Unifying features of systemic and cerebral amyloidosis

Current and future treatment of amyloid diseases

There are more than 30 human proteins whose aggregation appears to cause degenerative maladies referred to as amyloid diseases or amyloidoses. These disorders are named after the characteristic cross-β-sheet amyloid fibrils that accumulate systemically or are localized to specific organs. In most cases, current treatment is limited to symptomatic approaches and thus disease-modifying therapies are needed. Alzheimer's disease is a neurodegenerative disorder with extracellular amyloid β-peptide (Aβ) fibrils and intracellular tau neurofibrillary tangles as pathological hallmarks. Numerous clinical trials have been conducted with passive and active immunotherapy, and small molecules to inhibit Aβ formation and aggregation or to enhance Aβ clearance; so far such clinical trials have been unsuccessful. Novel strategies are therefore required and here we will discuss the possibility of utilizing the chaperone BRICHOS to prevent Aβ aggregation and toxicity. Type 2 diabetes mellitus is symptomatically treated with insulin. However, the underlying pathology is linked to the aggregation and progressive accumulation of islet amyloid polypeptide as fibrils and oligomers, which are cytotoxic. Several compounds have been shown to inhibit islet amyloid aggregation and cytotoxicity in vitro. Future animal studies and clinical trials have to be conducted to determine their efficacy in vivo. The transthyretin (TTR) amyloidoses are a group of systemic degenerative diseases compromising multiple organ systems, caused by TTR aggregation. Liver transplantation decreases the generation of misfolded TTR and improves the quality of life for a subgroup of this patient population. Compounds that stabilize the natively folded, nonamyloidogenic, tetrameric conformation of TTR have been developed and the drug tafamidis is available as a promising treatment.

The proteome response to amyloid protein expression in vivo

Protein misfolding disorders such as Alzheimer, Parkinson and transthyretin amyloidosis are characterized by the formation of protein amyloid deposits. Although the nature and location of the aggregated proteins varies between different diseases, they all share similar molecular pathways of protein unfolding, aggregation and amyloid deposition. Most effects of these proteins are likely to occur at the proteome level, a virtually unexplored reality. To investigate the effects of an amyloid protein expression on the cellular proteome, we created a yeast expression system using human transthyretin (TTR) as a model amyloidogenic protein. We used Saccharomyces cerevisiae, a living test tube, to express native TTR (non-amyloidogenic) and the amyloidogenic TTR variant L55P, the later forming aggregates when expressed in yeast. Differential proteome changes were quantitatively analyzed by 2D-differential in gel electrophoresis (2D-DIGE). We show that the expression of the amyloidogenic TTR-L55P causes a metabolic shift towards energy production, increased superoxide dismutase expression as well as of several molecular chaperones involved in protein refolding. Among these chaperones, members of the HSP70 family and the peptidyl-prolyl-cis-trans isomerase (PPIase) were identified. The latter is highly relevant considering that it was previously found to be a TTR interacting partner in the plasma of ATTR patients but not in healthy or asymptomatic subjects. The small ubiquitin-like modifier (SUMO) expression is also increased. Our findings suggest that refolding and degradation pathways are activated, causing an increased demand of energetic resources, thus the metabolic shift. Additionally, oxidative stress appears to be a consequence of the amyloidogenic process, posing an enhanced threat to cell survival.

Diffuse metabolic changes in the brain of patients with familial amyloid polyneuropathy. A proton MRSI study

OBJECTIVES

To assess brain metabolic abnormalities in patients with familial amyloid polyneuropathy (FAP) due to the transthyretin (TTR) gene mutations.

BACKGROUND

The TTR-FAP has variable phenotypic expression, which includes abnormalities of the central nervous system (CNS). Several conventional MRI studies have shown brain abnormalities, probably secondary to amyloid accumulation in leptomeningeal and subarachnoid vessels. However, TTR-related amyloid deposits do not seem to significantly affect the brain parenchyma and a prominent CNS impairment is considered to be rare in TTR amyloidosis.

METHODS

We performed proton MR spectroscopic imaging (1H-MRSI) in the central brain of four unrelated TTR-FAP patients with either minimal or no signs of neurological involvement and eight age- and sex-matched normal controls (NC). Metabolic changes were assessed in the entire volume of interest (VOI) and in the frontal, periventricular and posterior white matter (WM).

RESULTS

Conventional MRI was normal in 2 patients and showed minimal WM lesions in the remaining 2 patients. 1H-MRSI showed N-acetylaspartate to creatine ratio (NAA/Cr) decreases in the central brain VOI in all TTR-FAP patients (p < 0.005). These NAA/Cr decreases were homogeneous in all WM regions (p < 0.05 for all).

CONCLUSIONS

1H-MRSI findings suggest that diffuse metabolic changes, probably related to axonal damage, are present in brains of TTR-FAP patients even when they have no or minimal clinical and MRI signs of CNS involvement. The mechanism leading to sub-clinical metabolic brain changes needs to be identified.

