Metabolism of dynorphin A1-13 in human CSF.
In-vitro incubation of human cerebrospinal fluid (CSF) obtained from patients ranging from 22-78 years with 10 microM of dynorphin A1-13 (Dyn A1-13) resulted in several cleavage products. Dyn A1-12 and A2-13 were identified as the major CSF metabolites by matrix-assisted laser desorption mass spectrometry (LD-MS). Further metabolites were Dyn A1-6, A2-12 and A4-12. LD-MS further suggested the formation of Dyn A1-8, A1-7, A1-10, A7-10, A3-12, A7-12, A3-13, A7-13 and A8-13. The metabolic half-life of Dyn A1-13 at 37 degrees C was approximately 2.5 h (range 1.75-8.5 h), compared to less than one minute in plasma. The half-life of Dyn A1-13 decreased markedly with age or age-associated processes (n = 20, r2 = 0.498). Noncompartmental kinetic analysis in the absence or presence of enzyme inhibitors (leucinethiol 10 microM, captopril 100 microM and GEMSA 20 microM) suggested that Dyn A1-13 is mainly metabolized by carboxypeptidase to A1-12 (51%) and by aminopeptidases to A2-13 (35%). The generation of A1-6 (13%) was only detected under enzyme inhibition. The extent of conversion into the main metabolites did not follow an age-associated trend, thus over-all enzyme levels but no specific enzymatic systems are elevated with age.
Müller
S
S
College of Pharmacy, University of Florida, Gainesville 32610, USA.
Grundy
B L
BL
Hochhaus
G
G
D000328:Adult; D000368:Aged; D000375:Aging / Q000134:cerebrospinal fluid*; D000626:Aminopeptidases / Q000037:antagonists & inhibitors / Q000378:metabolism; D002268:Carboxypeptidases / Q000037:antagonists & inhibitors / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid; D004399:Dynorphins / Q000097:blood / Q000134:cerebrospinal fluid*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D006207:Half-Life; D006801:Humans; D008297:Male; D013058:Mass Spectrometry; D008875:Middle Aged; D010446:Peptide Fragments / Q000097:blood / Q000134:cerebrospinal fluid*
D004791:Enzyme Inhibitors; D010446:Peptide Fragments; C026843:dynorphin (1-13); D004399:Dynorphins; D002268:Carboxypeptidases; D000626:Aminopeptidases