Helium as an In Vitro Furin Inhibitor

Beihl, David

Aims Certain cancers, pathogenic infections, and other diseases are facilitated by the host enzyme furin, a calcium-dependent serine protease that is the most prominent member of the family of proprotein convertases. Furin and the other proprotein convertases modify certain other proteins to change them from their inactive to active forms. Previous attempts to find an effective, non-toxic furin inhibitor to treat diseases facilitated by furin have had only limited success, due to toxicity or large molecular size that impedes absorption of the molecule. This has placed increased importance on the development of small-molecule furin inhibitors. The object of this study was to consider the effect of the noble gas helium as a furin inhibitor. Methods This study uses a fluorometric furin inhibition assay to compare the enzymatic activity of recombinant human furin after exposure to balloon-grade helium gas, compared to the enzymatic activity of untreated recombinant human furin. Results Helium exposure was found to decrease the in vitro enzymatic activity of recombinant human furin by as much as 55%; this inhibition lasted for up to 16 hours. Fluorescence measurements of enzymatic activity were taken for 24 hours. Conclusions These findings appear to be the first to report helium as a partial furin inhibitor. The observed partial inhibition was consistent throughout the experiment. The effectiveness of helium as a partial furin inhibitor, its favorable side-effect profile, and its long history of safe use in respiratory therapy, when mixed with 20% oxygen or more and administered under direct medical supervision, make it a promising treatment for diseases facilitated by furin or its substrates. Further studies in cell culture or clinical trials may expand its clinical role for such diseases.