Sporadic and familial cerebral amyloid angiopathies

Cerebral amyloid angiopathy (CAA) is the term used to describe deposition of amyloid in the walls of arteries, arterioles and, less often, capillaries and veins of the central nervous system. CAAs are an important cause of cerebral hemorrhage and may also result in ischemic lesions and dementia. A number of amyloid proteins are known to cause CAA. The most common sporadic CAA, caused by A beta deposition, is associated with aging and is a common feature of Alzheimer disease (AD). CAA occurs in several familial conditions, including hereditary cerebral hemorrhage with amyloidosis of Icelandic type caused by deposition of mutant cystatin C, hereditary cerebral hemorrhage with amyloidosis Dutch type and familial AD with deposition of either A beta variants or wild-type A beta, the transthyretin-related meningo-vascular amyloidoses, gelsolin as well as familial prion disease-related CAAs and the recently described BRI2 gene-related CAAs in familial British dementia and familial Danish dementia. This review focuses on the morphological, biochemical, and genetic aspects as well as the clinical significance of CAAs with special emphasis on the BRI2 gene-related cerebrovascular amyloidoses. We also discuss data relevant to the pathomechanism of the different forms of CAA with an emphasis on the most common A beta-related types.

Argpyrimidine, a methylglyoxal-derived advanced glycation end-product in familial amyloidotic polyneuropathy

FAP (familial amyloidotic polyneuropathy) is a systemic amyloid disease characterized by the formation of extracellular deposits of transthyretin. More than 80 single point mutations are associated with amyloidogenic behaviour and the onset of this fatal disease. It is believed that mutant forms of transthyretin lead to a decreased stability of the tetramer, which dissociates into monomers that are prone to unfolding and aggregation, later forming beta-fibrils in amyloid deposits. This theory does not explain the formation of beta-fibrils nor why they are toxic to nearby cells. Age at disease onset may vary by decades for patients with the same mutation. Moreover, non-mutated transthyretin also forms the same deposits in SSA (senile systemic amyloidosis), suggesting that mutations may only accelerate this process, but are not the determinant factor in amyloid fibril formation and cell toxicity. We propose that glycation is involved in amyloidogenesis, since amyloid fibrils present several properties common to glycated proteins. It was shown recently that glycation causes the structural transition from the folded soluble form to beta-fibrils in serum albumin. We identified for the first time a methylglyoxal-derived advanced glycation end-product, argpyrimidine [N(delta)-(5-hydroxy-4,6-dimethylpyrimidin-2-yl)-L-ornithine] in amyloid fibrils from FAP patients. Unequivocal argpyrimidine identification was achieved chromatographically by amino acid analysis using dabsyl (4-dimethylaminoazobenzene-4'-sulphonyl) chloride. Argpyrimidine was found at a concentration of 162.40+/-9.05 pmol/mg of protein in FAP patients, and it was not detected in control subjects. The presence of argpyrimidine in amyloid deposits from FAP patients supports the view that protein glycation is an important factor in amyloid diseases.

Effects of apolipoprotein E genotypes on the development of exfoliation syndrome

Apolipoprotein E (apo E) is directly involved in the amyloid deposition and fibril formation and is present in many cerebral and systemic amyloidoses immunologically. It is encoded by a polymorphic gene and it has three common alleles-epsilon2, epsilon3, and epsilon4. Exfoliation syndrome (XFS) is characterized by the deposition throughout the body of focal fibrillogranular aggregates in which there have been some reports of amyloid or amyloid-like features. We evaluated the possible association between apo E polymorphism and the occurrence of XFS. Using High Pure PCR Template Preparation Kits, genomic DNAs were extracted from whole blood and apo E polymorphisms were determined by using Lightcycler-Apo E Mutation Detection Kits in 76 patients with XFS and 74 controls. The E2/E2, E2/E3 and E2/E4 genotypes (OR 29.9, 95% CI 3.1-293.7; OR 56.1, 95% CI 12.5-252.7; OR 43.9, 95% CI 7.4-257.6, respectively) and the in2 allele are found to have an increased risk of developing XFS (p=0.0001); whereas the in3 allele was found to be protective (p=0.0001). Apo E polymorphism and the presence of in2 allele are seem to be significantly associated with the development of XFS.

