Five out of 16 plasma signaling proteins are enhanced in plasma of patients with mild cognitive impairment and Alzheimer's disease.

Alzheimer's disease (AD) is a progressive neurodegenerative disorder with characteristic neuropathological changes of the brain. Great efforts have been undertaken to determine the progression of the disease and to monitor therapeutic interventions. Especially, the analysis of blood plasma had yielded incongruent results. Recently, Ray et al. (Nat. Med. 13, 2007, 1359f) identified changes of 18 signaling proteins leading to an accuracy of 90% in the diagnosis of AD. The aim of the present study was to examine 16 of these signaling proteins by quantitative Searchlight multiplex ELISA in order to determine their sensitivity and specificity in our plasma samples from AD, mild cognitive impairment (MCI), depression with and without cognitive impairment and healthy subjects. Quantitative analysis revealed an increased concentration in Biocoll isolated plasma of 5 out of these 16 proteins in MCI and AD patients compared to healthy subjects: EGF, GDNF and MIP1δ (in AD), MIP4 (in MCI) and RANTES (in MCI and AD). ROC analysis predicted a sensitivity of 65-75% and a specificity of 52-63% when comparing healthy controls versus MCI or AD. Depression without any significant cognitive deficits did not cause any significant changes. Depressed patients with significant cognitive impairment were not different from MCI patients. In conclusion, we detected a number of altered proteins that may be related to a disease specific pathophysiology. However, the overall expression pattern of plasma proteins could not be established as a biomarker to differentiate MCI from AD or from depression.

Chromogranin peptides in Alzheimer's disease.

Synaptic disturbances may play a key role in the pathophysiology of Alzheimer's disease. To characterize differential synaptic alterations in the brains of Alzheimer patients, chromogranin A, chromogranin B and secretoneurin were applied as soluble constituents for large dense core vesicles, synaptophysin as a vesicle membrane marker and calbindin as a cytosolic protein. In controls, chromogranin B and secretogranin are largely co-contained in interneurons, whereas chromogranin A is mostly found in pyramidal neurons. In Alzheimer's disease, about 30% of beta-amyloid plaques co-labelled with chromogranin A, 20% with secretoneurin and 15% with chromogranin B. Less than 5% of beta-amyloid plaques contained synaptophysin or calbindin, respectively. Semiquantitative immunohistochemistry revealed a significant loss for chromogranin B- and secretoneurin-like immunoreactivity in the dorsolateral, the entorhinal, and orbitofrontal cortex. Chromogranin A displayed more complex changes. It was the only chromogranin peptide to be expressed in glial fibrillary acidic protein containing cells. About 40% of chromogranin A immunopositive plaques and extracellular deposits were surrounded and pervaded by activated microglia. The present study demonstrates a loss of presynaptic proteins involved in distinct steps of exocytosis. An imbalanced availability of chromogranins may be responsible for impaired neurotransmission and a reduced functioning of dense core vesicles. Chromogranin A is likely to be a mediator between neuronal, glial and inflammatory mechanisms found in Alzheimer disease.

Elevated levels of secretoneurin in the rabbit aqueous humor in response to formaldehyde irritation.

BACKGROUND: Secretoneurin, a 33-amino-acid neuropeptide, is generated by proteolytic processing of secretogranin II, which belongs to the chromogranin family. This study aimed to investigate whether secretoneurin is present in the uninflamed rabbit aqueous humor and whether it is released in response to treatment with topical formaldehyde, an agent known to release sensory peptides originating from the trigeminal ganglion. METHODS: Blood samples and aqueous humor of eyes pretreated with neutral formaldehyde and untreated controls were analyzed for secretoneurin immunoreactivity by a highly sensitive radioimmunoassay. Furthermore, the molecular form of the secretoneurin immunoreactivity was characterized by gel filtration high-performance liquid chromatography (HPLC). RESULTS: In the blood, secretoneurin levels were found to be below the detection limit of 2 fmol/100 microl. In the aqueous humor, secretoneurin-immunoreactivity was detected in moderate but significant amounts. The mean concentration of secretoneurin was 8.1 (+/-0.34) fmol/100 microl in controls and 7.8 (+/-0.1) fmol/100 microl 15 min after formaldehyde application. Thirty minutes after treatment, the secretoneurin levels were significantly elevated by 63%. Gel filtration HPLC revealed that the main molecular form corresponded to the free peptide secretoneurin. CONCLUSIONS: The neuropeptide secretoneurin has been detected in the anterior segment of the eye for the first time. The elevation of secretoneurin in formaldehyde-treated eyes may be induced by an enhanced release from the iris/ciliary body complex, as formaldehyde is known to provoke neurogenic inflammation in the anterior segment via release of sensory peptides originating from the trigeminal ganglion. This is why our results indicate a sensory origin of secretoneurin in the eye.

Neural expression and increased lavage fluid levels of secretoneurin in seasonal allergic rhinitis.

Secretoneurin is a neuropeptide potentially involved in migration of eosinophils, monocytes, and dendritic cells. Whether secretoneurin is present in the human airway mucosa and whether it is released at ongoing allergic airway inflammation is currently unknown. In patients with allergic rhinitis, we have explored the occurrence of secretoneurin in nasal mucosal biopsies and lavage fluids before and during natural allergen exposure. Immunohistochemical analysis revealed an abundance of nerves displaying secretoneurin immunoreactivity, which were distributed predominantly around blood vessels and submucosal glands. A majority of nerve fibers containing vesicular acetylcholine transporter, tyrosine hydroxylase, calcitonin gene-related peptide, and vasoactive intestinal peptide were also secretoneurin-immunoreactive, indicating a localization of secretoneurin in cholinergic, adrenergic, and sensory nerves. Lavage fluid levels of secretoneurin were increased at allergen exposure (p < 0.01-0.05). Levels of secretoneurin did not correlate with eosinophil cationic protein (rho = 0.1, p = 0.7). We conclude that secretoneurin has a widespread occurrence in nasal mucosal nerves of patients with seasonal allergic rhinitis and that increased nasal lavage fluid levels of secretoneurin may characterize ongoing allergen exposure. These data favor a role of secretoneurin in the local traffic of immune cells in human airway mucosa.