To improve liposome-directed therapy of liver disease and gene delivery, it would be beneficial to selectively target hepatocytes. For this purpose, conventional liposomes (CL) were labeled with asialofetuin (AF), an asialoglycoprotein. The biodistribution of AF-labeled liposomes (AF-L) in mice and their incorporation into rat hepatocytes, and their potential use in acute liver injury, were investigated. AF-L displayed a quicker plasma clearance than CL, and 25.4%, 2.7%, and 1.2% of the injected dose remained in the plasma versus 47.0%, 26.1%, and 9.5% of CL, respectively at 2, 4, and 20 hours after the injection. Total liver uptake of AF-L (73% ؎ 3.9%) was markedly higher (P F .005) than CL (16.5% ؎ 1.8%) 4 hours after the injection. Liposomal radioactivity (cpm/mg) was greatly enhanced in the liver (11-fold) during the first 4 hours after the administration of 14 C-AF-L, and was much higher than in 14 C-CL-injected mice (1.5-fold).

The mechanisms by which ethanol inhibits hepatocyte proliferation have been a source of some considerable investigation. Our studies have suggested a possible role for tissue transglutaminase (tTG) in this process. Others have shown that tTG has two distinctly different functions: it catalyzes protein cross-linking, which can lead to apoptosis and enhancement of extracellular matrix stability, and it can function as a G protein (G␣ h ). Under that circumstance, we speculated that the cross-linking activity would be decreased and that it would function to enhance hepatocyte proliferation in response to adrenergic stimulation. Ethanol treatment inhibited hepatocyte proliferation and led to enhanced tTG crosslinking activity, whereas treatment of hepatocytes with an ␣1 adrenergic agonist, phenylephrine, enhanced hepatocyte proliferation while decreasing tTG cross-linking. However, phenylephrine treatment of several hepatoma cell lines had no effect on cellular proliferation or tTG cross-linking activity, and of note, Northern blot analysis demonstrated that whereas primary hepatocytes had high levels of the ␣1␤ adrenergic receptor (␣1BAR) mRNA, the hepatoma cell lines did not have this mRNA. When the Hep G 2 cell line was stably transduced with an expression vector containing the ␣1BR cDNA, the cell line responded to phenylephrine treatment with enhanced proliferation and with decreased tTG cross-linking activity. Ethanol treatment of the ␣1BAR-transfected cells suppressed the phospholipase C-mediated signaling pathways, as detected in the phenylephrine-induced Ca 2؉ response. These results suggest that phenylephrine stimulation of hepatocyte proliferation appears to be occurring through the ␣1BAR, which is known to be coupled with the tTG G protein moiety, G␣ h , and that tTG appears to play a significant role in either enhancing or inhibiting hepatocyte proliferation, depending on its cellular location and on whether it functions as a cross-linking enzyme or a G protein.