Serotonin-immune interactions in elderly volunteers and in patients with Alzheimer's disease (DAT): lower plasma tryptophan availability to the brain in the elderly and increased serum interleukin-6 in DAT.
The aims of this study were to examine the plasma availability of tryptophan, the precursor of 5-hydroxytryptamine (5-HT), and serum cytokines, such as interleukin-6 (IL-6) and IL-8, in normal elderly volunteers and in patients with Alzheimer's disease (DAT). Elderly normal volunteers (mean age = 78.3 +/- 5.7 years) had a significantly lower tryptophan/competing amino acids (valine + leucine + isoleucine + phenylalanine + tyrosine) ratio than younger subjects (mean age = 32.9 +/- 8.1 years). In normal volunteers, there were significant and inverse relationships between age and either plasma tryptophan or the tryptophan/competing amino acids ratio, and between the availability of tryptophan to the brain and serum IL-6 or IL-8. DAT patients had significantly higher serum IL-6, but not IL-8, than age-matched normal volunteers. There 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 plasma tryptophan to the brain decreases with age, and with activation of the immune system; and 2) increased production of IL-6 may play a role in the pathogenesis of DAT.
Bonaccorso
S
S
Clinical Research Center for Mental Health, Antwerp, Belgium.
Lin
A
A
Song
C
C
Verkerk
R
R
Kenis
G
G
Bosmans
E
E
Scharpe
S
S
Vandewoude
M
M
Dossche
A
A
Maes
M
M
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000097:blood / Q000276:immunology* / Q000378:metabolism*; D000544:Alzheimer Disease / Q000097:blood / Q000276:immunology* / Q000378:metabolism*; D001921:Brain / Q000378:metabolism*; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D015850:Interleukin-6 / Q000097:blood*; D016209:Interleukin-8 / Q000097:blood; D008297:Male; D008875:Middle Aged; D012701:Serotonin / Q000378:metabolism*; D014364:Tryptophan / Q000097:blood*
D015850:Interleukin-6; D016209:Interleukin-8; D012701:Serotonin; D014364:Tryptophan