme may have a role in regulating fibrin formation. Reductions in NEP levels observed in AD and cerebral amyloid angiopathy may contribute to neurovascular degeneration observed in these conditions.

ApoA1, ApoJ and ApoE Plasma Levels and Genotype Frequencies in Cerebral Amyloid Angiopathy

The involvement of apolipoproteins, such as the ApoE4 isoform, in Alzheimer's disease (AD) and cerebral amyloid angiopathy (CAA) highlights the fact that certain lipid carriers may participate in soluble β-amyloid (Aβ) transport. Our general aim was to characterize the soluble levels of the apolipoproteins apoE, apoA1 and apoJ/clusterin and their genotype status in patients with CAA. We analyzed the genotypes frequency of APOA1 (rs5069, rs670), CLU (rs11136000, rs1532278, rs7012010, rs9331888) and APOE (rs429358, rs7412) in a cohort of patients with CAA-associated intracerebral hemorrhage (ICH) (n = 59) and compared the results with those from hypertension-associated ICH (n = 42), AD patients (n = 73) and controls (n = 88). In a subgroup of patients, we also determined the plasma concentrations of apoE, apoA1 and apoJ/clusterin. We found increased plasma apoJ/clusterin levels in CAA patients compared to AD patients or controls after adjusting for sex and age (CAA vs. controls, p = 0.033; CAA vs. AD, p = 0.013). ApoA1 levels were not altered between groups, although a strong correlation was observed between plasma Aβ(1-40) and apoA1 among CAA patients (r = 0.583, p = 0.007). Regarding plasma apoE concentration, a robust association between circulating levels and genotype status was confirmed (p < 0.001). Whereas the APOE4 frequency was higher in AD (p < 0.001) and CAA (p = 0.013), the APOA1 and CLU genotypes were not different among groups. In the CAA cohort, the risk-linked CLU variant (C) rs11136000 was associated with white matter hyperintensities (p = 0.045) and the presence of lobar microbleeds (p = 0.023) on MRI. In summary, our findings suggest that apoA1 may act as a physiological transporter of Aβ(1-40) and that apoJ/clusterin appears to be a chaperone related to distinctive lesions in CAA brains.

Blood platelets in the progression of Alzheimer's disease

Alzheimer's disease (AD) is characterized by neurotoxic amyloid-ß plaque formation in brain parenchyma and cerebral blood vessels known as cerebral amyloid angiopathy (CAA). Besides CAA, AD is strongly related to vascular diseases such as stroke and atherosclerosis. Cerebrovascular dysfunction occurs in AD patients leading to alterations in blood flow that might play an important role in AD pathology with neuronal loss and memory deficits. Platelets are the major players in hemostasis and thrombosis, but are also involved in neuroinflammatory diseases like AD. For many years, platelets were accepted as peripheral model to study the pathophysiology of AD because platelets display the enzymatic activities to generate amyloid-ß (Aß) peptides. In addition, platelets are considered to be a biomarker for early diagnosis of AD. Effects of Aß peptides on platelets and the impact of platelets in the progression of AD remained, however, ill-defined. The present study explored the cellular mechanisms triggered by Aß in platelets. Treatment of platelets with Aß led to platelet activation and enhanced generation of reactive oxygen species (ROS) and membrane scrambling, suggesting enhanced platelet apoptosis. More important, platelets modulate soluble Aß into fibrillar structures that were absorbed by apoptotic but not vital platelets. This together with enhanced platelet adhesion under flow ex vivo and in vivo and platelet accumulation at amyloid deposits of cerebral vessels of AD transgenic mice suggested that platelets are major contributors of CAA inducing platelet thrombus formation at vascular amyloid plaques leading to vessel occlusion critical for cerebrovascular events like stroke.

Plasma beta-amyloid and white matter lesions in AD, MCI, and cerebral amyloid angiopathy

BACKGROUND

Microvascular brain injury, typically measured by extent of white matter hyperintensity (WMH) on MRI, is an important contributor to cognitive impairment in the elderly. Recent studies suggest a role for circulating beta-amyloid peptide in microvascular dysfunction and white matter disease.

METHODS

The authors performed a cross-sectional study of clinical, biochemical, and genetic factors associated with WMH in 54 subjects with Alzheimer disease (AD) or mild cognitive impairment (AD/MCI) and an independent group of 42 subjects with cerebral amyloid angiopathy (CAA). Extent of WMH was determined by computer-assisted volumetric measurement normalized to intracranial size (nWMH). Biochemical measurements included plasma concentrations of the 40- and 42-amino acid species of beta-amyloid (Abeta40 and Abeta42) detected by specific enzyme-linked immunosorbent assays.