Immunohistochemical study of distribution of apolipoproteins E and D in human cerebral beta amyloid deposits

Several molecules are known to be closely associated with amyloid deposits in human brain. Among these, apolipoproteins such as apolipoproteins E (apo E) and J (apo J) have been found in two neuropathological hallmarks of Alzheimer's disease (AD) and cerebral amyloid angiopathy (CAA): senile plaques (SPs) and cerebrovascular amyloid. These apolipoproteins may be implicated in amyloid fibrillogenesis. Apo D is a multiligand-multifunctional glycoprotein present in SPs, as we previously reported. The aim of this work is to study the link between immunolocalization of apo E and apo D in AD and CAA brains. Both apolipoproteins were found in all types of SPs, but apo E was observed more often than apo D in mature plaques. Whereas apo E is always located overlapping the amyloid core, apo D seems to situate preferably around and near the amyloid. Immunohistochemistry revealed that these apolipoproteins behave differently in cerebral vessels. Apo E labeling in vessels appears mainly linked to amyloid deposits, whereas apo D shows a distribution almost opposite to that of apo E. This could be an indication of the different roles that each apolipoprotein plays in the pathogenesis of amyloid deposition.

Serum amyloid a in obstructive sleep apnea

BACKGROUND

Patients with severe obstructive sleep apnea (OSA) may have increased risk for cardiovascular and cerebrovascular diseases. Serum amyloid A (SAA) protein has recently been linked to the development of atherosclerosis, stroke, diabetes, and dementia. We tested the hypothesis that plasma SAA levels are increased in otherwise healthy subjects with OSA.

METHODS AND RESULTS

Plasma SAA levels were measured in 10 male patients with moderate to severe OSA before sleep, after 5 hours of untreated OSA, and in the morning after effective continuous positive airway pressure treatment. SAA levels were also measured in 10 closely matched control subjects at similar time points. Baseline plasma SAA levels before sleep were strikingly higher in patients with moderate to severe OSA than in controls (18.8+/-2.6 versus 7.2+/-2.6 microg/mL, respectively; P=0.005) and remained unchanged in both groups throughout the night. SAA levels in 10 male patients with mild OSA were comparable with controls (P=0.46). Plasma SAA in 7 female patients with moderate to severe OSA was also markedly higher compared with matched control female subjects (24.1+/-2.4 versus 10.2+/-2.4 microg/mL, respectively; P=0.0013) but was not different from male patients with moderate to severe OSA (P=0.3). There was a significant positive correlation between SAA and apnea-hypopnea index (r=0.40, P=0.03).

CONCLUSIONS

Plasma SAA levels are more than 2-fold greater in patients with moderate to severe OSA compared with subjects with mild OSA or healthy controls regardless of gender. Elevated SAA may contribute to any increased risk for cardiovascular and neuronal dysfunction in patients with OSA.

Immunization treatment approaches in Alzheimer's and prion diseases

There is growing realization that many neurodegenerative conditions have the same underlying pathogenetic mechanism: a change in protein conformation, where the beta-sheet content is increased. In Alzheimer's disease (AD), amyloid deposition in the form of neuritic plaques and congophilic angiopathy is driven by the conversion of normal soluble amyloid beta (sAbeta) to Abeta plaques, whereas in the prionoses the critical event is the conversion of normal prion protein, PrP(C), to PrP(Sc). This common theme in the pathogenesis of these disorders and the extracellular localization of the accumulating abnormal protein make them highly amenable to therapeutic approaches based on experimental manipulation of protein conformation and clearance. Different approaches under development include drugs that affect the processing of the precursor proteins, enhance clearance of the amyloidogenic protein, and inhibit or prevent the conformation change. Particularly interesting are recent studies of immune system activation, which appear to increase the clearance of the disease-associated protein. These immunologically based approaches are highly effective in animal models of these disorders, and in these model systems are associated with no obvious side effects. In transgenic mice with AD-related pathology, immunization has also been shown to prevent age-related cognitive impairment. However, the first clinical trial of this approach in AD patients was associated with unacceptable toxicity. These immune-based treatment approaches have great potential as rational therapies for this devastating group of disorders, but additional development is needed before they can be safely applied to humans.

Only amyloidogenic intermediates of transthyretin induce apoptosis

In diseases like Alzheimer's disease and familial amyloidotic polyneuropathy (FAP) amyloid deposits co-localize with areas of neurodegeneration. FAP is associated with mutations of the plasma protein transthyretin (TTR). We can here show an apoptotic effect of amyloidogenic mutants of TTR on a human neuroblastoma cell line. Toxicity could be blocked by catalase indicating a free oxygen radical dependent mechanism. The toxic effect was dependent on the state of aggregation and unexpectedly mature fibrils from FAP-patients who failed to exert an apoptotic response. Morphological studies revealed a correlation between toxicity and the presence of immature amyloid. Thus, we can show that toxicity is associated with early stages of fibril formation and propose that mature full-length fibrils represent an inert end stage, which might serve as a rescue mechanism.

