Approaches and rationale for the selection of a non-rodent species within a low molecular weight, early drug development program

Glutathione S-transferase placental form (GST-P) expression in hepatocyte foci is regarded as a preneoplastic change in rats. We aimed to reveal the contribution of polarized macrophages in development of GST-P-positive pseudolobules (PLs) in chemically-induced rat cirrhosis. F344 rats were injected with thioacetamide (100 mg/kg BW, twice a week, intraperitoneally). Macrophage immunophenotypes and expression of M1-/M2-related factors were analyzed by immunohistochemistry, real-time RT-PCR and laser microdissection. GST-P-positive foci/clusters were clearly observed at post-first injection week 15. GST-P-positive PLs were distinguishable at weeks 20-32. Microarray analysis revealed upregulation of preneoplastic genes in GST-P-positive PLs at week 32. M1 (CD68+, Iba1+)-and M2 (CD163+, CD204+, Gal-3+)-macrophages were greater in number in the GST-P-positive PLs, whereas MHC class II-positive (M1) macrophage number was fewer in the GST-P-positive PLs. Expression of both M1 (IFN-γ, IL-1β, TNF-α, Iba1)- and M2 (IL-4, TGF-β1, IL-10)-related factors were higher in GST-P-positive PLs. Our results showed that both M1- and M2-macrophage populations contribute to the development of hepatic preneoplastic lesions. MHC class II-positive macrophages may be related to anti-tumor progression, since their kinetics showed reverse pattern to other macrophage phenotypes.