Engagement of the mast cell high-affinity receptor for immunoglobulin E (IgE) Allergen-induced activation of the high-affinity receptor for IgE (FcRI) in mast cells and basophils plays a pivotal role in the initiation of allergic and inflammatory reactions. As a result of receptor engagement, mast cells and basophils release a variety of inflammatory mediators, such as histamine, arachidonic acid metabolites, and cytokines (1, 2). The activation of protein tyrosine kinases (PTKs) is one of the early and critical signaling events following FcRI engagement (3). Since FcRI belongs to the family of multisubunit antigen receptors that do not possess intrinsic PTK activity in their structure (1), the recruitment and activation of non-receptor PTKs is crucial for FcRI-mediated signal transduction (4).,FcRI is a tetrameric receptor composed of an ␣ subunit, a ␤ subunit, and a homodimer of disulfide-linked ␥ subunits (5). The cytoplasmic domains of ␤ and ␥ subunits contain sequences known as the immunoreceptor tyrosine-based activation motifs (ITAMs) (6, 7). The phosphorylation of the tyrosines of the ITAM allows the interaction of ITAMcontaining receptors with signaling proteins that have phosphotyrosine-recognizing Src homology 2 (SH2) domains (8, 9).

Hepatocyte growth factor (HGF) is an endogenously expressed bioactive substance that has a strong anti-apoptotic effect. In this study, we biochemically and histologically characterized the effects of rh-HGF on in vitro human hepatocyte injury and mouse acute liver failure (ALF) models, both of which were induced by antibody-mediated Fas signaling. rh-HGF inhibited intracellular caspase-3/7 activation and cytokeratin 18 (CK-18) fragment release in both models. Histologically, rh-HGF dramatically suppressed parenchymal damage and intrahepatic hemorrhage. Among the laboratory parameters, prothrombin time (PT) was strongly preserved by rh-HGF, and PT was well correlated with the degree of intrahepatic hemorrhage. These results showed that the anti-apoptotic effect of rh-HGF on hepatocytes coincided strikingly with the suppression of intrahepatic hemorrhage. PT was considered to be the best parameter that correlated with the intrahepatic hemorrhages associated with hepatocellular damage. The action of rh-HGF might derive not only from its anti-apoptosis effects on liver parenchymal cells but also from its stabilization of structural and vasculature integrity.

Background: Hepatocyte growth factor (HGF) is an endogenously induced bioactive molecule that has strong anti-apoptotic and tissue repair activities. In this research, we identified APOA4 as a novel pharmacodynamic (PD) marker of the recombinant human HGF (rh-HGF), E3112. Methods: rh-HGF was administered to mice, and their livers were investigated for the PD marker. Candidates were identified from soluble proteins and validated by using human hepatocytes in vitro and an animal disease model in vivo, in which its c-Met dependency was also ensured. Results: Among the genes induced or highly enhanced after rh-HGF exposure in vivo, a soluble apolipoprotein, Apoa4, was found to be induced by rh-HGF in the murine liver. By using primary cultured human hepatocytes, the significant induction of human APOA4 was observed at the mRNA and protein levels, and it was inhibited in the presence of a c-Met inhibitor. Although mice constitutively expressed Apoa4 mRNA in the small intestine and the liver, the liver was the primary organ affected by administered rh-HGF to strongly induce APOA4 in a dose- and c-Met-dependent manner. Serum APOA4 levels were increased after rh-HGF administration, not only in normal mice but also in anti-Fas-induced murine acute liver failure (ALF), which confirmed the pharmacodynamic nature of APOA4. Conclusions: APOA4 was identified as a soluble PD marker of rh-HGF with c-Met dependency. It should be worthwhile to clinically validate its utility through clinical trials with healthy subjects and ALF patients.