Melatonin reverses the profibrillogenic activity of apolipoprotein E4 on the Alzheimer amyloid Abeta peptide

Inheritance of apoE4 is a strong risk factor for the development of late-onset sporadic Alzheimer's disease (AD). Several lines of evidence suggest that apoE4 binds to the Alzheimer Abeta protein and, under certain experimental conditions, promotes formation of beta-sheet structures and amyloid fibrils. Deposition of amyloid fibrils is a critical step in the development of AD. We report here that addition of melatonin to Abeta in the presence of apoE resulted in a potent isoform-specific inhibition of fibril formation, the extent of which was far greater than that of the inhibition produced by melatonin alone. This effect was structure-dependent and unrelated to the antioxidant properties of melatonin, since it could be reproduced neither with the structurally related indole N-acetyl-5-hydroxytryptamine nor with the antioxidants ascorbate, alpha-tocophenol, and PBN. The enhanced inhibitory effects of melatonin and apoE were lost when bovine serum albumin was substituted for apoE. In addition, Abeta in combination with apoE was highly neurotoxic (apoE4 > apoE3) to neuronal cells in culture, and this activity was also prevented by melatonin. These findings suggest that reductions in brain melatonin, which occur during aging, may contribute to a proamyloidogenic microenvironment in the aging brain.

Neurologic erectile dysfunction

Neurologic erectile dysfunction presents a diagnostic and treatment challenge to the internist and urologist. Multiple chronic disease modalities and traumatic etiologies exist. Education regarding these conditions and a detailed and thorough history and office work-up are the best resources for the clinician. Treatment can follow the model of proceeding from the least to most invasive procedure (process of care), taking into account patient and partner satisfaction. Because the psychology of grief and loss may enter into treatment of some neurologic conditions (e.g., erectile dysfunction after radical retropubic prostatectomy, spinal cord injury, or chronic diseases), a whole-patient approach encompassing psychotherapy is warranted.

Amyloidogenesis in familial British dementia is associated with a genetic defect on chromosome 13

Familial British dementia (FBD) is a disorder characterized by the presence of amyloid deposits in cerebral blood vessels and brain parenchyma coexisting with neurofibrillary tangles in limbic areas. The amyloid subunit (ABri) is a 4 kDa fragment of a 266 amino acid type II single-spanning transmembrane precursor protein encoded by the BRI gene located on chromosome 13. In FBD patients, a single base substitution at the stop codon of this gene generates a larger 277-residue precursor (ABriPP-277). Proteolytic processing by a furin-like enzyme at the C-terminus of the elongated precursor generates the 34 amino acid ABri that undergoes rapid aggregation and fibrillization. ABri is structually unrelated to all known amyloids including A beta, the main component of the amyloid lesions in Alzheimer's disease (AD), indicating that cerebral deposition of amyloid molecules other than A beta can trigger similar neuropathological changes leading to neuronal loss and dementia. These data support the concept that amyloid deposition in the vascular wall and brain parenchyma is of primary importance in the initiation of neurogeneration.

A comparative analysis of 23 structures of the amyloidogenic protein transthyretin

Self-assembly of the human plasma protein transthyretin (TTR) into unbranched insoluble amyloid fibrils occurs as a result of point mutations that destabilize the molecule, leading to conformational changes. The tertiary structure of native soluble TTR and many of its disease-causing mutants have been determined. Several independent studies by X-ray crystallography have suggested structural differences between TTR variants which are claimed to be of significance for amyloid formation. As these changes are minor and not consistent between the studies, we have compared all TTR structures available at the protein data bank including three wild-types, three non-amyloidogenic mutants, seven amyloidogenic mutants and nine complexes. The reference for this study is a new 1.5 A resolution structure of human wild-type TTR refined to an R-factor/R-free of 18.6 %/21.6 %. The present findings are discussed in the light of the previous structural studies of TTR variants, and show the reported structural differences to be non-significant.

Apolipoprotein J (clusterin) and Alzheimer's disease

Apolipoprotein J (clusterin) is a ubiquitous multifunctional glycoprotein capable of interacting with a broad spectrum of molecules. In pathological conditions, it is an amyloid associated protein, co-localizing with fibrillar deposits in systemic and localized amyloid disorders. In Alzheimer's disease, the most frequent form of amyloidosis in humans and the major cause of dementia in the elderly, apoJ is present in amyloid plaques and cerebrovascular deposits but is rarely seen in NFT-containing neurons. ApoJ expression is up-regulated in a wide variety of insults and may represent a defense response against local damage to neurons. Four different mechanisms of action could be postulated to explain the role of apoJ as a neuroprotectant during cellular stress: (1) function as an anti-apoptotic signal, (2) protection against oxidative stress, (3) inhibition of the membrane attack complex of complement proteins locally activated as a result of inflammation, and (4) binding to hydrophobic regions of partially unfolded, stressed proteins, and therefore avoiding aggregation in a chaperone-like manner. This review focuses on the association of apoJ in biological fluids with Alzheimer's soluble Abeta. This interaction prevents Abeta aggregation and fibrillization and modulates its blood-brain barrier transport at the cerebrovascular endothelium.

