Proteolysis of Alzheimer's disease beta-amyloid precursor protein by factor Xa

Coagulation factor XIII Val34Leu gene polymorphism and Alzheimer's disease

Blood coagulation factor XIII (FXIII) plays a role in inflammatory processes and a pathogenetic role of inflammation in neurodegenerative disorders has been proposed. FXIIIa subunit was immunohistochemically detected in a subpopulation of reactive microglia in Alzheimer's disease (AD). Aim of the present study is to evaluate whether a common polymorphism of the FXIII gene is associated with sporadic AD. We examined 90 patients affected by sporadic AD and 139 age- and sex-matched controls to assess the distribution of V/L alleles and genotypes of the FXIIIa-subunit gene. The LL genotype showed a significantly higher frequency in AD patients (p<0.05) with a significantly increased risk of AD in the presence of LL genotype at the logistic regression analysis [odds ratio: 3.6 (1.36-9.44), p<0.01]. This study shows for the first time an association between FXIII Val34Leu polymorphism and AD.

Pharmacodynamics and pharmacokinetics of C3, a heparin-derived oligosaccharide mixture, in non-human primates

The heparin-derived oligosaccharide C3 (C3) is currently underdevelopment for the prevention and treatment of vascular dementia and senile dementia of Alzheimer's type. C3 exhibits a molecular weight of 2200-2500 Da with a narrow distribution. The objective of the present study was to assess the pharmacodynamics and pharmacokinetics of C3 in non-human primates. C3 was administered as an intravenous or subcutaneous bolus dose of 1.0 or 2.5 mg/kg. Anti-factor Xa activity, Heptest clotting time and activated partial thromboplastin time were measured to determine pharmacodynamic effects of C3 in plasma. The pharmacokinetics of C3 was primarily characterized by measuring plasma anti-factor Xa activity as a surrogate marker. The rate of absorption and elimination of C3 after administration did not change with increasing dose. The volume of distribution of C3 was small, reflecting a major distribution inside the intravascular space (110-130 ml/kg), and was independent of dose. The total clearance (16.0-21.0 ml/h/kg) and half-life (4-6 h) of C3 were also dose-independent. Within the observed dose range, a 2.5 times of the C3 dose resulted in an area under the plasma concentration-time curve that was approximately 16-27% greater than expected on the basis of linear disposition. These differences could be attributed to the endogenous release of tissue factor pathway inhibitor (TFPI) by C3 at higher doses, which is associated with the vascular effects of C3.

Advances in the cellular and molecular biology of the beta-amyloid protein in Alzheimer's disease

Alzheimer's disease (AD) is a progressive senile dementia characterized by deposition of a 4 kDa peptide of 39-42 residues known as amyloid beta-peptide (Abeta) in the form of senile plaques and the microtubule associated protein tau as paired helical filaments. Genetic studies have identified mutations in the Abeta precursor protein (APP) as the key triggers for the pathogenesis of AD. Other genes such as presenilins 1 and 2 (PS1/2) and apolipoprotein E (APOE) also play a critical role in increased Abeta deposition. Several biochemical and molecular studies using transfected cells and transgenic animals point to mechanisms by which Abeta is generated and aggregated to trigger the neurodegeneration that may cause AD. Three important enzymes collectively known as "secretases" participate in APP processing. An enzymatic activity, beta-secretase, cleaves APP on the amino side of Abeta producing a large secreted derivative, sAPPbeta, and an Abeta-bearing membrane-associated C-terminal derivative, CTFbeta, which is subsequently cleaved by the second activity, gamma-secretase, to release Abeta. Alternatively, a third activity, alpha-secretase, cleaves APP within Abeta to the secreted derivative sAPPalpha and membrane-associated CTFalpha. The predominant secreted APP derivative is sAPPalpha in most cell-types. Most of the secreted Abeta is 40 residues long (Abeta40) although a small percentage is 42 residues in length (Abeta42). However, the longer Abeta42 aggregates more readily and was therefore considered to be the pathologically important form. Advances in our understanding of APP processing, trafficking, and turnover will pave the way for better drug discovery for the eventual treatment of AD. In addition, APP gene regulation and its interaction with other proteins may provide useful drug targets for AD. The emerging knowledge related to the normal function of APP will help in determining whether or not the AD associated changes in APP metabolism affect its function. The present review summarizes our current understanding of APP metabolism and function and their relationship to other proteins involved in AD.