RESULTS

Plasma Abeta40 concentrations were associated with nWMH in both groups (correlation coefficient = 0.48 in AD/MCI, 0.42 in CAA, p < or = 0.005). Plasma Abeta40 remained independently associated with nWMH after adjustment for potential confounders among age, hypertension, diabetes, homocysteine, creatinine, folate, vitamin B12, and APOE genotype. The presence of lacunar infarctions was also associated with increased Abeta40 in both groups. nWMH was greater in CAA (19.8 cm3) than AD (11.1 cm3) or MCI (10.0 cm3; p < 0.05 for both comparisons).

CONCLUSIONS

Plasma beta-amyloid 40 concentration is independently associated with extent of white matter hyperintensity in subjects with Alzheimer disease, mild cognitive impairment, or cerebral amyloid angiopathy. If confirmed in longitudinal studies, these data would suggest circulating beta-amyloid peptide as a novel biomarker or risk factor for microvascular damage in these common diseases of the elderly.

Association of homocysteine with plasma amyloid β protein in aging and neurodegenerative disease

BACKGROUND

Elevated plasma total homocysteine (tHcy) is a risk factor for cardiovascular disease and is reported to be an independent risk factor for Alzheimer disease (AD) and cognitive decline. tHcy may potentiate neurotoxic and vasculopathic processes, including amyloid beta protein (Abeta) metabolism, implicated in neurodegenerative diseases.

OBJECTIVE

To examine the relationship of plasma total tHcy levels with clinical, demographic, biochemical, and genetic factors in aging, mild cognitive impairment (MCI), AD, cerebral amyloid angiopathy (CAA), and Parkinson disease (PD).

METHODS

Plasma tHcy, folate, vitamin B(12), creatinine, and Abeta levels were assessed in individuals evaluated in the Memory, Stroke, and Movement Disorders Units of Massachusetts General Hospital with diagnoses of AD (n = 145), MCI (n = 47), PD (n = 93), CAA (67), hypertensive intracerebral hemorrhage (hICH) (n = 25), and no dementia (n = 88).

RESULTS

The tHcy levels did not differ across AD, MCI, CAA, hICH, and nondemented control subjects but were increased in the PD group (p < 0.01). The elevated levels within the PD group were due to high tHcy in individuals taking levodopa (p < 0.0001). Increasing tHcy was associated with worse cognition in the PD cases, but not the other diagnostic groups. tHcy levels positively correlated with plasma Abeta levels even after adjustments for age and creatinine (p < 0.0001).

CONCLUSIONS

Mean tHcy levels increased with age but did not discriminate diagnostic groups aside from significant elevation in patients with PD taking levodopa. The positive association between tHcy and plasma Abeta levels raises the possibility that these circulating factors could interact to affect AD risk and cognition in PD.

Circulating amyloid-beta peptide crosses the blood-brain barrier in aged monkeys and contributes to Alzheimer's disease lesions

1. We studied cerebrovascular sequestration and blood-brain barrier (BBB) permeability to [125I]- or [123I]-labeled amyloid-beta peptides (A beta) in aged rhesus and aged squirrel monkey, the nonhuman primate models of cerebral beta-amyloidosis and cerebrovascular amyloid angiopathy (CAA), respectively. 2. In aged rhesus, the half-time of elimination of [125I]A beta 1-40, t1/2e, was faster by 1.34 h, the systemic clearance, Clss, increased by 4.21 ml/min/kg and the mean residence time of intact peptide in the circulation shortened by 2 h. 3. Cerebrovascular sequestration of [125I]A beta 1-40 was significant in aged squirrel monkey (20.8 ml/g x 10(2)), but undetectable in the rhesus. 4. The permeability surface area product, PS, for [14C]inulin was low in both species (0.11-0.18 ml/g/s x 10(6)) indicating an intact barrier. 5. The BBB permeability to A beta 1-40 was 34.8- and 13.7-fold higher than for [14C]inulin in aged squirrel and rhesus, respectively, suggesting a specialized A beta transport across the BBB. 6. The single photon computed emission tomography studies confirmed a saturable [123I]A beta 1-40 transport at the BBB in primates (Km = 40 nM). 7. Brain autoradiographic analysis of [125I]A beta 1-42 or [125I]A beta 1-40 after intracarotid infusions of radiotracers confirmed co-localization of the signal with A beta-immunoreactive plaques in rhesus monkeys. 8. Metabolism of [125I]A beta 1-40 in brain and plasma was slower in aged squirrel compared to aged rhesus, by 2.9- and 2.6-fold, respectively. 9. Thus, transport of circulating A beta across the BBB contributes to brain parenchymal accumulation of amyloid in aged nonhuman primates. Negligible capillary binding, rapid systemic and brain degradation, and accelerated body elimination of blood-borne A beta, may prevent the development of CAA in rhesus in contrast to squirrel monkeys.

