Induction of vascular amyloidosis-β by oxidative stress depends on APOE genotype

Capillary CAA and perivascular Aβ-deposition: two distinct features of Alzheimer's disease pathology

Cerebral amyloid angiopathy (CAA) is frequently seen in Alzheimer's disease (AD) cases and represents one of its histopathological hallmarks. CAA is characterized by amyloid β-protein (Aβ) deposits within vessel walls. In addition to arteries and veins capillaries can also be affected. Aβ deposition into the capillary wall is, thereby, known as capillary CAA (capCAA) and strongly associated with the apolipoprotein E APOEε4 allele as a risk factor. Aβ deposits along the pericapillary glia limitans are described as pericapillary Aβ (pericapAβ: synonymous with pericapillary CAA in other studies). Here, we studied the relationship between pericapAβ and capCAA in 58 human autopsy cases. Although pericapAβ and capCAA were more frequently found in AD cases compared to controls and although they exhibited a correlation to one another, detailed analysis revealed that there is a significant number of cases with pericapAβ lacking capCAA and vice versa. Moreover, single capillaries show either both pathologies or pericapAβ or capCAA only. There was no local association between these pathologies when analyzing multiple capillaries in each given case. Moreover, pericapAβ predominantly exhibited Aβ(42) whereas capCAA contained both Aβ(42) and Aβ(40). These differences as well as differences in the related astroglial reaction indicate that pericapAβ and capCAA are not directly linked. PericapAβ appears to represent initial Aβ accumulation along the glia limitans that is involved in the perivascular drainage of apoE and Aβ regardless of the APOE genotype whereas capCAA could be explained by a limited transendothelial clearance of apoE4-Aβ complexes compared to apoE2/3-Aβ complexes.

Transferrin and HFE genes interact in Alzheimer's disease risk: the Epistasis Project

Iron overload may contribute to the risk of Alzheimer's disease (AD). In the Epistasis Project, with 1757 cases of AD and 6295 controls, we studied 4 variants in 2 genes of iron metabolism: hemochromatosis (HFE) C282Y and H63D, and transferrin (TF) C2 and -2G/A. We replicated the reported interaction between HFE 282Y and TF C2 in the risk of AD: synergy factor, 1.75 (95% confidence interval, 1.1-2.8, p = 0.02) in Northern Europeans. The synergy factor was 3.1 (1.4-6.9; 0.007) in subjects with the APOEε4 allele. We found another interaction, between HFE 63HH and TF -2AA, markedly modified by age. Both interactions were found mainly or only in Northern Europeans. The interaction between HFE 282Y and TF C2 has now been replicated twice, in altogether 2313 cases of AD and 7065 controls, and has also been associated with increased iron load. We therefore suggest that iron overload may be a causative factor in the development of AD. Treatment for iron overload might thus be protective in some cases.

Vascular pathology in the aged human brain

Cerebral atherosclerosis (AS), small vessel disease (SVD), and cerebral amyloid angiopathy (CAA) are the most prevalent arterial disorders in the aged brain. Pathogenetically, AS and SVD share similar mechanisms: plasma protein leakage into the vessel wall, accumulation of lipid-containing macrophages, and fibrosis of the vessel wall. CAA, on the other hand, is characterized by the deposition of the amyloid β-protein in the vessel wall. Despite these differences between CAA, AS and SVD, apolipoprotein E (apoE) is involved in all three disorders. Such a pathogenetic link may explain the correlations between AS, SVD, CAA, and Alzheimer’s disease in the brains of elderly individuals reported in the literature. In addition, AS, SVD, and CAA can lead to tissue lesions such as hemorrhage and infarction. Moreover, intracerebral SVD leads to plasma protein leakage into the damaged vessel wall and into the perivascular space resulting in a blood–brain barrier (BBB) dysfunction. This SVD-related BBB dysfunction is considered to cause white matter lesions (WMLs) and lacunar infarcts. In this review, we demonstrate the relationship between AS, SVD, and CAA as well as their contribution to the development of vascular tissue lesions and we emphasize an important role for apoE in the pathogenesis of vessel disorders and vascular tissue lesions as well as for BBB dysfunction on WML and lacunar infarct development.

Modulating effect of apolipoprotein E polymorphisms on secondary brain insult and outcome after childhood brain trauma

OBJECTIVE

The aim of this study was to determine the relationship between apolipoprotein E (APO E) alleles, the amount of cerebral perfusion pressure (CPP) insult and outcome in children after brain trauma.

MATERIALS AND METHODS

In a prospective two-centre case-control study, the APO E genotypes of 65 critically ill children admitted after brain trauma were correlated with age-related CPP insult quantification, conscious state at the time of discharge from intensive care and global outcome at 6 months post-injury. One hundred sixty healthy age- and sex-matched children were genotyped as controls.

RESULTS

The CPP insult level among the e4 carriers with poor outcome was significantly less than the non-e4 carriers (p=0.03). Homozygotic e3 patients with good recovery did so despite having suffered nearly 26 times more CPP insult than those who were not e3 homzygous (p=0.02).

CONCLUSION

Different APO E alleles may potentially affect cerebral ischaemic tolerance differently in children after brain trauma.

