Molecular mechanisms of enhanced liver tissue repair in moderately diet restricted rats following hepatotoxic challenge with thioacetamide

The objective of this investigation was to establish molecular mechanisms of enhanced liver tissue repair in moderately diet restricted (DR) rats upon challenge with a model hepatotoxicant, thioacetamide. This investigation is based on the hypothesis that diet restricted rats challenged with a normally lethal dose of thioacetamide have more and quicker stimulation of liver cell division and tissue repair than do ad libitum (AL) rats, due to timely up-regulation of promitogenic signaling mechanisms. Moderately diet restricted (35% for 21 days) male Sprague-Dawley rats exhibit higher survival [70% in DR vs. 10% in AL] after normally lethal thioacetamide (TA)-induced liver injury in spite of a 2.5-fold greater liver injury compared to AL rats due to the enhanced liver cell division and tissue repair after TA treatment. Five different signaling pathways known to be involved in replacement of lost liver tissue were studied in this model. Two cytokine pathways, TNF-α/TNFR I and IL-6/IL-6 R pathway and two growth factor pathways, MAPK (TGF-α/EGFR) and HGF/c-met were studied. Involvement of the free radical nitric oxide (NO) was studied by estimating the activity of the NO-producing enzyme, inducible nitric oxide synthase (iNOS) in the liver tissue.; DR had higher plasma and liver IL-6 coinciding with higher STAT-3 activation after TA treatment. Liver levels of TGF-α and HGF were increased in DR rats coinciding with higher cell division. DR rats had higher expression of EGF receptor which remained up-regulated throughout the time course along with up-regulation of p38 MAPK and ERK1/2 proteins. c-met Protein was higher in DR rats compared to AL controls at 48 hr after TA, a time point at which HGF was higher in DR rats. Diet restriction alone increased iNOS activity 2-fold which might play an important role in early priming of hepatocytes for division. Apoptosis was substantially higher in DR rats after TA challenge than in AL rats, which further augments efficiency of tissue repair by removing damaged and weak cells that might otherwise contribute to progression of liver injury.; Proteomic analysis conducted using two dimensional gels combined with MALDI-MS indicated that expression of 45 proteins was increased three-fold or more in DR rats as compared to AL rats. Following the high dose of TA, 39 proteins were induced more than 3-fold in DR rats as compared to AL rats.; Taken together, these data indicate that the enhanced compensatory liver tissue repair in the DR rats is due to timely and augmented pro-mitogenic signaling via cytokines and growth factors in DR rats following toxic challenge with TA.