Novel ABCA1 compound variant associated with HDL cholesterol deficiency

The recent discovery of an ATP-binding cassette transporter, ABCA1, as an important regulator of high density lipoprotein (HDL) metabolism and reverse cholesterol transport has facilitated the identification of novel variants associated with HDL cholesterol deficiency states. We identified a subject with HDL cholesterol deficiency (4 mg/dl) who developed and died of complications related to cerebral amyloid angiopathy (CAA). The proband had a compound heterozygous mutation. One mutation was a G3295T substitution with conversion of asparagine to tyrosine (D1099Y) in ABCA1. The single-base substitution at codon 1099 resulted in the abolition of an RsaI cleavage site. The proband and affected individuals having another mutation were heterozygotes for T5966C with phenylalanine converted to serine (F2009S). The presence of the T5966C mutation was detected by restriction digestion with HinfI. These variants were not identified in over 400 chromosomes of healthy subjects. In the kindred, family members heterozygous for the ABCA1 variant exhibited low levels of HDL cholesterol. Direct sequencing of all coding regions and splice site junctions of other HDL candidate genes revealed no additional mutations, indicating that combined defective ABCA1 alleles may result in familial HDL deficiency.

The cerebral hemorrhage-producing cystatin C variant (L68Q) in extracellular fluids

A variant of the normal extracellular cysteine protease inhibitor cystatin C (L68Q-cystatin C), is the amyloid precursor in hereditary cystatin C amyloid angiopathy (HCCAA). It has been suggested that the mutation causes cellular entrapment of L68Q-cystatin C in vivo and that the variant protein is not secreted to extracellular fluids. In order to test this hypothesis, we used matrix-assisted laser desorption ionization time-of-flight mass spectrometry in an effort to demonstrate the presence of L68Q- along with wildtype cystatin C in plasma and cerebrospinal fluid (CSF) of HCCAA-patients. Plasma from all five investigated HCCAA-patients contained both L68Q- and wildtype cystatin C. The presence of approximately equal amounts of cystatin C dimers and monomers was demonstrated in plasma from HCCAA-patients, whereas only monomers could be found in normal plasma. L68Q-wildtype-cystatin C heterodimers seem to be present in the dimeric cystatin C population. CSF from six HCCAA-patients also contained cystatin C-dimers and monomers, but the dimeric fraction was minute. CSF from control patients did not contain dimeric cystatin C. These results suggest that the milieu of L68Q-cystatin C is important for its stability and dimerization status and that certain milieus might hinder its further development into oligomers, amyloid fibrils and other precipitating aggregates.

Plasma beta-amyloid peptide, transforming growth factor-beta 1, and risk for cerebral amyloid angiopathy

Despite the documented association between apolipoprotein E genotype and cerebral amyloid angiopathy (CAA), a substantial proportion of CAA-related hemorrhages occur in patients without known risks for this disorder. Two other factors implicated in the pathogenesis of CAA are the amyloid-beta peptide (preferentially deposited in vessels as a 40-amino acid species) and the multifunctional cytokine transforming growth factor-beta 1 (a specific promoter of vascular amyloid deposition in transgenic models). We measured plasma concentrations of these factors in a series of 25 patients diagnosed with probable or definite CAA-related hemorrhage and compared them with 21 patients with hemorrhage due to probable hypertensive vasculopathy and 42 elderly control subjects without hemorrhage. We found no differences among the groups in concentrations of the 40- or 42-amino acid species of beta-amyloid or either the active or latent form of transforming growth factor-beta 1. While the data do not exclude important roles for these molecules as risks for CAA, they indicate that plasma measurements are not useful in its diagnosis.

