Reduced platelet amyloid precursor protein ratio (APP ratio) predicts conversion from mild cognitive impairment to Alzheimer's disease.

Studies have shown that platelet APP ratio (representing the percentage of 120-130 kDa to 110 kDa isoforms of the amyloid precursor protein) is reduced in patients with mild cognitive impairment (MCI) and Alzheimer's disease (AD). In the present study, we sought to determine if baseline APP ratio predicts the conversion from MCI to AD dementia after 4 years of longitudinal assessment. Fifty-five older adults with varying degrees of cognitive impairment (34 with MCI and 21 with AD) were assessed at baseline and after 4 years. MCI patients were re-classified according to the conversion status upon follow-up: 25 individuals retained the diagnostic status of MCI and were considered as stable cases (MCI-MCI); conversely, in nine cases the diagnosis of dementia due to AD was ascertained. The APP ratio (APPr) was determined by the Western blot method in samples of platelets collected at baseline. We found a significant reduction of APPr in MCI patients who converted to dementia upon follow-up. These individuals had baseline APPr values similar to those of demented AD patients. The overall accuracy of APPr to identify subjects with MCI who will progress to AD was 0.74 ± 0.10, p = 0.05. The cut-off of 1.12 yielded a sensitivity of 75 % and a specificity of 75 %. Platelet APPr may be a surrogate marker of the disease process in AD, with potential implications for the assessment of abnormalities in the APP metabolism in patients with and at risk for dementia. However, diagnostic accuracy was relatively low. Therefore, studies in larger samples are needed to determine whether APPr may warrant its use as a biomarker to support the early diagnosis of AD.

A radioenzymatic assay to identify three groups of phospholipase A(2) in platelets.

Phospholipases A(2) (PLA(2)) are key enzymes in membrane metabolism. The release of fatty acids and lysophospholipids by PLA(2) activates several intra-cellular second messenger cascades that regulate a wide variety of physiological responses. The aim of the present study is to describe a radioenzymatic assay to determine the activity of three main PLA(2) subtypes in platelets, namely extracellular calcium-dependent PLA(2) (sPLA(2)) and intracellular calcium-dependent (cPLA(2)) and calcium-independent PLA(2) (iPLA(2)). The differentiation of these distinct PLA(2) subtypes was based on the enzyme substrate preference (arachdonic acid or palmitoyl acid) and calcium concentration. Our results indicate that this new assay is feasible, precise and specific to measure the activity of the aforementioned subtypes of PLA(2). Therefore, this protocol can be used to investigate modifications of PLA(2) homeostasis in distinct biological models addressing the pathophysiology of many medical and neuropsychiatric disorders such as schizophrenia and Alzheimer's disease.

Abnormal APP processing in platelets of patients with Alzheimer's disease: correlations with membrane fluidity and cognitive decline.

RATIONALE: Previous studies have implicated platelet amyloid precursor protein (APP) as a candidate biomarker for Alzheimer's disease (AD). Platelets contain more than 95% of the circulating APP and enclose the enzymatic machinery for the APP metabolism yielding both soluble APP and amyloid-beta peptides. OBJECTIVES: The objective of this study is to compare the ratio of 130- to 110-kDa fragments of APP in platelets from patients with AD, mild cognitive impairment (MCI), and elderly controls. MATERIALS AND METHODS: After subjects were grouped according to diagnosis, APP ratio in platelets was evaluated by means of Western blot analysis. RESULTS: The APP ratio was significantly lower in AD patients (1.01 +/- 0.21) as compared to controls (1.24 +/- 0.21, p = 0.001) and MCI patients (1.18 +/- 0.21, p = 0.027), but no significant differences were found between MCI and controls (p = 0.904). In addition, we found positive correlations between the APP ratio and 1,6-diphenyl-1,3,5-hexatriene anisotropy (r = 0.3, p = 0.01), as well as with certain parameters of cognitive decline, namely, the mini-mental state examination score (r = 0.33, p = 0.003), the total Cambridge cognitive test (CAMCOG) score (r = 0.37, p = 0.001), and the score on the memory subscale of the CAMCOG (r = 0.38, p = 0.001). CONCLUSIONS: The pattern of platelet APP fragments was altered in patients with AD but not in patients with MCI. The alteration of APP fragments was correlated with membrane fluidity and the cognitive decline.

Determination of paroxetine in geriatric depression by high-performance liquid chromatography.

An HPLC method was developed for the determination of paroxetine in depressed geriatric patients. This method includes only one-step extraction of paroxetine from 1 ml of plasma with hexane:isoamyl alcohol (99:1, v/v). Separation was obtained using an RP select B column (250 mm x 4 mm, 5 microm) under isocratic conditions with UV detection (lambda=205 nm). The mobile phase was 0.05 mol/l sodium phosphate buffer, pH 5.0, and acetonitrile (50:50, v/v). The intra- and inter-assay accuracy and precision, determined as relative error and relative standard deviation, respectively, were less than 10%. The lower limit of quantification, with relative error and relative standard deviation of less than 10%, was 5 ng/ml. Linearity was assessed in the 5-1250 ng/ml range and recovery was 80%. Neither endogenous compounds nor other drugs were found to interfere. The assay showed high specificity, even when patients were found to be on multiple medications. In conclusion, the present method, when compared to others reported in the literature, has advantages such as simplicity, selectivity and sensitivity as a routine procedure and can be applied to the therapeutic monitoring of depressed geriatric patients.