Reactive astrocytes and alpha1-antichymotrypsin in Alzheimer's disease.

There is ample genetic, biochemical, cellular and molecular evidence to show that the amyloid beta peptide (Abeta), a proteolytic fragment of the amyloid precursor protein (APP), plays an important, if not causative role in Alzheimer's disease (AD). An additional hallmark of AD is the neuroinflammatory response that is associated with the amyloid deposition. We discovered that the acute phase protein alpha1-antichymotrypsin (ACT) is overexpressed by reactive astrocytes, and is tightly associated with virtually all amyloid plaques in the AD brain. It has also been shown that Abeta and ACT bind in vitro. Recently, we have reported that astrocytic expression of ACT in APP transgenic mice leads to an increased plaque deposition in ACT/APP doubly transgenic mice compared to the APP mice alone, suggesting that ACT interferes with Abeta clearance. The main objective of this review is to summarize the role of astrocytosis and ACT in the pathogenesis of AD.     

Familial alpha 1-antichymotrypsin deficiency

We studied patients and their relatives with partial deficiency, approximately 50% of normal plasma levels, of alpha 1-antichymotrypsin (ACT), an acute phase reactant with anti-cathepsin G activity. Six of eight ACT deficient individuals, over 25 years of age, had liver and three of eight lung manifestations, varying from severe disease to subtle laboratory abnormalities. The ACT of deficient individuals (who are heterozygotes for a rare gene, q = 0.003) had normal crossed immunoelectrophoretic properties. The abnormal gene is inherited in an autosomal, dominant way. The results suggest that deficiency of this antiprotease, which also has immune response modulating properties, may predispose to liver and lung disease.     

Plasma alpha1-antichymotrypsin in Alzheimer's disease; relationships with APOE genotypes

Inflammatory processes are thought to be important contributors to the pathogenesis of Alzheimer's disease (AD). alpha1-antichymotrypsin (ACT) is a proteinase inhibitor characteristic of acute-phase inflammation and has been identified in amyloid plaques. We analyzed the plasma ACT levels in a sample of subjects with late-onset AD and correspondent controls. Plasma ACT was higher in AD patients (62.8 +/- 20.2 mg/dl) than in controls (58.8 +/- 18.1 mg/dl), but not significantly (P = 0.13). In the AD patients regression analysis showed a positive linear relationship between ACT levels and duration of the disease (P = 0.037). Increased ACT concentrations (64.6 +/- 21.2 mg/dl) were also found in patients with greater cognitive impairment (MMSE scores < 20), but since this factor depends on the duration of the disease as well, our present data seem to indicate a complex relationship involving elevated ACT levels, disease duration and cognitive impairment. Plasma ACT was found to differ significantly according to APOE genotypes (P = 0.017), the highest levels being associated to E3-E3 homozygotes (66.1 +/- 17.8 mg/dl) and the lowest to E4-E3 subjects (53.1 +/- 18.2 mg/dl). In patients not carrying APOE*4 allele the ACT levels were higher than in controls (P = 0.014), and the relationship between ACT and disease duration was stronger than that observed in the total AD sample (P = 0.003), but it was absent in those carrying APOE*4 (P = 0.67). Taken together our results seem to suggest that inflammation is a relevant factor in AD pathogenesis for subjects with E3-E3 and E3-E2 genotypes but less important for APOE*4 carrying subjects.     

Genetic association study between alpha 1-antichymotrypsin polymorphism and Alzheimer disease in Chinese Han population

We investigated a common signal peptide polymorphism in the alpha 1-antichymotrypsin (ACT) gene in 125 sporadic Alzheimer disease (AD) patients and 141 healthy control subjects in Chinese Han population. We found no significant difference in the distribution of ACT polymorphism between AD cases and controls, and failed to detect any effects of ACT genotypes associated with AD. Thus, our data do not support the involvement of ACT polymorphism in the risk of AD in Chinese Han population. Am. J. Med. Genet. (Neuropsychiatr. Genet.) 96:133-135, 2000.     

Alpha 1-antichymotrypsin is present in diffuse senile plaques. A comparative study of beta-protein and alpha 1-antichymotrypsin immunostaining in the Alzheimer brain.