Hereditary cystatin C amyloid angiopathy: monitoring the presence of the Leu-68-->Gln cystatin C variant in cerebrospinal fluids and monocyte cultures by MS

Hereditary cystatin C amyloid angiopathy (HCCAA) is an autosomal dominant condition in which the patients suffer at an early age from repeated cerebral haemorrhages. The development of HCCAA is directly linked to a Leu-68-->Gln (L68Q) mutation in the cystatin C protein sequence. The concentration of cystatin C in cerebrospinal fluid (CSF) of HCCAA patients is markedly diminished and cultivated monocytes from affected individuals accumulate cystatin C. The goal of this work was to characterize cystatin C isolated from CSF and monocyte cultures originating from healthy persons and HCCAA patients with respect to the L68Q mutation. Cystatin C was isolated by carboxymethylpapain affinity chromatography. Proteins from CSF and monocyte cultures that bound specifically to the carboxymethylated papain column were resolved by reverse-phase HPLC chromatography and tryptic peptides were subsequently analysed by matrix-assisted laser desorption ionization MS. No evidence for mutated cystatin C protein was found in CSF samples from healthy subjects or HCCAA patients, but approx. 60% of the protein was found to be hydroxylated on Pro-3. No evidence was found for secretion of mutated cystatin C from HCCAA monocytes. However, we obtained evidence for the presence of mutated cystatin C in HCCAA monocytes. These results support the conclusion that the mutated cystatin C is retained in association with the monocytes and not secreted. An increased intracellular concentration would presumably promote the aggregation and denaturation of the mutated cystatin C, leading to the formation of amyloid fibrils and cell death.

Cerebrovascular accumulation and increased blood-brain barrier permeability to circulating Alzheimer's amyloid beta peptide in aged squirrel monkey with cerebral amyloid angiopathy

Senescent squirrel monkey is a valuable model to study pathogenesis of cerebrovascular amyloid angiopathy (CAA). Cerebrovascular sequestration and blood-brain barrier (BBB) permeability to 121I-amyloid beta(1-40) synthetic peptide (sA beta(1-40)) were studied in adult versus aged squirrel monkey 1 h after a single intravenous injection. In aged monkey, the half-time of elimination of sA beta(1-40), t(1/2)e, was prolonged by 0.6 h, the systemic clearance, ClSS, was reduced from 1.8 to 1.1 ml/min/kg, and the mean residence time of intact peptide in the circulation was increased by 1 h (45%). In adult monkey, cerebrovascular sequestration of intact sA beta(1-40) was significant, and the BBB permeability was 18.6-fold higher than for inulin. In aged monkey, the sequestration of intact sA beta(1-40) by cortical and leptomeningeal microvessels and the BBB permeability were increased by 5.9, 1.8-, and 2.1-fold, respectively, in the presence of an unchanged barrier to inulin. In brain parenchyma of aged animals, 76.1% of circulating sA beta(1-40) remained intact versus 45.7% in adult. We conclude that multiple age-related systemic effects, i.e., reduced body elimination and systemic clearance of sA beta(1-40), and reduced peripheral metabolism, may act in concert with BBB mechanisms, i.e., increased transendothelial transport and microvascular accumulation of blood-borne sA beta(1-40), and reduced brain metabolism to enhance the development of CAA.

On the role of monocytes/macrophages in the pathogenesis of central nervous system lesions in hereditary cystatin C amyloid angiopathy

The pathogenesis of the deposition of a variant cystatin C as amyloid in hereditary cystatin C amyloid angiopathy (HCCAA) is not known. To address this question the synthesis and secretion of cystatin C in cultured monocytes from 9 carriers of the mutated cystatin C gene (5 symptomatic and 4 asymptomatic) was examined. The quantity of cystatin C in cells and supernatants was determined by the ELISA method, Western blots were done and selected samples immunostained for cystatin C. Monocytes from individuals carrying the gene defect synthesized cystatin C that was apparently not truncated, a form found in the cerebral amyloid deposits in HCCAA, but showed a distinctly lower rate of cystatin C synthesis than monocytes from healthy controls. The main difference was that the quantity of cystatin C was significantly lower in the supernatants in monocyte cultures from carriers of the gene defect than from healthy controls, possibly due to a partial block in its secretion. This abnormal processing of the cystatin C could explain the low cerebrospinal fluid levels of cystatin C in HCCAA and might be a part of the pathogenetic pathway of amyloid deposition. Furthermore it could, through a lower extracellular concentration of this inhibitor of cysteine proteinases, contribute to destruction of the amyloidotic blood vessels, leading to the most serious clinical manifestation in HCCAA, intracerebral hemorrhage.