Original Articles

Amyloid β Protein in Plasma as a Diagnostic Marker for Alzheimer’s Disease

Radix Salvia miltiorrhiza (RSM), a traditional Chinese medicinal herb, has been alleged to possess therapeutic effects against senile dementia, also known as Alzheimer's disease (AD). However, the effects of the major components in RSM on cytotoxicity induced by amyloid-β peptide (Aβ) and on acetylcholinesterase activity have not been studied in depth to date. In this report, the effects of RSM aqueous/ethanol extracts, total polyphenols, total tanshinones and 3 phenolic compounds against toxicity mediated by Aβ_25–35 were tested with PC-12 cells. The results showed that Aβ_25–35-induced cytotoxicity was revised by RSM aqueous/ethanol extracts and total polyphenols and that danshensu and salvianolic acid B could protect PC-12 cells by blocking Aβ_25–35-induced Ca²⁺-intake, lactate dehydrogenase release, cell viability decrease and apoptosis. In addition, the activities of RSM extracts and relevant constituents in their inhibition of acetylcholinesterase were investigated using rat brain homogenates as an enzyme resource. Galanthamine hydrobromide, an accepted acetylcholinesterase inhibitor, was employed as a positive control agent. Our preliminary studies demonstrated that RSM ethanol extract, total tanshinones, tanshinone I and dihydrotanshinone I had remarkable inhibition effects on acetylcholinesterase in vitro. These findings suggest that both tanshinones and polyphenols in RSM are the active constituents responsible for the beneficial effects of this herb in AD treatment.

The objectives of this study were to investigate the protective effects of Eucommia ulmoides Oliv. (EUO) bark and leaf against cytotoxicity induced by amyloid-β peptide (Aβ) and to explore their active components. The PC-12 cells injury mediated by Aβ_25–35 was employed to assess the neuroprotective effects of EUO bark, EUO leaf and various compounds. Intracellular Ca²⁺ determination, MTT reduction assay, lactate dehydrogenase leakage evaluation and HO33258/PI staining were used to quantitatively or qualitatively evaluate cell viability and injury. The organic solvents partition and the macroporous resin separation were also applied to tracing the active constituents of EUO bark. Moreover, the effects of 8 compounds (3 iridoid glucoside, 3 phenylpripanoids and 2 flavonoids) were tested to identify the active compounds of EUO leaf. The results demonstrated that the water extracts of EUO barks and leaves, geniposidic acid and chlorogenic acid could efficiently protect PC-12 cells against the cytotoxicity of Aβ_25–35. This research suggests that EUO may represent a potential treatment strategy for Alzheimer's disease. Meanwhile, geniposidic acid and chlorogenic acid are the major active constituents of EUO barks and leaves, respectively.

With the emergence of a promising approach to treat Alzheimer disease (AD) targeting the β-amyloid (Aβ) pathway, it is necessary to establish new diagnostic biomarkers that enable the antemortem diagnosis of AD. Although plasma Aβ has been suggested as a non-invasive biomarker, its significance has been inconclusive. Thus, it is important to improve the diagnostic potential of plasma Aβ. One of the potential approaches is to modify plasma Aβ level using various modulators. In this study, we evaluated the influence of glucometabolic status on plasma Aβ level in two lines of AD transgenic mouse. The present study demonstrated that plasma Aβ level rapidly increased after glucose loading. More importantly, the magnitude of the increase in plasma Aβ was significantly larger in AD transgenic mice than in wild-type littermates. These findings might provide a novel diagnostic tool for AD using the elevation of plasma Aβ level after glucose loading.

Amyloid β peptides (Aβ) are important components of plaques in Alzheimer's disease. Plasma concentrations of Aβ_1–40 and Aβ_1–42 rise with age and are increased in people with mutations that cause early-onset Alzheimer's disease. However, Aβ_1–42 concentrations may decrease early in the dementia process. We postulated that concentrations of Aβ_1–40 and Aβ_1–42 in plasma are associated with risk of dementia.

We did a case-cohort study embedded in the prospective, population-based Rotterdam Study. Of 6713 participants at risk for dementia, a random sample of 1756 people was drawn. During follow-up (mean 8·6 years), 392 incident dementia cases were identified. We investigated the association between plasma Aβ concentrations and risk of dementia and its subtypes using Cox proportional hazard models.

High concentrations of Aβ_1–40 but not Aβ_1–42 at baseline were associated with an increased risk of dementia. Compared with the first quartile of Aβ_1–40, age and sex-adjusted hazard ratios for dementia for the second, third, and fourth quartiles were 1·07 (95% CI 0·72–1·58), 1·16 (0·78–1·70), and 1·46 (1·01–2·12). People with an increased Aβ_1–42/Aβ_1–40 ratio had a reduced risk of dementia. Compared with the first quartile of the Aβ_1–42/Aβ_1–40 ratio, hazard ratios for the second, third, and fourth quartiles were 0·74 (0·53–1·02), 0·62 (0·44–0·88), and 0·47 (0·33–0·67). Associations were similar for Alzheimer's disease and vascular dementia.

High plasma concentrations of Aβ_1–40, especially when combined with low concentrations of Aβ_1–42, indicate an increased risk of dementia. A potential role of plasma Aβ concentrations as a marker of incipient dementia warrants further investigation.

Accumulation of Aβ protein in β-amyloid deposits is a hallmark event in Alzheimer's disease (AD). Recent findings suggest anti-Aβ autoantibodies may have a role in AD pathology. However, a consensus has yet to emerge as to whether endogenous anti-Aβ autoantibodies are elevated, depressed, or unchanged in AD patients. Whereas experiments to date have used synthetic unmodified monomeric Aβ (Aβ_mon) to test autoimmunity, up to 40% of the Aβ pool inB AD brain consists of low molecular weight oligomeric cross-linked β-amyloid protein species (CAPS). Recent studies also suggest that CAPS may be the primary neurotoxic agent in AD. In the present study, AD and nondemented control plasma were analyzed for immunoreactivity to CAPS and Aβ_mon. Plasma of both nondemented and AD patients were found to contain autoantibodies specific for soluble CAPS. Nondemented control and AD plasmas demonstrated similar immunoreactivity to Aβ_mon. In contrast, anti-CAPS antibodies in AD plasma were found to be significantly reduced compared with nondemented controls (p = 0.018). Furthermore, age at onset for AD correlated significantly (p = 0.041) with plasma immunoreactivity to CAPS. These data suggest that autoantibodies to CAPS are depleted in AD patients and raise the prospect that immunization with anti-CAPS antibodies might provide therapeutic benefit for AD.