Specific aminopeptidases of excised human nasal epithelium and primary culture: A comparison of functional characteristics and gene transcripts expression

Objectives: To investigate whether growing human nasal epithelium as primary cultures alters aminopeptidase B (APB), aminopeptidase N (APN) and dipeptidyldipeptidase (DPPIV) metabolic characteristics, and mRNA gene transcript expression. Methods The formation of 7-amino-methyl coumarin from specific substrates for APN (L-alanine-4-methyl-coumaryl-7-amide, APB (L-arginine-4-methyl-coumaryl-7-amide) and DPPIV (glycyl-L-proline-4-methyl- coumaryl-7-amide) was used to estimate the K_M, V_max and the effect of aminopeptidases inhibitors on the enzymes. Polymerase chain reaction was used to investigate gene expression. Key findings: Results of this study showed that: (1) both the excised tissues and primary cultures of human nasal epithelium expressed APN, APB and DPPIV activity; (2) the K_M of APB, APN and DPPIV was not significantly different in cell and tissue homogenates; (3) except for APN, the V_max was not significantly different in the two metabolism models; (4) there was no statistically significant difference in the behaviours of APB, APN and DPPIV in response to inhibition by puromycin and bestatin in the two models; (5) the mRNA transcripts that encode APB, APN and DPPIV were expressed in both cell culture and tissue homogenate. Conclusions: Based on the results of this study, it may be concluded that nasal primary culture system is suitable for investigating peptide and protein metabolism and enzymatic stability in human nasal epithelium. Except for APN, the tissue culture conditions did not significantly alter the functional and molecular expression of the aminopeptidases.