SEROTONIN-IMMUNE INTERACTIONS IN ELDERLY VOLUNTEERS AND IN PATIENTS WITH ALZHEIMERS-DISEASE (DAT) - LOWER PLASMA TRYPTOPHAN AVAILABILITY TOTHE BRAIN IN THE ELDERLY AND INCREASED SERUM INTERLEUKIN-6 IN DAT

The aims of this study were to examine the plasma availability of tryp tophan, the precursor of 5-hydroxytryptamine (5-HT), and serum cytokin es, such as interleukin-6 (IL-6) and IL-8, in normal elderly volunteer s and in patients with Alzheimer's disease (DAT). Elderly normal volun teers (mean age = 78.3 +/- 5.7 years) had a significantly lower trypto phan/competing amino acids (valine + leucine + isoleucine + phenylalan ine + tyrosine) ratio than younger subjects (mean age = 32.9 +/- 8.1 y ears). In normal volunteers, there were significant and inverse relati onships between age and either plasma tryptophan or the tryptophan/com peting amino acids ratio, and between the availability of tryptophan t o the brain and serum IL-6 or IL-8. DAT patients had significantly hig her serum IL-6, but not IL-8, than age-matched normal volunteers. Ther e were no significant differences in the availability of tryptophan to the brain between DAT patients and age-matched normal volunteers. The : results suggest that: 1) in normal humans, the availability of plasm a tryptophan to the brain decreases with age, and with activation of t he immune system; and 2) increased production of IL-6 may play a role in the pathogenesis of DAT. (Aging Clin. Exp. Res. 10: 316-323, 1998) (C) 1998, Editrice Kurtis.