Novel low molecular weight lignins as potential anti-emphysema agents: In vitro triple inhibitory activity against elastase, oxidation and inflammation

No molecule has been found to be effective against emphysema to date primarily because of its complex pathogenesis that involves elastolysis, oxidation and inflammation. We here describe novel unsulfated or sulfated low molecular weight lignins (LMWLs) chemo-enzymatically prepared from 4-hydroxycinnamic acids monomers, as the first potent triple-action inhibitors of neutrophil elastase, oxidation and inflammation. The inhibitory potencies of three different cinnamic acid-based LMWLs were determined in vitro using chromogenic substrate hydrolysis assays, radical scavenging and lung cellular oxidative biomarker reduced glutathione (rGSH) assays, and lung cellular inflammatory biomarker NFκB and IL-8 assays, respectively. Each LWML uniquely displayed triple-action inhibition, among which CDSO3, a sulfated caffeic acid-based LMWL, was most potent. The half-maximal anti-human neutrophil elastase (HNE) potency of CDSO3 was 0.43 μM. This high potency arose from lignin-like oligomerization, which was further potentiated by 6.6-fold due to sulfation. Mechanistically, this elastase inhibition was of mixed-type, time-dependent and more selective to positively charged elastases. The half-maximal anti-oxidative potency of CDSO3 was 3.52 μM, 4.8-fold potentiated from that of the monomer, caffeic acid (CA). In contrast, the half-maximal inhibitory potency to TNFα-induced inflammation was 5–10 μM, despite no activity with the monomer. More intriguingly, this anti-inflammatory activity was essentially identical with different stimuli, okadaic acid and hydrogen peroxide (H2O2), which implied that CDSO3 acts directly on inflammatory cascades within the cells. Overall, oligomerization and sulfation produced or significantly potentiated the activity, in comparison to the monomer. Thus, sulfated and unsulfated LMWLs are novel non-peptidic 2.8–4.1 kDa macromolecules that exhibit for the first time potent triple inhibitory activity against elastase, oxidation and inflammation, the three major pathogenic mechanisms known to cause emphysema.