Immunocytochemical examinations of the brains of patients with senile dementia of the Alzheimer type, Down''s syndrome, and Gerstmann-Sträusslar-Scheinker disease were performed to clarify the relationship between alpha 1-antichymotrypsin and senile plaque amyloids. Alpha 1-antichymotrypsinlike immunoreactivity was enhanced by protease digestion but not by formic acid pretreatment. Almost all of the diffuse plaques and some small amyloid deposits, which were widely distributed in the cerebral cortex and/or subcortical regions of SDAT brains, were labeled by alpha 1-antichymotrypsin immunostaining. All types of senile plaques, eosinophilic tangles, and some neurons and astrocytes were labeled by alpha 1-antichymotrypsin staining. Diffuse plaques in a Down''s syndrome frontal lobe and in a senile dementia of the Alzheimer type cerebellum also were labeled by alpha 1-antichymotrypsin immunostaining. However neither subpial amyloid deposits nor subcortical small amyloid deposits could be detected by alpha 1-antichymotrypsin immunostaining. Kuru plaques in a Gerstmann-Sträusslar-Scheinker disease cerebellum also were not labeled by alpha 1-antichymotrypsin immunostaining. These results suggest that alpha 1-antichymotrypsin is associated with the early to late stages of amyloid deposition and senile plaque formation in senile demential of the Alzheimer type.     

Alpha 1-antichymotrypsin is associated solely with amyloid deposits containing the beta-protein. Amyloid and cell localization of alpha 1-antichymotrypsin

Our recent studies demonstrated that alpha 1-antichymotrypsin (ACT), a serine protease inhibitor, was associated with the beta-protein in the brain amyloid deposits of Alzheimer's disease, aged human controls and aged monkeys, suggesting a role for the inhibitor in the amyloid deposition. In the present study we used immunohistochemistry to test for the presence of ACT in the amyloid deposits which contain, as their major component, a protein different from the beta-protein. ACT was not found in the amyloid deposits in primary or secondary amyloidosis, familial and amyloidotic polyneuropathy or Creutzfeldt-Jakob disease (non-beta-protein amyloidoses), but was found (together with beta-protein) in Alzheimer's disease, Down's syndrome, normal aging, and hereditary cerebral hemorrhage with amyloidosis of Dutch origin. These results suggest a specific association of ACT with beta-protein amyloid. We next examined the distribution of the inhibitor in normal human brain and in various human neuropathological states in order to identify cells that express this protein during brain degeneration. In addition to its association with amyloid, ACT immunoreactivity was also located in astrocytes near areas of neuronal or tissue loss, in a few neurons and pericytes and in the epithelium of the choroid plexus.     

Study of alpha1-antichymotrypsin (ACT) in prostatic carcinoma

10 normal prostates and 100 prostates with tumour were studied immunohistochemically. ACT was found mainly in the cells lining the ducts. Synthesis of ACT is significantly increased in carcinoma due to mainly two parallel processes: ACT production by carcinoma cells and intensification of its production by normal cells mainly at the tumour periphery. Hyperplastic structures showed not very high ACT content, adenomatous structures revealed a higher response. On the whole, there is a parallelism between the content of ACT and prostatic specific antigen (PSA) in both normal and carcinomatous prostate, however PSA is being found in a much more wider spectrum of cells. Content of ACT in seminal fluid may be used as a parameter for diagnosis and monitoring of prostate cancer.     

Moraxella-dependent alpha 1-antichymotrypsin neutralization: a unique virulence mechanism