Apolipoprotein E includes a binding site which is recognized by several amyloidogenic polypeptides

Inheritance of the apolipoprotein E (apoE) epsilon 4 allele is a risk factor for late-onset Alzheimer's disease (AD). Biochemically apoE is present in AD plaques and neurofibrillary tangles of the AD brain. There is a high avidity and specific binding of apoE and the amyloid beta-peptide (A beta). In addition to AD apoE is also present in many other cerebral and systemic amyloidoses, Down's syndrome and prion diseases but the pathophysiological basis for its presence is still unknown. In the present study we have compared the interaction of apoE with A beta, the gelsolin-derived amyloid fragment AGel(183-210) and the amyloidogenic prion fragments PrP(109-122) and PrP(109-141). We show that, similar to A beta, also AGel and PrP fragments can form a complex with apoE, and that the interaction between apoE and the amyloidogenic protein fragments is mediated through the same binding site on apoE. We also show that apoE increases the thioflavin-T fluorescence of PrP and AGel and that apoE influences the content of beta-sheet conformation of these amyloidogenic fragments. Our results indicate that amyloids and amyloidogenic prion fragments share a similar structural motif, which is recognized by apoE, possibly through a single binding site, and that this motif is also responsible for the amyloidogenicity of these fragments.

A newly formed amyloidogenic fragment due to a stop codon mutation causes familial British dementia

Familial British dementia (FBD) is an early-onset autosomal dominant disorder characterized by progressive cognitive impairment, spasticity, and cerebellar ataxia. Hippocampal neurofibrillar degeneration and widespread parenchymal and vascular amyloid deposits are the main neuropathological lesions. Amyloid fibrils are composed of a novel 34 amino acid subunit (ABri) with no sequence identity to any known amyloid molecule. The peptide derives from a larger precursor protein codified by a single gene BRI on chromosome 13. Affected family members have a single base substitution at the stop codon of the BRI gene that generates a longer open-reading frame resulting in a larger precursor protein. The release of the 34 C-terminal amino acids from the mutated precursor originates the ABri amyloid subunit. Our discovery of a new amyloid associated with the development of dementia supports the concept that amyloid peptides may be of primary importance in the initiation of neurodegeneration.

pH-dependent fibrillogenesis of a VkappaIII Bence Jones protein

Disorders of immunoglobulin (Ig) synthesis that occur in malignant plasma-cell proliferation may result in either granular (LCDD) or fibrillar (AL) tissue deposition of light-chain monoclonal components. The structural features that govern the transition from soluble polypeptides to either fibrillar or granular conformational states remain undefined. Among the many factors presumed to play a role in these transitions the net charge of the molecule has been associated with folding conformation changes. The majority of the proteins involved in AL amyloidosis show acidic isoelectric points (pI 3.8-5.2), whereas most L chains with basic pIs deposit in granular patterns. In our studies a 12 kD VkappaIII fragment was purified as the main component of the fibrils isolated from myocardium and adipose tissue of the pericardium obtained post-mortem from an individual with systemic AL amyloidosis. An apparently identical 12 kD VL fragment with the same N-terminal sequence constituted the BJ protein present in the urine. This urinary protein exhibited strikingly cathodic electrophoretic mobility on agarose gels and lacked retention by anionic exchange chromatography matrices, indicative of a highly basic pI (>10). When it was subjected to in vitro fibril-formation experiments, the BJ protein adopted a fibrillar conformation only at acidic pHs, remaining aggregated but not fibrillar at physiological pH. The data indicate that a specific tissue deposition pattern involves not only structural properties of the protein but rather more complex mechanisms in which acidic micro-environments may contribute to the stabilization of amyloidogenic conformations.

A stop-codon mutation in the BRI gene associated with familial British dementia

Familial British dementia (FBD), previously designated familial cerebral amyloid angiopathy-British type, is an autosomal dominant disorder of undetermined origin characterized by progressive dementia, spasticity, and cerebellar ataxia, with onset at around the fifth decade of life. Cerebral amyloid angiopathy, non-neuritic and perivascular plaques and neurofibrillary tangles are the predominant pathological lesions. Here we report the identification of a unique 4K protein subunit named ABri from isolated amyloid fibrils. This highly insoluble peptide is a fragment of a putative type-II single-spanning transmembrane precursor that is encoded by a novel gene, BRI, located on chromosome 13. A single base substitution at the stop codon of this gene generates a longer open reading frame, resulting in a larger, 277-residue precursor. Release of the 34 carboxy-terminal amino acids from the mutated precursor generates the ABri amyloid subunit. The mutation creates a cutting site for the restriction enzyme XbaI, which is useful for detecting asymptomatic carriers. Antibodies against the amyloid or homologous synthetic peptides recognize both parenchymal and vascular lesions in FBD patients. A point mutation at the stop codon of BRI therefore results in the generation of the ABri peptide, which is deposited as amyloid fibrils causing neuronal disfunction and dementia.

