Tryptophan hydroxylase and 5-hydroxytryptamine in carcinoids of the gastrointestinal tract
Brinck, U.; Meyer, T.
Anticancer Research 20(4): 2325-2328
2000
ISSN/ISBN: 0250-7005 PMID: 10953292 Document Number: 516421
Background: Tryptophan hydroxylase is the enzyme that catalyzes the formation of 5-hydroxy-L-tryptophan which is the initial and rate-limiting enzyme in the biosynthesis of 5-hydroxytryptamine (serotonin). The aim of this study was to analyze the differential expression of tryptophan hydroxylase and 5-hydroxytryptamine in human gastrointestinal carcinoids. Material and Methods: Primary carcinoids and hepatic carcinoid metastases (n=8) were investigated for the presence of tryptophan hydroxylase, 5-hydroxytryptamine and chromogranin A. Results: Only one of the tumors examined was immunoreactive for tryptophan hydroxylase, as determined by immunohistochemical techniques and Western blot analysis. All carcinoids expressed 5-hydroxytryptamine and chromogranin A. Conclusions: Carcinoids appear to be a heterogeneous group with respect to the expression of this monooxygenase. Based on these results it is proposed that other cells of the intestine are involved in the biosynthesis of 5-hydroxytryptamine precursors taken up by carcinoid tumor cells.