Enzymatic degradation of luteinizing hormone releasing hormone (LHRH)/[D-Ala6]-LHRH in lung pneumocytes.
OBJECTIVE
To investigate the cellular proteolytic activities of various lung pneumocytes using luteinizing hormone releasing hormone (LHRH) and [D-Ala6]-LHRH as model peptide substrates.


METHODS
HPLC analysis was used to investigate the degradation kinetics of LHRH/[D-Ala6]-LHRH and to identify their degradation products in isolated lung pneumocytes.


RESULTS
Pulmonary macrophages exhibited the strongest proteolytic activity against LHRH)/[D-Ala6]-LHRH, followed by type II and type I-like pneumocytes. Three major degradation products of LHRH, namely LHRH 4-10, LHRH 6-10, and LHRH 7-10, were identified in macrophages and type II pneumocytes, whereas in type I-like pneumocytes only the LHRH 7-10 was found. Co-incubation of the cells with known enzyme inhibitors including captopril (an ACE inhibitor), thiorphan (an EP24.11 inhibitor), and EDTA (an EP24.15 inhibitor) inhibited the formation of LHRH 4-10, LHRH 7-10, and LHRH 6-10 respectively. In all cell types, the degradation rate of [D-Ala6]-LHRH was about 3-8 times lower than that of LHRH. This peptide analog was resistant to degradation by EP24.15 and EP24.11, but was susceptible to ACE.


CONCLUSIONS
ACE, EP24.11, and EP24.15 are the major enzymes responsible for the degradation of LHRH in macrophages and type II pneumocytes. The magnitude of peptidase activities in these cell types are: EP24.15 > EP24.11 approximately ACE. No EP24.15 or ACE activity was observed in type I-like pneumocytes and only a weak EP24.11 activity was detected.
Yang
X
X
Department of Basic Pharmaceutical Sciences, West Virginia University, School of Pharmacy, Health Sciences Center, Morgantown 26506, USA.
Rojanasakul
Y
Y
Wang
L
L
Ma
J Y
JY
Ma
J K
JK
D000818:Animals; D002478:Cells, Cultured; D002851:Chromatography, High Pressure Liquid; D004847:Epithelial Cells / Q000378:metabolism; D007987:Gonadotropin-Releasing Hormone / Q000031:analogs & derivatives / Q000378:metabolism*; D008168:Lung / Q000166:cytology / Q000201:enzymology / Q000378:metabolism*; D016676:Macrophages, Alveolar / Q000378:metabolism; D008297:Male; D010447:Peptide Hydrolases / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D013379:Substrate Specificity
D007987:Gonadotropin-Releasing Hormone; D010447:Peptide Hydrolases