Dietmar Fuchs — Page 7

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Association of hyperhomocysteinemia in Alzheimer disease with elevated neopterin levels.

In patients with dementias including Alzheimer disease (AD), elevated blood concentrations of homocysteine are common, often going along with low normal folate and vitamin B12. Immune activation leading to oxidative stress also seems to play an important role in the pathogenesis of AD. To find out a possible relationship between immune activation and the development of moderate hyperhomocysteinemia, we determined serum concentrations of homocysteine, folate, vitamin B12 and immune activation markers 75 kD soluble TNF receptor (sTNF-R75) and neopterin in 38 patients with clinically diagnosed AD. A subgroup of patients (45%) presented with increased homocysteine concentrations in comparison to reference ranges in healthy controls of similar age. Also, concentrations of immune activation markers were elevated in a significant proportion of patients. In 17 patients with moderate hyperhomocysteinemia, concentrations of neopterin were higher than in those with lower homocysteine (p < 0.001). Homocysteine correlated with folate (rs= -0.43; p < 0.01) and neopterin (rs= 0.506; p < 0.001). The data suggest that immune activation and concomitant production of reactive oxygen species in patients with AD could be involved in the development of hyperhomocysteinemia via an enhanced decomposition of folate.

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Retinal pigment epithelial phagocytosis and metabolism differ from those of macrophages.

The purpose of this study is to compare primary human retinal pigment epithelium (RPE) cells with respect to particle uptake and further processing steps with immunological phagocytes for a better understanding of the possible role of RPE cells in triggering autoimmune diseases in the eye. We investigated the similarities of human RPE and monocytes/macrophages studying the uptake of fluorescein- and europium-labeled synthetic microparticles and microbial pathogens by human and bovine RPE cultures and a permanent RPE cell line (CRL). The uptake was monitored by laser scanning microscopy, flow cytometry and time-resolved fluorescence analysis; for comparison, macrophages and a macrophage-like cell line (MonoMac6) were used. A size-dependent uptake was seen in primary RPE cultures as well as in CRL, showing a preferential uptake of smaller beads followed by Staphylococcus aureus and Escherichia coli. Opsonization with serum caused a modest increase in bacteria uptake, but in contrast to macrophages, the classical complement receptors were not found on RPE cells. Living bacteria were also ingested in a time-dependent manner, but, as no intracellular overgrowth was observed, we further investigated the oxidative ability of RPE as a possible mechanism for microbial suppression. Unlike macrophages/granulocytes, no respiratory burst was detected in RPE cells, but, comparable to MonoMac6, IFN-gamma induced neopterin in the human RPE. Interestingly a diurnal rhythm of phagocytosis was observed which was influenced by light exposure suggesting that RPE cells maintain their circadian rhythm also in cell culture to a certain extent. This study further demonstrates that in addition to similar phagocytic properties the RPE still shows substantial metabolic differences in comparison to blood-derived phagocytes.

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