Primary human hepatocytes (PHH) are the "gold standard" for in vitro toxicity tests. However, 2D PHH cultures have limitations that are due to a time-dependent dedifferentiation process visible by morphological changes closely connected to a decline of albumin production and CYP450 activity. The 3D in vitro culture corresponds to in vivo-like tissue architecture, which preserves functional characteristics of hepatocytes, and therefore can at least partially overcome the restrictions of 2D cultures. Consequently, several drug toxicities observed in vivo cannot be reproduced in 2D in vitro models, for example, the toxic effects of acetaminophen. The objective of this study was to identify molecular differences between 2D and 3D cultivation which explain the observed toxicity response. Our data demonstrated an increase in cell death after treatment with acetaminophen in 3D, but not in 2D cultures. Additionally, an acetaminophen concentration-dependent increase in the CYP2E1 expression level in 3D cultures was detected. However, during the treatment with 10 mM acetaminophen, the expression level of SOD gradually decreased in 3D cultures and was undetectable after 24 h. In line with these findings, we observed higher import/export rates in the membrane transport protein, multidrug resistance-associated protein-1, which is known to be specific for acetaminophen transport. The presented data demonstrate that PHH cultured in 3D preserve certain metabolic functions. Therefore, they have closer resemblance to the in vivo situation than PHH in 2D cultures. In consequence, 3D cultures will allow for a more accurate hepatotoxicity prediction in in vitro models in the future.

The therapeutic value of adipose-derived mesenchymal stem cells (Ad-MSCs) for bone regeneration is critically discussed. A possible reason for reduced osteogenic potential may be an age-related deterioration of the Ad-MSCs. In long term in vitro culture, epigenomic changes in DNA methylation are known to cause gene silencing, affecting stem cell growth as well as the differentiation potential. In this study, we observed an age-related decline in proliferation of primary human Ad-MSCs. Decreased Nanog, Oct4 and Lin28A and increased Sox2 gene-expression was accompanied by an impaired osteogenic differentiation potential of Ad-MSCs isolated from old donors (>60 a) as compared to Ad-MSCs isolated from younger donors (<45 a). 5-hydroxymethylcytosine (5 hmC) and 5-methylcytonsine (5 mC) distribution as well as TET gene expression were evaluated to assess the evidence of active DNA demethylation. We observed a decrease of 5 hmC in Ad-MSCs from older donors. Incubation of these cells with 5-Azacytidine induced proliferation and improved the osteogenic differentiation potential in these cells. The increase in AP activity and matrix mineralization was associated with an increased presence of 5 hmC as well as with an increased TET2 and TET3 gene expression. Our data show, for the first time, a decrease of DNA hydroxymethylation in Ad-MSCs which correlates with donor-age and that treatment with 5-Azacytidine provides an approach which could be used to rejuvenate Ad-MSCs from aged donors.

Smokers frequently suffer from impaired fracture healing often due to poor bone quality and stability. Cigarette smoking harms bone cells and their homeostasis by increased formation of reactive oxygen species (ROS). The aim of this study was to investigate whether Quercetin, a naturally occurring antioxidant, can protect osteoblasts from the toxic effects of smoking. Human osteoblasts exposed to cigarette smoke medium (CSM) rapidly produced ROS and their viability decreased concentration- and time-dependently. Co-, pre- and postincubation with Quercetin dose-dependently improved their viability. Quercetin increased the expression of the anti-oxidative enzymes heme-oxygenase- (HO-) 1 and superoxide-dismutase- (SOD-) 1. Inhibiting HO-1 activity abolished the protective effect of Quercetin. Our results demonstrate that CSM damages human osteoblasts by accumulation of ROS. Quercetin can diminish this damage by scavenging the radicals and by upregulating the expression of HO-1 and SOD-1. Thus, a dietary supplementation with Quercetin could improve bone matter, stability and even fracture healing in smokers.

Primary human hepatocytes (hHeps) are still gold standard to perform human drug metabolism studies, but their availability is limited by donor organ scarcity. Therefore, hepatoma cell lines are widely used as alternatives, although their phases I and II drug-metabolizing activities are substantially lower compared with hHeps. The major advantage of these cell lines is immediate availability, standardized culture conditions and unlimited life span. Therefore, the aim of this study was to investigate the drug-metabolizing profile of five human hepatoma cell lines (HepG2, Hep3B, HCC-T, HCC-M and Huh-7) over a culture period of 10 passages. Fluorescent-based assays for seven different cytochrome P450 (CYP) isoforms and seven different phase II enzymes were performed and compared with enzymatic activities of hHeps. CYP activities were much lower in the cell lines (5-15% of hHeps), whereas phase II enzyme activities that are involved in buffering oxidative stress (e.g., Glutathione-S-transferase) reached levels comparable with hHeps. Furthermore, phases I and II enzyme activities in hepatoma cell lines vary strongly during culture time. Interestingly, the most constant results were obtained with Huh-7 cells. Huh-7 cells as well as HCC-T cells exhibited a drug-metabolizing profile closest to hHeps between passages two and four. Toxicity studies with Diclofenac, Paracetamol and Verapamil in both cell lines show dose-response characteristics and EC(50) values similar to hHeps. Therefore, we propose that due to the more consistent results throughout the passages, Huh-7 could be an alternative system to the limitedly available hHeps and frequently used HepG2 cell line in the study of drug metabolism.