A limited series of synthetic tetrahydroisoquinoline alkaloids reduce inflammatory gene iNOS via inhibition of p-STAT-1 and suppress HMGB1 secretion in LPS-treated mice lung tissue

Tetrahydroisoquinoline alkaloids (THIs) have shown to increase survival and beneficial effect on animal model of sepsis, partly due to heme oxygenase-1 (HO-1) induction. Here, we aimed to compare a limited series of synthesized THIs on HO-1 induction and inhibitory effect of iNOS and COX-2 expression in lipopolysaccharide (LPS)-activated RAW264.7 cells. To the end, most promising compound (THI-61) was tested whether this compound reduces iNOS protein expression and inflammatory markers (HMGB1, TNF-α) in LPS-treated mice lung tissue. The results indicated that N-carbonyl substituted THI seem to affect HO-1 induction depending on which functional group is attached to C1 position. All compounds that reduce LPS-activated NF-κB-luciferase activity showed to preferential inhibition of iNOS/NO but not COX-2/PGE₂ that was partly related to inhibition of STAT-1 phosphorylation. In particular, THI-61 induced translocation of Nrf2 from cytosol into the nucleus by an increased Nrf2-ARE binding activity, and reduced IL-1β production in LPS-activated RAW264.7 cells. The reduced expression of iNOS/NO by THI-61 was reversed by siHO-1RNA-transfection. In LPS-treated mice, THI-61 significantly reduced iNOS protein in lung tissues, and HMGB1 and TNF-α levels in the BALF. We concluded that 1) lipophilic moiety of 1C substituent is much more important in N-carbonyl substituted THI for induction of HO-1, 2) newly synthesized THI-61 may be beneficial for treatment of lung injury.