Transthyretin Tyr77 familial amyloid polyneuropathy: a clinicopathological study of a large kindred

More than 40 point mutations (producing different clinical manifestations) have been described in diverse points of the plasma protein transthyretin (TTR). The Met30 is considered the most common mutation, the Tyr77 mutation being the second most prevalent. However, data from patients with this late mutation are scarce, and usually come from isolated case reports or tables. The Tyr77 mutation is not as well characterized as the Met30 mutation, especially with respect to such aspects as prognosis or possible treatment by liver transplantation. We therefore present the clinical and pathological features of an extensive family with the Tyr77 TTR mutation, comprising 12 affected individuals over four generations. Six living individuals were followed over a 10-year period. Retrospective data were obtained with regard to the deceased family members. We found that an initial and sometimes prolonged carpal tunnel syndrome, beginning between the 6th and 7th decades, characterizes the Tyr77 mutation. In most cases this evolved to generalized peripheral nerve involvement, restrictive cardiomyopathy, and intestinal malabsortion. Although survival is usually high, there are progressive cases that should be candidates for liver transplant, before severe impairment has developed.

L-deprenyl: nitric oxide production and dilation of cerebral blood vessels

The monoamine oxidase-B inhibitor L-deprenyl (Selegiline) is effective in treating Parkinson's disease and possibly Alzheimer's disease. The neuroprotective property of L-deprenyl may be unrelated to the inhibition of monoamine oxidase-B. Since nitric oxide (NO) modulates activities including cerebral blood flow and memory, we examined the effect of L-deprenyl on NO. L-Deprenyl induced rapid increases in NO production in brain tissue and cerebral vessels. Vasodilation was produced by endothelial NO-dependent as well as NO-independent mechanisms in cerebral vessels. The drug also protected the vascular endothelium from the toxic effects of amyloid-beta peptide. These novel actions of selegiline may protect neurons from ischemic or oxidative damage and suggest new therapeutic applications for L-deprenyl in vascular and neurodegenerative diseases.

Cellular and molecular neurosurgery: pathways from concept to reality--part I: target disorders and concept approaches to gene therapy of the central nervous system

Recent advances in cellular and molecular biology and better understanding of genetic and biochemical bases of different central nervous system (CNS) disorders have made gene therapy of the CNS a realistic goal. Concept approaches for gene therapy of CNS disorders are reviewed and include the following: 1) gene replacement with a single normal allele to correct the inherited global neurodegenerative disorders, such as enzyme deficiencies; 2) brain repair to restore the function of a particular subset of cells that were lost because of a neurodegenerative process; 3) gene therapy of brain tumors; and 4) gene therapy of stroke. Techniques of viral vector-mediated CNS transfer of a therapeutic gene, transplantation of genetically modified cells, fetal embryonic implantation and/or implantation of genetically engineered neural progenitor cells, and production of a specific enzyme, neurotransmitter, and/or growth factor are discussed with respect to the therapeutic potential for global and localized CNS neurodegenerative disorders and stroke. Transfection of the CNS tumor cells with the drug susceptibility ("suicide") gene and/or "toxic" gene and antisense strategies and a concept of adoptive immunotherapy of brain tumors are also discussed. Other approaches, such as transfer of drug-resistant genes and monoclonal antibody gene transfer, are briefly discussed. In addition to summarizing current principles of gene therapy for several groups of CNS disorders, the issues that remain to be resolved in clinical reality, such as delivery of the genetic material and regulation of the cellular expression of the transgene, and the negatives associated with the concepts of gene therapy, such as transient gene expression, toxicity of viral proteins, drawbacks of antisense therapy, and the problem of immune response to the transfected protein, have been also identified.

Transthyretin amyloidosis: a new mutation associated with dementia

Familial transthyretin (TTR) amyloidosis commonly presents with peripheral neuropathy and involvement of visceral organs. In contrast, signs of central nervous system (CNS) involvement are exceptional. We report that members of a kindred affected by a slowly progressive dementia, seizures, ataxia, hemiparesis, and decreased vision without neuropathy have TTR amyloid deposits in the leptomeninges, the brain parenchyma, and the eye. This condition, previously labeled oculoleptomeningeal amyloidosis, is linked to a mutation at codon 30 of TTR gene, resulting in the substitution of valine with glycine in this family, TTR amyloid deposits were present in the leptomeninges, especially the leptomeningeal vessels, and in the subependymal regions of the ventricular system where they disrupted the ependymal lining and resulted in amyloid-glial formations protruding into and narrowing the ventricular system. Hydrocephalus and atrophy and infarction of cerebral and cerebellar cortexes were also present. Review of the literature shows that amyloid deposition in the leptomeninges is not uncommon in TTR amyloidoses clinically characterized by peripheral neuropathy and lack of CNS signs. The present kindred, which presented exclusively with signs of CNS involvement, expands the phenotype of TTR amyloidosis and raises questions concerning the mechanisms determining phenotypic expression in TTR familial amyloidosis.

