High turnover rate of central histaminergic system in patients with Down syndrome and Alzheimer disease

HIGH TURNOVER RATE OF CENTRAL HISTAMINERGIC SYSTEM IN PATIENTS WITH DOWN SYNDROME AND ALZHEIMER DISEASE Maria Concetta Gueli Dipartimento di Biomedicina Sperimentale e Neuroscienze Cliniche (BioNEC), Università degli Studi di Palermo It is well confirmed that a strong relationship exists between Down’s syndrome (DS) and Alzheimer’s disease (AD). Neurochemical investigations reported that many central neurotransmitter systems are similarly affected in aging Down and in Alzheimer patients, respectively. Airaksinem et al. (1) found numerous neurofibrillary tangles in the tuberomammillary area of the hypothalamus, where cell bodies of histaminergic neurons are located. While Mazurkiewicz-Kwilecki et al. (2) found deficits of the endogenous diamine, Cacabelos et al. (3) reported an increase of central histamine levels. In the present study, in order to test whether AD-like neuropathological changes involve the central histaminergic system, we measured the concentration of histamine, histidine as well as the activity of histidine decarboxylase (HDC) and histamine-Nmethyltransferase (HMT) in temporal cortex (TC) of aging Down, Alzheimer and control patients. Post-mortem samples (temporal cortex, TC; grey matter) of AD neuropathologically confirmed cases (72.1 ± 7.6 years old), of karyotyped patients with DS (56.1 ± 7.1 years old), and control adults (72,7 ± 9.7 years old) were obtained from the MRC London Brain Bank for Neurodegenerative Diseases, Department of Neuropathology, Institute of psychiatry, London, U.K. Each block of brain tissue from AD, DS and controls were thawed on ice and homogenized in ice-cold HDC-solution of 0.1 M sodium phosphate buffer (pH 6.8) containing dithiothreitol and antipain protease inhibitor. Homogenates of brain specimens were centrifuged at 12,000 x g for 20 min at 4°C. The supernatants were poured into CENTRIPEP-3 concentrators (Amicon), and centrifuged at 2,000 x g for two 10 min periods at 4°C. The clear extracts were stored in small quantities in Eppendorf tubes at -80°C until analysis. HDC activity has been measured with the procedure described by Gueli et al. (4) and briefly summarized. Extract aliquots were pre-incubated for 10 min with HDC assay-solution (0.1 M PBS, 0.2 mM DTT, 0.01 mM PLP, 0.1 mM Aminoguanidine), then incubation was started by adding 0.5 mM Lhistidine for 0-3 h at 37°C. At the established times, the reactions were stopped with 60 % ice-cold PCA, and stored overnight. Finally, the reaction mixture was centrifuged at 19,000 x g for 30 min at 4°C. The supernatants were withdrawn and filtered (0.45 mm Millipore filter). The HPLC system consisted of a 600E Waters pump with a Waters 474 scanning fluorescence detector (ex 350 nm, em 450 nm). Chromatograms and calculations were performed by Empower TM2 Data Software. Histamine was separated and quantified after pre-column derivatization with Shore’s o-phthalaldehyde reaction (5), using a Spherisorb ODS2 analytical column, particle size 3 mm (20 x 0.46 cm,) (Waters, Milano), a 10 L injection volume, and a mobile phase of methanol, 20 mmol/ L sodium acetate in water, acetic acid (55:43:2 v/v) and 0.33 mmol/L 1- octanesulfonic acid sodium salt. The flow rate was 1.0 ml/min. In order to measure HMT activity brain tissue was disperged with a glass Teflon homogenizer in 0.1 M PBS (pH 7.2). After centrifugation the supernatant was used for the radioenzymatic assay (6). Histidine contents were measured using the procedure described by Borum (7). We observed a increase of histamine levels in temporal cortex of AD (+15%) patients. Down brains also showed a mild increase of the endogenous diamine concentration (+8%). HDC activity in both groups of diseased brains was significantly increased compared with controls (+59% for DS and +21% for AD, respectively). In accord to HDC actvity, HMT activity run in parallel in both pathological groups. In contrast to histamine, histidine levels were markedly decreased in temporal cortex of both pathological groups. These results put together leads us to think of a similar high turnover rate in the metabolic happenings of the histaminergic system in the temporal cortex of the patients with Alzheimer’s disease and Down’s syndrome. The fast histaminergic changes may contribute to the clinical manifestation of dementia in both disorders. (1) Airaksinen, M.S., Paetau, A., Paljarvi, L., Renikainen, K., Riekkinen, P., Suomalainen, R. and Panula, P., Histamine neurons in human hypothalamus: anatomy in normal and Alzheimer diseased brains, Neuroscience, (1991) 9, 465- 481. (2) Mazurkiewicz-Kwilecki, IM., Nsonwah, S., Changes in the regional brain histamine and histidine levels in postmortem brains of Alzheimer patients, Can. J. Physiol Pharmacol., (1989) 67, 75-78. (3) Cacabelos, R., Yamatodani, A., Niigawa, H., Hariguchi, S., Tada, K., Nishimura, T., Wada, H., Brandeis, L. and Pearson, J., Brain Histamine in Alzheimer’s disease, Meth. and Find. Exp. Clin. Pharmacol., (1989) 11, 353-360. (4) Gueli, M.C., The Mental Disords in the Elderly : New Therapeutic Approaches (1997) Rome, 105-106. (5) Shore, P.A., Burkhalter, A., and Cohn, V.H., A method for the fluorometric assay of histamine in tissues, J. Pharmacol. Exp. Ther., (1959) 127 182-186. (6) Prast, H., Gujrati, V., Walser, S., Philippu, A., Histamine, histidine decarboxylase and histamine-N-methyltransferase in brain areas of spontaneously hypertensive rats, Naunyn-Schmiedeberg’s Arch. Pharmacol., (1988) 338, 573-573. (7) Borum, P.R., Manual for Amino Acid Analysis of Physiological Samples. American Association for Clinical Chemistry 37th National Meeting Atlanta, GA. BioNEC, Policlinico “P. Giaccone” Via Del Vespro, 129 90127 Palermo 0916552435 mariac.gueli@unipa.it