The effects of THI 52 (1-naphthylethyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline) on (a) inducible nitric oxide synthase (iNOS) and tumor necrosis factor-alpha (TNF-alpha) expression in RAW 264.7 cells stimulated by lipopolysaccharide (LPS)/interferon gamma (IFN-gamma), (b) plasma nitrate concentration as well as iNOS protein expression (lung) in vivo in LPS-treated rats, and (c) the restoration of vascular contractility to vasoconstrictor agents in LPS-treated vessels in vitro were investigated. THI 52 concentration-dependently reduced not only nitric oxide (NO) production (IC50 value, 12.5 muM) but also the expression of TNF-alpha and iNOS mRNA in RAW 264.7 cells. Incubation of rat endothelium-denuded thoracic aorta with LPS (300 ng/mL) in vitro for 8 hr resulted in the suppression of vasoconstrictor effects to phenylephrine (PE), effects that were restored by co-incubation with THI 52. Administration of THI 52 (10 and 20 mg/kg, i.p.) 30 min before injection of LPS (10 mg/kg, i.p.) resulted in a significant reduction of the expression of iNOS protein in rat lung tissue and in the plasma nitrite/nitrate (NOx) level. Addition of THI 52-treated macrophage-conditioned medium to a TNF-sensitive L929 fibroblast cell line (CCL1) increased cell viability, depending on the concentration of THI 52. Finally, THI 52 inhibited the activation of nuclear factor kappaB (NF-kappaB) by inhibition of IkappaB degradation through the prevention of IkappaB phosphorylation. Collectively, these results strongly suggest that THI 52 suppresses both TNF-alpha and iNOS gene expression by inhibiting NF-kappaB. Thus, THI 52, a new synthetic isoquinoline alkaloid, may be beneficial in inflammatory disorders where the overproduction of NO and TNF-alpha is a matter of concern. (C) 2002 Elsevier Science Inc. All rights reserved.