Cerebrovascular transport of Alzheimer's amyloid beta and apolipoproteins J and E: possible anti-amyloidogenic role of the blood-brain barrier

It is uncertain whether soluble circulating amyloid beta (sA beta) is the precursor of amyloid beta (A beta) found in cerebrovascular and parenchymal amyloid lesions in Alzheimer's Disease, and if so, how the transition to the filamentous form is brought about. Several lines of evidence suggest that apolipoprotein E (apoE) and apolipoprotein J (apoJ) may be involved in the regulation of amyloidogenesis. They both bind sA beta/A beta in vivo and in vitro. It has been suggested that apoE may modulate beta-pleated conformation of A beta and therefore act as a proamyloidogenic factor. On the other hand, apoJ as a major carrier protein of sA beta in body fluids may keep the peptide in a soluble form, thus having an anti-amyloidogenic effect. Using a well established guinea-pig brain perfusion model we have studied the blood-brain barrier (BBB) processes involved in the regulation of cerebral capillary sequestration, transport and metabolism of i) sA beta 1-40 and sA beta 1-42, synthetic peptides identical to the 40 and 42 residue forms of A beta, found primarily in vascular deposits and senile plaques, respectively; and ii) apoJ, apoE3 and apoE4 alone, and in a complex with sA beta. Specific saturable BBB luminal binding of both peptides was followed by transport into brain parenchyma and metabolism at the abluminal side of the BBB and/or in brain. The capillary sequestration of sA beta 1-40 was significant, while retention by the microvasculature of sA beta 1-42 was negligible. Binding to microvessels and blood-to-brain transport of both intact apoJ and sA beta 1-40 apoJ complexes were among the highest ever recorded for peptides and proteins at the BBB in vivo. These processes appear to be mediated by glycoprotein 330 (gp330/megalin), a receptor for multiple ligands, including apoJ. In contrast, capillary retention and transport of apoE3, apoE4 and sA beta 1-40-apoE3 complex were low to negligible, while blood-brain transport of sA beta 1-40-apoE4 was moderate. It is suggested that normal BBB may have predominantly anti-amyloidogenic functions by i) degrading sA beta during blood-to-brain transport; ii) favoring sequestration and transport of apoJ alone and in complex with sA beta via gp330 receptor-mediated mechanism and iii) excluding apoE3 and apoE4 isoforms from brain.

'In vitro' amyloid fibril formation from transthyretin: the influence of ions and the amyloidogenicity of TTR variants

The mechanisms of amyloid formation in Familial Amyloidotic Polyneuropathy (FAP) are unknown, as well as the factors determining the development of this pathology. To get some insights into this process, we have first tested a fluorimetric assay with thioflavine T, as a quantitative method for transthyretin (TTR) amyloid estimation, using amyloid isolated from post-mortem tissues of a FAP patient. Then production of amyloid fibrils from soluble TTR was achieved by acidification and optimized for protein concentration and pH. The effect of different ions such as metal and sulphate ions in the process of amyloid formation from wild type TTR was compared using a kinetic assay. Under the conditions tested sulphate diminishes the amount of amyloid formed from wild type TTR and in addition appears to promote aggregation of preexisting amyloid fibrils. The relative amyloidogenicity of three TTR variants, TTR Met30, TTR Pro55 and TTR Met119 respectively, was evaluated using a pH dependent assay. It was shown that the Pro55 variant is highly susceptible to amyloid formation as compared to the wild type protein; on the contrary, the Met119 variant is more resistant than the other TTR proteins towards precipitation into amyloid. These results are in agreement with the pathological conditions associated with these mutations. This type of assay has a wide application for testing the influence of other factors, such as therapeutical agents, on amyloid formation.

Glycoprotein 330/megalin: probable role in receptor-mediated transport of apolipoprotein J alone and in a complex with Alzheimer disease amyloid beta at the blood-brain and blood-cerebrospinal fluid barriers