Cerebral amyloid angiopathy and its relationship to Alzheimer's disease

Cerebral amyloid angiopathy (CAA) is characterized by the deposition of the amyloid beta-protein (A beta) within cerebral vessels. The involvement of different brain areas in CAA follows a hierarchical sequence similar to that of Alzheimer-related senile plaques. Alzheimer's disease patients frequently exhibit CAA. The expansion of CAA in AD often shows the pattern of full-blown CAA. The deposition of A beta within capillaries distinguishes two types of CAA. One with capillary A beta-deposition is characterized by a strong association with the apolipoprotein E (APOE) epsilon 4 allele and by its frequent occurrence in Alzheimer's disease cases whereas the other one lacking capillary A beta-deposits is not associated with APOE epsilon 4. Capillary CAA can be seen in every stage of CAA or AD-related A beta-deposition. AD cases with capillary CAA show more widespread capillary A beta-deposition than non-demented cases as well as capillary occlusion. In a mouse model of CAA, capillary CAA was associated with capillary occlusion and cerebral blood flow disturbances. Thus, blood flow alterations with subsequent hypoperfusion induced by CAA-related capillary occlusion presumably point to a second mechanism in which A beta adversely affects the brain in AD in addition to its direct neurotoxic effects.

Association between enzymatic and non-enzymatic antioxidant defense mechanism with apolipoprotein E genotypes in Alzheimer disease

OBJECTIVE

There are evidence suggesting that APOE-varepsilon4 allele play an important role in the pathogenesis of Alzheimer's disease (AD) by reducing peripheral levels and activities of a broad spectrum of nonenzymatic and enzymatic antioxidants systems. However, the link between APOE genotype, oxidative stress, and AD has yet to be established. In this study we examined whether antioxidant defense mechanism exacerbates the risk of AD in individual carrying APOE-varepsilon4 allele in a population from Tehran, Iran.

METHOD

We determined the enzymatic activities of the erythrocyte Cu-Zn superoxide dismutase (Cu-Zn SOD), glutathione peroxidase (GSH-Px), catalase (CAT) and serum level of total antioxidant status(TAS) in various APOE genotypes in 91 patients with AD and 91 healthy subjects as control group (age and sex-matched).

RESULT

The results showed that the TAS level and the activities of enzymatic antioxidants CAT and GSH-Px were significantly lower and the SOD activity was significantly higher in AD patients compared to controls. The AD patients with APOE-varepsilon4 allele genotype had significantly lower serum TAS concentration and lower erythrocytes GSH-Px and CAT activities (p=0.001) but significantly higher erythrocytes Cu-Zn SOD activity (p=0.001) than the non-APOE-varepsilon4 carrier AD and the control group. In addition, the association observed between the factors involved in an antioxidant defense mechanism and APOE-varepsilon4 allele in AD increased with age of the subjects.

CONCLUSION

These data indicate that the reduced serum level of TAS and activity of CAT, GSH-Px and increased SOD exacerbate the risk of AD in individuals carrying APOE-varepsilon4 allele. The reduced antioxidants defense in APOE-varepsilon4 allele carrier may contribute to beta-amyloidosis. This effect, however, is more pronounced in the AD patients older than 75 years of age. This suggests that a therapeutic modality should be considered for these subjects.

Diurnal variations in salivary protein carbonyl levels in normal and cognitively impaired human subjects

Oxidative stress has been documented in tissues and biofluids of subjects with sporadic Alzheimer disease (AD) and mild cognitive impairment (MCI). The aim of this study was to determine whether (a) salivary protein carbonyls are elevated in AD and MCI subjects, (b) salivary protein carbonyl contents in these groups exhibit diurnal variation, and (c) apolipoprotein E epsilon 4 (apoE epsilon 4) carrier status impacts salivary carbonyl concentrations or rhythmicity in the AD and MCI cohorts. Unstimulated saliva was collected at fixed intervals between 8 AM: and 10 PM: from 15 AD subject , 21 MCI subjects, and 30 cognitively-intact controls. Salivary protein carbonyl concentrations were measured by ELISA. ApoE genotyping was performed on the AD and MCI individuals. For all groups, mean protein carbonyl contents were significantly elevated at 2 PM: relative to other time points surveyed. Mean salivary protein carbonyl concentrations did not differ among the diagnostic groups. ApoE epsilon 4 carriers exhibited less temporal variation in salivary protein carbonyls relative to noncarriers. Thus, protein carbonyl content exhibits diurnal variation in adult human saliva. ApoE epsilon 4 carrier status may impact oropharyngeal disease expression by attenuating the inherent diurnal variability in salivary redox homeostasis. Salivary protein carbonyls do not differentiate AD and MCI from normal individuals. In conclusion, oxidative stress has been documented in tissues and biofluids of subjects with sporadic AD and MCI. This article demonstrates that levels of protein carbonyls, a marker of oxidative stress, exhibit robust diurnal variation in the saliva of normal elderly, MCI, and AD subjects. Apolipoprotein E epsilon 4 allele carrier status may attenuate this temporal variability in salivary redox homeostasis and thereby impact the natural history of oropharyngeal diseases.

