Objective: Cytokine-induced hepatic serum amyloid A (SAA) synthesis is the critical step in the pathogenesis of AA amyloidosis secondary to rheumatoid arthritis (RA). This study was conducted to provide more insight into the mechanism of SAA production in hepatocytes and its regulation.
Methods: Primary cultured normal human hepatocytes were stimulated with cytokines (IL-1beta, TNF-alpha and IL-6) and the culture supernatants were analysed for the production of SAA. Human hepatocytes, treated or not treated with A77 1726, were stimulated with IL-1beta and the cellular lysates were analysed by immunoblot using anti-phospho-specific mitogen-activated protein kinase (MAPK) and IkappaB-alpha. Acute phase-SAA (SAA1) mRNA expression was analysed by reverse transcription-polymerase chain reaction.
Results: IL-1beta is a most potent inducer of SAA in normal hepatocytes. A77 1726 suppressed the production of SAA in human hepatocytes activated by IL-1beta in a dose-dependent manner (0-50 microM). A77 1726 inhibited IL-1beta-induced p38 and c-Jun N-terminal kinase 1/2 (JNK1/2) activation, whereas A77 1726 did not affect IL-1beta-induced NF-kappaB activation in hepatocytes.
Conclusion: These results indicate that MAPK signalling pathways are critical in IL-1beta-induced hepatic SAA synthesis. Leflunomide may suppress SAA synthesis by affecting these pathways and may therefore have some beneficial effect on AA amyloidosis secondary to RA.