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Renin Inhibitors Inhibited the Activity of Recombinant Human Renin but not Activity in Healthy Human Plasma by Masaru Iwai, Izumi Senba, Harumi Kanno, Hirotomo Nakaoka, Shinji Inaba, Masatsugu Horiuchi

Background: Activity of renin substrate cleavage (renin-like activity) was measured in vitro in plasma samples obtained from healthy human volunteers.
Methods: Renin-like activity was determined using FRET (Fluorescence Resonance Energy Transfer) human renin substrate. Recombinant human renin and human plasma showed dose-dependent cleavage activity of FRET human renin substrate.
Results: Activity of recombinant human renin was completely inhibited by either a peptidergic or a non-peptidergic renin inhibitor. However, renin-like activity in human plasma was not inhibited by these renin inhibitors. In a mixture of recombinant renin and human plasma, renin inhibitors inhibited only that part of the activity caused by recombinant renin, while the activity in plasma still remained. Human plasma did not show cleavage activity of rat FRET renin substrate. Native human prorenin showed cleavage activity of human renin substrate. This activety was also completely inhibited by renin inhibitors. Immunoprecipitation with anti-renin or anti-prorenin anti-bodies did not reduce the activity in human plasma. Renin-like activity in human plasma was abolished by degeneration of protein when sample was heated to 95°C. Activity of both recombinant renin and human plasma was significantly inhibited by a protease inhibitor cocktail.
Conclusions: These results suggest that the activity of renin substrate cleavage in human plasma is not mainly caused by the renin or prorenin molecule, but probably by other proteases.

DOI: Clin. Lab. 2012;58:291-298