The acute phase reactant and protease inhibitor alpha(1)-antichymotrypsin is considered to play a protective role in the airways, but whether it interacts with respiratory bacteria is not known. We analyzed whether the common respiratory pathogens Streptococcus pneumoniae, Haemophilus influenzae, Moraxella catarrhalis, and other bacterial species interact with antichymotrypsin. M. catarrhalis was the only species that bound antichymotrypsin among 25 bacterial species tested by flow cytometry and direct binding assay. We compared a series of clinical isolates in addition to wild-type and ubiquitous surface protein-deficient Moraxella to study the nature of antichymotrypsin binding by the bacteria. Experiments with Moraxella mutants revealed that ubiquitous surface proteins A1 and A2 were responsible for the interaction, and using recombinant fragments, a consensus sequence within ubiquitous surface proteins A1 and A2 was defined. Binding of iodine-labeled antichymotrypsin was dose dependent and strong (dissociation constant [K(d)] 24.9-44.8 nM). Moreover, a chymotrypsin activity assay showed that antichymotrypsin, when bound to the bacterial surface, was neutralized. Moraxella antichymotrypsin neutralization is a novel microbial virulence mechanism that may induce excessive inflammation resulting in more exposed extracellular matrix that is beneficial for bacterial colonization.     

Distribution of plasma alpha 1-antichymotrypsin levels in Alzheimer disease patients and controls and their genetic controls

Alzheimer's disease (AD) is a complex multifactorial disease in which many genetic and environmental factors are involved. Recent studies have shown that alpha(1)-antichymotrypsin (ACT) is one of the candidate genes for AD. Elevated levels of ACT have been widely, but not universally reported in the cerebrospinal fluid and plasma of AD patients. The genetic association between the ACT/codon -17*A allele of the signal peptide polymorphism and AD has been shown in some studies. One hypothesis is that the ACT/codon -17*A allele is in linkage disequilibrium with unknown functional mutation(s) in the ACT gene. Alternatively, the more hydrophobic character of the alanine (codon -17*A) may enhance ACT translocation into the endoplasmic reticulum and the Golgi apparatus, thus being secreted at higher levels. Therefore, this study was undertaken to determine the distribution of ACT plasma levels in cases (n = 397) and controls (n = 118) and the impact of ACT polymorphisms, including codon -17, on plasma ACT levels. In our cohort, plasma ACT levels were significantly higher in AD patients than controls (542.13 +/- 7.11 mg/liter vs. 496.62 +/- 12.79 mg/liter; P = 0.002). The ACT/codon -17 polymorphism showed significant association with ACT levels in male AD patients, while the effect of the intron 4 polymorphism was significant in both male and female patients. Codon 227 polymorphism was associated with lower ACT levels in AD patients. In conclusion, ACT may play an important role in the AD pathogenesis and genetic variation in the ACT gene appears to have some effect on plasma ACT concentrations.     

The role of the acute-phase protein alpha 1-antichymotrypsin in brain dysfunction and injury.

The crystal structure of proteolytically modified human ACT has been solved at 2.7-A resolution (Baumann et al., 1991). The final model consists of 374 amino acids, 126 solvent molecules and 5 sugar residues. Asn70 is glycosylated and Asn104 is probably glycosylated. The role of carbohydrates in serpin function may be 3-fold: secretion, removal from circulation and recognition by receptors for complex uptake (Travis et al., 1990). Experiments with recombinant, non-glycosylated ACT have shown that glycosylation has no effect on the association rates of ACT with its target proteases (Rubin et al., 1990). The X-ray diffraction studies also revealed that a certain ACT region is involved in DNA binding, although the physiologic relevance of this binding is still unknown. Using a plethora of techniques, scientists are starting to understand the role of ACT in health and disease. It is 14 years since ACT was first purified (Travis et al., 1978) and 9 years since its gene was cloned (Chandra et al., 1983). We have learned considerably about this protease inhibitor in humans and rodents; in inflammation, cancer and AD; as binding to proteases (irreversibly), to the A beta (irreversibly) and to DNA. However, there are still open avenues for research. These include: finding the proteases that ACT inhibits in brain, identifying the cellular receptors which bind ACT-protease complexes and elucidating the DNA-binding phenomenon. Recently, 4 mutations have been found in APP. The first mutation at position 22 of A beta was detected in HCHWA-D by Levy et al. (1991).(ABSTRACT TRUNCATED AT 250 WORDS)     

Immunohistochemical demonstration of alpha1-antichymotrypsin and alpha1 -antitrypsin in the normal pituitary gland and its tumors