Localization of a novel type trypsin-like serine protease, neurosin, in brain tissues of Alzheimer's disease and Parkinson's disease

Neurosin, a novel type of trypsin-like serine protease, has been shown to be preferentially expressed in human brain by northern blotting. We examined neurosin immunolabeling in the brains of neurologically normal persons and patients with Alzheimer's disease (AD) and with Parkinson's disease. We also identified the expression of the mRNA for neurosin by in situ hybridization histochemistry and reverse transcription-polymerase chain reaction (RT-PCR). The neurosin antibody stained all of the nuclei of various cell types. In neurons, there was also staining of neuronal cytoplasm, nucleoli and their processes. In AD, staining of neurons with processes was rare in the damaged areas. Some senile plaques, extracellular tangles and Lewy bodies were also positive for neurosin. Expression of the mRNA for neurosin was seen in neurons in the gray matter, and in microglial cells in the white matter. In AD, the intensity of the signal for neurosin mRNA in the gray matter was decreased compared with normal control brains. The relative levels of neurosin mRNA in AD brains, measured by RT-PCR, were lower than those in controls. These results suggest that in human brain neurosin plays various physiological roles, and that in AD this molecule, like other serine proteases, may have a role in the degradation of such substances as beta-amyloid protein.

Prothrombin concentration in the cerebrospinal fluid is not altered in Alzheimer's disease

Prothrombin, known to be expressed in brain and to possess growth modulating properties, has been suggested to be involved in the pathogenesis of Alzheimer's disease (AD). We studied prothrombin concentration in lumbar CSF (L-CSF) in patients with AD (n = 25), neurologic disease controls (NDC; n = 33) covering a wide range of neurologic disorders, and subjects with Guillain-Barre syndrome (GBS; n = 4) as well as in samples of non-pathological ventricular CSF (V-CSF; n = 4). The results were evaluated with respect to CSF flow rate, as indicated by the albumin quotient (Q(Alb)). The concentrations of prothrombin in L-CSF in NDC (mean: 0.46 mg/l, range: 0.21-0.96), and AD (mean: 0.6 mg/l, range: 0.19-1.2) were in the normal range reported previously. Expectedly, prothrombin concentration in L-CSF of GBS was increased (mean: 6.3 mg/l, range: 2.3-9.7) corresponding to the increased Q(Alb) in this group (mean 54.6x10(-3), range: 17-88.1). The concentrations of both prothrombin and albumin were 5.5-fold higher in L-CSF than in V-CSF (mean Q(Alb) : 1.1x10(-3), mean concentration of prothrombin: 0.088 mg/l). In conclusion, CSF prothrombin in all conditions evaluated here is exclusively derived from blood.

The amyloid beta-protein precursor of Alzheimer's disease is degraded extracellularly by a Kunitz protease inhibitor domain-sensitive trypsin-like serine protease in cultures of chick sympathetic neurons

The amyloid beta-protein precursor (APP) of Alzheimer's disease (AD) is cleaved either by alpha-secretase to generate an N-terminally secreted fragment, or by beta- and gamma-secretases to generate the beta-amyloid protein (Abeta). The accumulation of Abeta in the brain is an important step in the pathogenesis of AD. Alternative mRNA splicing can generate isoforms of APP which contain a Kunitz protease inhibitor (KPI) domain. However, little is known about the physiological function of this domain. In the present study, the metabolic turnover of APP was examined in cultured chick sympathetic neurons. APP was labelled by incubating neurons for 5 h with [35S]methionine and [35S]cysteine. Intracellular labelled APP decayed in a biphasic pattern suggesting that trafficking occurs through two metabolic compartments. The half-lives for APP in each compartment were 1.5 and 5.7 h, respectively. A small fraction (10%) of the total APP was secreted into the culture medium where it was degraded with a half-life of 9 h. Studies using specific protease inhibitors demonstrated that this extracellular breakdown was due to cleavage by a trypsin-like serine protease that was secreted into the culture medium. Significantly, this protease was inhibited by a recombinant isoform of APP (sAPP751), which contains a region homologous to the Kunitz protease inhibitor (KPI) domain. These results suggest that KPI forms of APP regulate extracellular cleavage of secreted APP by inhibiting the activity of a secreted APP-degrading protease.