Z Gastroenterol 2010; 48 - P1_23
DOI: 10.1055/s-0029-1246354

Inhibitory effects of 1,7-dimethylxanthine (paraxanthine) on TGF-beta (Smad2/3) signaling in transdifferentiating rat hepatic stellate cells

B Lahme 1, OA Gressner 1
  • 1Institut für Klinische Chemie und Pathobiochemie, Universitätsklinikum der RWTH Aachen, Aachen

Background and Aim: Based on reports of a hepatoprotective effect of coffee consumption, we were the first to give evidence that caffeine suppresses TGF-β dependent Smad signaling and target gene (e.g. CTGF) induction in hepatocytes. Ongoing investigations finally identified the primary caffeine metabolite paraxanthine (1,7-dimethylxanthine; 1,7-DMX) as the most potent xanthine-derived inhibitor of TGF-β signaling in PC, but its effect on TGF-β signaling in hepatic stellate cells (HSC) was not yet investigated.

Methods: HSC were isolated by the pronase-collagenase perfusion technique, and treated with different concentrations of 1,7-DMX for 24h, or left untreated, before being harvested at time points 1, 2, 5 and 15 of culture. CTGF, α-smooth muscle actin (αSMA), and collagen α1 type 1 (Col1) expression was investigated by Western Blot analysis and CTGF luciferase gene reporter assays were performed.

Results: CTGF was increasingly expressed during transdifferentiation with enforced cleavage of the full length molecule in MFB, resulting in an additional fragment of ~18 kDa. Results furthermore showed a transdifferentiation dependent inhibitory effect of paraxanthine on CTGF expression in HSC, being particularly effective in the progressive stage of transdifferentiation. A representative hCTGF-luciferase reporter assay performed in 5 day old HSC confirmed their responsiveness towards paraxanthine also on the transcriptional level. This reduction of CTGF expression was furthermore accompanied by a continuous, paraxanthine dependent, reduction of expression of Col1 but not of αSMA throughout the entire process of transdifferentiation.

Conclusions: Our results suggest a suitability of paraxanthine in antagonizing transdifferentiation dependent sensitization of HSC towards TGF-β (Smad2 and Smad3) dependent effects, i.e. CTGF and Col1 expression. Further investigations in this direction are on the way.