Analysis of the beta-endorphin structure-related activity on human monocyte chemotaxis: importance of the N- and C-terminal

We evaluated the chemotactic activity of beta-endorphin and beta-endorphin-related peptides on human monocytes. We tested beta-endorphin(1-31) and fragments (1-16), (1-17), (1-27) in which the N-terminal of the opioid is preserved, N-acetyl-beta-endorphin(1-31) and fragments (6-31) and (28-31) in which the C-terminal is preserved, and fragment (2-17) that lacks both the N- and C-terminal. The fragments in which the N- and C-terminal were preserved [with the exception of fragment (28-31)] showed a chemotactic effect, while the lack of both terminals deprived the peptides of any activity. Moreover, only the N-terminal-mediated effects were naloxone reversible, while the C-terminal effects were not. These results indicate that while the intact N-terminal is necessary for opioid like effects, both N- and C-terminal can mediate effects on the immune system, thus offering evidence for a nonopioid receptor-mediated effect of opioid peptides on the immune system.