Neprilysin protects human neuronal progenitor cells against impaired development caused by amyloid-β peptide

Transplantation of human neuronal progenitor cells (HNPC) is being considered for neuroreplacement therapy in beta-amyloidosis associated with neuronal loss in Down's syndrome and Alzheimer's disease. However, the influence of amyloid-beta-containing brain environment on the development of HNPCs is unknown. Recently, we demonstrated that amyloid-beta peptide (Abeta) impaired differentiation of HNPCs in culture through oxidative stress. Now we studied the effect of neprilysin, an Abeta-degrading enzyme, on development of neuronal colonies from neurospheres of HNPCs in the presence of Abeta1-40. Neprilysin increased the number of neurospheres that formed colonies of neuron-like cells. This effect of neprilysin was associated with reduced amounts of the monomeric and dimeric Abeta that remained in culture supernatants as well as the Abeta uptaken by differentiating HNPCs. Phosphoramidon, a neprilysin inhibitor, attenuated these effects of neprilysin. In control cultures of HNPCs that grew without exogenous Abeta1-40, the treatment with neprilysin reduced the number of developing colonies. This effect might result from degradation by neprilysin of endogenous Abeta produced and secreted by HNPCs or other peptides that are involved in neuronal development. The results demonstrate that even a partial reduction of extracellular Abeta levels by neprilysin may facilitate development of HNPCs into neurons in an environment overloaded with Abeta. This finding suggests that neprilysin could facilitate neuroreplacement therapy with HNPCs in treatment of neurodegenerative diseases.

Occurrence and co-localization of amyloid beta-protein and apolipoprotein E in perivascular drainage channels of wild-type and APP-transgenic mice

The deposition of the amyloid beta-protein (Abeta) is a hallmark of Alzheimer's disease (AD). One reason for Abeta-accumulation and deposition in the brain may be an altered drainage along perivascular channels. Extracellular fluid is drained from the brain towards the cervical lymph nodes via perivascular channels. The perivascular space around cerebral arteries is the morphological correlative of these drainage channels. Here, we show that Abeta is immunohistochemically detectable within the perivascular space of 25 months old wild-type and amyloid precursor protein (APP)-transgenic mice harboring the Swedish double mutation driven by a neuron specific promoter. Only small amounts of Abeta can be detected immunohistochemically in the perivascular space of wild-type mice. Cerebrovascular and parenchymal Abeta-deposits were absent. In APP-transgenic mice, large amounts of Abeta were found in the perivascular drainage channels accompanied with cerebrovascular and parenchymal Abeta-deposition. The apolipoprotein E (apoE) immunostaining within the perivascular channels did not vary between wild-type and APP-transgenic mice. Almost 100% of the area that represents the perivascular space was stained with an antibody directed against apoE. Here, Abeta co-localized with apoE indicating an involvement of apoE in the perivascular clearance of Abeta. Fibrillar congophilic amyloid was not seen in wild-type mice. In APP-transgenic animals, congophilic fibrillar amyloid material was seen in the wall of cerebral blood vessels but not in the perivascular space. In conclusion, our results suggest that non-fibrillar forms of Abeta are drained along perivascular channels and that apoE is presumably involved in this clearance mechanism. Overloading such a clearance mechanism in APP-transgenic mice appears to result in insufficient Abeta-clearance, increased Abeta-levels in the brain and the perivascular drainage channels, and finally in Abeta-deposition. In so doing, our results strengthen the hypothesis that an alteration of perivascular drainage supports Abeta-deposition and the development of AD.

Reduction in mitochondrial superoxide dismutase modulates Alzheimer's disease-like pathology and accelerates the onset of behavioral changes in human amyloid precursor protein transgenic mice

Alzheimer's disease (AD) is associated with accumulations of amyloid-beta (Abeta) peptides, oxidative damage, mitochondrial dysfunction, neurodegeneration, and dementia. The mitochondrial antioxidant manganese superoxide dismutase-2 (Sod2) might protect against these alterations. To test this hypothesis, we inactivated one Sod2 allele (Sod2(+/-)) in human amyloid precursor protein (hAPP) transgenic mice, reducing Sod2 activity to approximately 50% of that in Sod2 wild-type (Sod2(+/+)) mice. A reduction in Sod2 activity did not obviously impair mice without hAPP/Abeta expression. In hAPP mice, however, it accelerated the onset of behavioral alterations and of deficits in prepulse inhibition of acoustic startle, a measure of sensorimotor gating. In these mice, it also worsened hAPP/Abeta-dependent depletion of microtubule-associated protein 2, a marker of neuronal dendrites. Sod2 reduction decreased amyloid plaques in the brain parenchyma but promoted the development of cerebrovascular amyloidosis, gliosis, and plaque-independent neuritic dystrophy. Sod2 reduction also increased the DNA binding activity of the transcription factor nuclear factor kappaB. These results suggest that Sod2 protects the aging brain against hAPP/Abeta-induced impairments. Whereas reductions in Sod2 would be expected to trigger or exacerbate neuronal and vascular pathology in AD, increasing Sod2 activity might be of therapeutic benefit.