A soluble form of Alzheimer disease amyloid beta-protein (sA beta) is transported in the blood and cerebrospinal fluid mainly complexed with apolipoprotein J (apoJ). Using a well-characterized in situ perfused guinea pig brain model, we recently obtained preliminary evidence that apoJ facilitates transport of sA beta (1-40)-apoJ complexes across the blood-brain barrier and the blood-cerebrospinal fluid barrier, but the mechanisms remain poorly understood. In the present study, we examined the transport process in greater detail and investigated the possible role of glycoprotein 330 (gp330)/megalin, a receptor for multiple ligands, including apoJ. High-affinity transport systems with a Km of 0.2 and 0.5 nM were demonstrated for apoJ at the blood-brain barrier and the choroid epithelium in vivo, suggesting a specific receptor-mediated mechanism. The sA beta (1-40)-apoJ complex shared the same transport mechanism and exhibited 2.4- to 10.2-fold higher affinity than apoJ itself. Binding to microvessels, transport into brain parenchyma, and choroidal uptake of both apoJ and sA beta (1-40)-apoJ complexes were markedly inhibited (74-99%) in the presence of a monoclonal antibody to gp330/megalin and were virtually abolished by perfusion with the receptor-associated protein, which blocks binding of all known ligands to gp330. Western blot analysis of cerebral microvessels with the monoclonal antibody to gp330 revealed a protein with a mass identical to that in extracts of kidney membranes enriched with gp330/megalin, but in much lower concentration. The findings suggest that gp330/megalin mediates cellular uptake and transport of apoJ and sA beta (1-40)-apoJ complex at the cerebral vascular endothelium and choroid epithelium.

Blood-brain barrier uptake of the 40 and 42 amino acid sequences of circulating Alzheimer's amyloid beta in guinea pigs

An intracarotid brain infusion/capillary depletion technique was used in guinea pigs to examine cerebral capillary sequestration and transport into brain parenchyma of sA beta 1-40 and sA beta 1-42, synthetic peptides identical to two forms of the amyloid beta peptide found in Alzheimer's disease lesions: the 40 residue form, found primarily in vascular deposits, and the 42 residue form, found primarily in senile plaques. The peptides crossed well into the brain parenchyma via a specific transport mechanism for which sA beta 1-40 had an approximately two-fold greater affinity than sA beta 1-42. There was significant capillary sequestration of sA beta 1-40, but retention by the microvasculature of sA beta 1-42 was negligible. These data suggest that the level of the 40 residue peptide in cerebral vasculature and of the 42 residue peptide in parenchyma could be regulated by blood-brain barrier sequestration and transport of their respective circulating precursors.

Cerebrovascular permeability to peptides: manipulations of transport systems at the blood-brain barrier

The study of peptide transport across the blood-brain barrier (BBB) is a field fraught with conflicting interpretations. This review presents a fairly strong case that peptides can be differentially transported at the BBB. However, minimal transport of peptides could have important impact on central nervous system (CNS) functions since only small amounts are needed for physiologic pharmacologic and/or pathologic effects. Several BBB peptide transport mechanisms (i.e., receptor-mediated, absorptive-mediated, carrier-mediated and non-specific passive diffusion), as well as non-transport processes (i.e., endocytosis without transcytosis, absorption and metabolism) are discussed. It is emphasized that peptide transport systems at the BBB could be important targets for both therapeutic delivery of peptides and the development of certain brain pathologies. Strategies to manipulate peptide BBB transport processes have been discussed including lipidization, chemical modifications of the N-terminal end, coupling of transport with post-BBB metabolism and formation of potent neuroactive peptides, up-regulation of putative peptide transporters, use of chimeric peptides in which non-transportable peptide is chemically linked to a transportable peptide, use of monoclonal antibodies against peptide receptors, and binding of circulating peptides to apolipoproteins. It is suggested that future directions should be directed towards development of molecular strategies to up-regulate specific BBB peptide transporters to enhance brain delivery of peptide neuropharmaceuticals, or to down-regulate transport of peptides with potential role in cerebral pathogenesis.

Expression of human beta-amyloid peptide in transgenic Caenorhabditis elegans

Transgenic Caenorhabditis elegans nematodes have been engineered to express potentially amyloidic human proteins. These animals contain constructs in which the muscle-specific unc-54 promoter/enhancer of C. elegans drives the expression of the appropriate coding regions derived from human cDNA clones. Animals containing constructs expressing the 42-amino acid beta-amyloid peptide (derived from human amyloid precursor protein cDNA) produce muscle-specific deposits immunoreactive with anti-beta-amyloid polyclonal and monoclonal antibodies. A subset of these deposits also bind the amyloid-specific dye thioflavin S, indicating that these deposits have the tinctural characteristics of classic amyloid. Co-expression of beta-peptide and transthyretin, a protein implicated in preventing the formation of insoluble beta-amyloid, leads to a dramatic reduction in the number of dye-reactive deposits. These results suggest that this invertebrate model may be useful for in vivo investigation of factors that modulate amyloid formation.

Molecular diagnosis of transthyretin Met30 mutation in an Italian family with familial amyloidotic polyneuropathy

We report the molecular analysis of the transthyretin gene in a large Italian pedigree with familial amyloidotic polyneuropathy and demonstrate the presence of a Met30 mutation. The usefulness of the genetic analysis in the identification of presymptomatic persons and the diagnosis of individuals with partial symptoms is discussed.