The immunohistochemical distribution of the protease inhibitors alpha₁-antichymotrypsin (alpha₁-ACT) and alpha₁-antitrypsin (alpha₁-AT) has been documented in the normal human pituitary gland and in a series of pituitary tumors. In normal gland, alpha₁-ACT was localized mainly in the dendritic folliculostellate cells, identified by immunopositivity for S 100 protein. A minority of endocrine cells also stained in 3 of 10 autopsy glands. Folliculostellate cells were identified in 11 of 28 tumors, and again, the distribution of alpha₁-ACT positivity corresponded to these cells. In 4 cases, there was staining of a small minority of tumor cells. Alpha₁-AT was localized to colloid in the microfollicles of the anterior lobe. In I normal gland, there was granular staining of endocrine cells. Alpha₁-AT was present in 5 tumors, in microfollicles and in scattered endocrine cells in 2 adenomas. These data would support a physiological role for alpha₁-ACT and alpha₁-AT in the pituitary gland. Their differing distribution might reflect different functions.     

Immunohistochemical localization of lysozyme, lactoferrin, alpha 1-antichymotrypsin, and alpha 1-antitrypsin in salivary gland of human fetuses.

26 human fetuses were examined to elucidate the immunohistochemical distributions of lysozyme, lactoferrin, alpha 1-antichymotrypsin, and alpha 1-antitrypsin in prenatal salivary glands. Development of fetal salivary glands was divided into 4 stages: The early developmental stage (EDS), the early intermediate developmental stage (EIDS), the late intermediate developmental stage (LIDS), and the late developmental stage (LDS) and were used to compare antigen localization during salivary gland development. Lysozyme (LY) staining was prominent in serous or demilune cells of the mucous acinar compartment. Lactoferrin (LF) was rarely seen in the fetal glands; only trace amounts were seen in serous cells, alpha 1-antichymotrypsin (alpha 1-ACT) was diffusely positive particularly in glandular ducts, alpha 1-antitrypsin (alpha 1-AT) was also diffusely distributed in all salivary gland elements and was more abundant in ductal cells than acinar cells. During the EDS, immunohistochemical staining of LY, LF, alpha 1-ACT, and alpha 1-AT could be observed with glandular intensity increases corresponding to the advance of cytodifferentiation of granular epithelium occurring in the subsequent EIDS and LIDS. Staining intensities were continuous during the LDS even though the amount of those materials in the fetal salivary glands was not of the extent seen in the adult salivary gland. These results suggest that production of LY, LF, alpha 1-ACT, and alpha 1-AT was positive during prenatal development of human salivary glands. The present study discusses the protective roles and defense mechanisms of LY, LF, alpha 1-ACT, and alpha 1-AT in developing human salivary glands.     

Unbiased whole-brain analysis of gray matter loss in Alzheimer's disease

In patients with Alzheimer's disease, substantial tissue loss occurs in the medial temporal lobe. In this study, we applied a voxel-based, unbiased whole-brain analysis method to compare magnetic resonance imaging scans of seven patients with Alzheimer's disease and seven healthy elderly controls. Images were transformed to standard coordinate space and tested for gray matter loss in patients. We found symmetrical decreases of gray matter in patients in the hippocampus, and, unexpectedly, also in the head of the caudate nucleus and the insula. The exact role of these two structures in the symptomatology of Alzheimer's disease deserves further attention.     

Genetic risk factors in Alzheimer''s disease.

Following a brief introduction and discussion of the pathological features of Alzheimer's disease, the main emphasis of this review article will be the genetic factors that have been implicated in this disease. These can be divided into two main categories. First, the three genes in which mutations are known to result in early onset autosomal dominant familial Alzheimer's disease will be discussed. These are well characterised but account for only a small proportion of Alzheimer's disease cases. Late onset, sporadic Alzheimer's disease is more common and evidence suggests that there is a genetic component to this type of disease. A number of genetic risk factors have been implicated that might increase the risk of developing sporadic disease. Many of these are controversial and studies have shown conflicting results, which are discussed in this section. Finally, a brief discussion of some of the mechanisms suggested to play a role in the pathogenesis of Alzheimer's disease is included. It is hoped that this will show why particular genes have been implicated in Alzheimer's disease and how they might be able to influence the development of the disease.