Hepatic differentiation of human adipose tissue-derived mesenchymal stem cells and adverse effects of arsanilic acid and acetaminophen during in vitro hepatic developmental stage.

In the present study, we differentiated hepatocyte-like cells (HLCs) from human adipose tissue-derived mesenchymal stem cells (AT-MSCs). The hepatic differentiation was confirmed by increases in hepatic proteins or genes, the cytochrome P450 (CYP) activities, albumin secretion, and glycogen storage. To determine the developmental toxic effect of arsanilic acid (Ars) and acetaminophen (AAP) on the hepatic development, the differentiating cells were treated with the test chemicals (below IC12.5) from day 4 to day 13. The enzymatic activities of lactate dehydrogenase (LDH), alanine aminotransferase (ALT), and aspartate aminotransferase (AST) did not significantly differ in response to Ars treatment. AAP treatment increased the activities of all enzymes in a dose-dependent manner, significantly at concentrations of 2.5 and 5 mM of AAP. On the expressions of hepatic genes for Ars, the expressions were significantly inhibited by more than 0.5 mM for Albumin (ALB), but only 2.5 mM for α-feto protein (AFP). In the AAP-treated group, the expressions of ALB and AFP were significantly decreased at the concentrations exceeding 0.625 mM. The activities of CYP3A4 were not changed by both treatments. The activities of CYP1A2 were increased by AAP, whereas it was decreased by Ars treatment. In conclusion, AAP could cause serious adverse effects during the hepatic development as compared to Ars.

Sphingosine kinase inhibitor suppresses IL-18-induced interferon-gamma production through inhibition of p38 MAPK activation in human NK cells.

Natural killer (NK) cells play an important role in the innate immune response. Interleukin-18 (IL-18) is a well-known interferon-gamma (IFN-gamma inducing factor, which stimulates immune response in NK and T cells. Sphingosine kinase (SPHK) catalyzes the formation of sphingosine 1-phosphate (S1P), which acts as a second messenger to function as an anti-apoptotic factor and proliferation stimulator of immune cells. In this study, to elucidate whether SPHK is involved in IL-18-induced IFN-gamma production, we measured IL-18-induced IFN-gamma production after pre-treatment with SPHK inhibitor (SKI) in NK-92MI cells. We found that IL-18-induced IFN-gamma expression was blocked by SKI pre-treatment in both mRNA and protein levels. In addition, the increased IFN-gamma production by stimulation with IL-18 is mediated through both SPHK and p38 MAPK. To determine the upstream signals of SKI and p38 MAPK in IL-18-induced IFN-gamma production, phosphorylation levels of p38 MAPK was measured after SKI pre-treatment. As a result, inhibition of SPHK by SKI blocked phosphorylation of p38 MAPK, showing that SPHK activation by IL-18 is an upstream signal of p38 MAPK activation. Inhibition of SPHK by SKI also inhibited IL-18-induced IFN-gamma production in human primary NK cells. In conclusion, SPHK activation is an essential factor for IL-18-induced IFN-gamma production via p38 MAPK.