Effects of processing and storage conditions on amyloid beta (1-42) and tau concentrations in cerebrospinal fluid: implications for use in clinical practice.

BACKGROUND: Reported concentrations of amyloid beta (1-42) (A beta 42) and tau in cerebrospinal fluid (CSF) differ among reports. We investigated the effects of storage temperature, repeated freeze/thaw cycles, and centrifugation on the concentrations of A beta 42 and tau in CSF. METHODS: Stability of samples stored at -80 degrees C was determined by use of an accelerated stability testing protocol according to the Arrhenius equation. A beta 42 and tau concentrations were measured in CSF samples stored at 4, 18, 37, and -80 degrees C. Relative CSF concentrations (%) of the biomarkers after one freeze/thaw cycle were compared with those after two, three, four, five, and six freeze/thaw cycles. In addition, relative A beta 42 and tau concentrations in samples not centrifuged were compared with samples centrifuged after 1, 4, 48, and 72 h. RESULTS: A beta 42 and tau concentrations were stable in CSF when stored for a long period at -80 degrees C. CSF A beta 42 decreased by 20% during the first 2 days at 4, 18, and 37 degrees C compared with -80 degrees C. CSF tau decreased after storage for 12 days at 37 degrees C. After three freeze/thaw cycles, CSF A beta 42 decreased 20%. CSF tau was stable during six freeze/thaw cycles. Centrifugation did not influence the biomarker concentrations. CONCLUSIONS: Repeated freeze/thaw cycles and storage at 4, 18, and 37 degrees C influence the quantitative result of the A beta 42 test. Preferably, samples should be stored at -80 degrees C immediately after collection.

The role of cyclo-oxygenase 1 and 2 activity in prostaglandin E(2) secretion by cultured human adult microglia: implications for Alzheimer's disease.

Microglial cyclo-oxygenase (COX) expression is considered to be important in the pathogenesis of Alzheimer's disease (AD) and, therefore, constitutes a key target for therapeutic intervention. We investigated the influence of AD plaque associated factors on COX-1 and COX-2 expression and activity in adult human microglial cells in vitro. COX-2 immunoreactivity and mRNA were induced by lipopolysaccharide (LPS), not by AD plaque associated cytokines interleukin (IL)-1alpha, IL-1beta, IL-6, tumor necrosis factor (TNF)-alpha, or amyloid (A)beta(1-42). To assess functional COX activity, the release of PGE(2) into the culture medium was determined. LPS and also arachidonic acid (AA) dose-dependently stimulated PGE(2) release. The effects of AA are independent from induction of COX mRNA expression, or of de novo protein synthesis. No effects of either plaque-associated cytokines or Abeta(1-42) on PGE(2) secretion were seen, even when cells were co-stimulated with AA, to provide enough substrate. COX isotype selective inhibitors were used to discern relative contributions of COX-1 and COX-2 activities to microglial PGE(2) secretion. COX-2 and in part COX-1-selective inhibitors inhibited LPS-induced PGE(2) secretion, whereas the AA-induced PGE(2) secretion was reduced by COX-1-selective inhibitors only. Apparently, adult human microglia in vitro (1) constitutively express COX-1, and (2) do not express COX-2 upon exposure to either Abeta or plaque associated cytokines. In the light of microglial COX activity as a potential therapeutical target in AD, the data presented in this study suggest that classical NSAIDs, rather than selective COX-2 inhibitors, are more potent in reducing microglial prostaglandin secretion.