PNPLA3对肝细胞和肝癌细胞脂质代谢的影响*

PNPLA3基因在人类和哺乳动物体内都有表达,并且在肝癌细胞中也有表达。PNPLA3在人体和小鼠体内突变后可导致肝细胞内甘油三酯的蓄积,肝细胞发生脂肪变性。在人类和大鼠肝癌细胞使突变型PNPLA3过表达,与过表达野生型PNPLA3细胞比,也会导致肝癌细胞脂质的聚集。本文将归纳总结以往关于PNPLA3基因对肝细胞和肝癌细胞脂质代谢的影响,并分别讨论了PNPLA3对人类肝细胞和肝癌细胞、大鼠和小鼠肝细胞及其肝癌细胞的影响。     

Genetic toxicity assessment using liver cell models: past,present, and future

ABSTRACT

Genotoxic compounds may be detoxified to non-genotoxic metabolites while many pro-carcinogens require metabolic activation to exert their genotoxicity in vivo. Standard genotoxicity assays were developed and utilized for risk assessment for over 40 years. Most of these assays are conducted in metabolically incompetent rodent or human cell lines. Deficient in normal metabolism and relying on exogenous metabolic activation systems, the current in vitro genotoxicity assays often have yielded high false positive rates, which trigger unnecessary and costly in vivo studies. Metabolically active cells such as hepatocytes have been recognized as a promising cell model in predicting genotoxicity of carcinogens in vivo. In recent years, significant advances in tissue culture and biological technologies provided new opportunities for using hepatocytes in genetic toxicology. This review encompasses published studies (both in vitro and in vivo) using hepatocytes for genotoxicity assessment. Findings from both standard and newly developed genotoxicity assays are summarized. Various liver cell models used for genotoxicity assessment are described, including the potential application of advanced liver cell models such as 3D spheroids, organoids, and engineered hepatocytes. An integrated strategy, that includes the use of human-based cells with enhanced biological relevance and throughput, and applying the quantitative analysis of data, may provide an approach for future genotoxicity risk assessment.     

Recent advances in preclinical in vitro approaches towards quantitative prediction of hepatic clearance and drug-drug interactions involving organic anion transporting polypeptide (OATP) 1B transporters

Hepatic uptake mediated by organic anion transporting polypeptide (OATP) 1B1 and 1B3 can serve as a major elimination pathway for various anionic drugs and as a site of drug-drug interactions (DDIs). This article provides an overview of the in vitro approaches used to predict human hepatic clearance (CL_h) and the risk of DDIs involving OATP1Bs. On the basis of the so-called extended clearance concept, in vitro–in vivo extrapolation methods using human hepatocytes as in vitro systems have been used to predict the CL_h involving OATP1B-mediated hepatic uptake. CL_h can be quantitatively predicted using human donor lots possessing adequate OATP1B activities. The contribution of OATP1Bs to hepatic uptake can be estimated by the relative activity factor, the relative expression factor, or selective inhibitor approaches, which offer generally consistent outcomes. In OATP1B1 inhibition assays, substantial substrate dependency was observed. The time-dependent inhibition of OATP1B1 was also noted and may be a mechanism underlying the in vitro–in vivo differences in the inhibition constant of cyclosporine A. Although it is still challenging to quantitatively predict CL_h and DDIs involving OATP1Bs from only preclinical data, understanding the utility and limitation of the current in vitro methods will pave the way for better prediction.     

Cost-effective differentiation of hepatocyte-like cells from human pluripotent stem cells using small molecules

Significant efforts have been invested into the differentiation of stem cells into functional hepatocyte-like cells that can be used for cell therapy, disease modeling and drug screening. Most of these efforts have been concentrated on the use of growth factors to recapitulate developmental signals under in vitro conditions. Using small molecules instead of growth factors would provide an attractive alternative since small molecules are cell-permeable and cheaper than growth factors. We have developed a protocol for the differentiation of human embryonic stem cells into hepatocyte-like cells using a predominantly small molecule–based approach (SM-Hep). This 3 step differentiation strategy involves the use of optimized concentrations of LY294002 and bromo-indirubin-3’-oxime (BIO) for the generation of definitive endoderm; sodium butyrate and dimethyl sulfoxide (DMSO) for the generation of hepatoblasts and SB431542 for differentiation into hepatocyte-like cells. Activin A is the only growth factor required in this protocol. Our results showed that SM-Hep were morphologically and functionally similar or better compared to the hepatocytes derived from the growth-factor induced differentiation (GF-Hep) in terms of expression of hepatic markers, urea and albumin production and cytochrome P450 (CYP1A2 and CYP3A4) activities. Cell viability assays following treatment with paradigm hepatotoxicants Acetaminophen, Chlorpromazine, Diclofenac, Digoxin, Quinidine and Troglitazone showed that their sensitivity to these drugs was similar to human primary hepatocytes (PHHs). Using SM-Hep would result in 67% and 81% cost reduction compared to GF-Hep and PHHs respectively. Therefore, SM-Hep can serve as a robust and cost effective replacement for PHHs for drug screening and development.     

克霉唑抗肝缺血-再灌注损伤凋亡机制的研究*

目的观察孕烷X受体(PXR)诱导药克霉唑对肝脏缺血-再灌注损伤后肝细胞凋亡影响,并探讨其机制。方法建立大鼠肝脏缺血-再灌注模型,32只雄性SD大鼠随机分为假手术组,模型对照组和克霉唑小剂量组、大剂量组进行肝缺血-再灌注损伤。TUNEL法检测肝组织中凋亡细胞,Western blot检测肝脏CYP3A1、Bcl-2、Bax、PARP表达水平。结果克霉唑小剂量组、大剂量组与模型对照组比较,细胞凋亡数减少,组织损伤减轻,凋亡细胞百分率明显降低,Bcl-2/Bax比值明显升高,抑制PARP剪切,提示有较好的抗凋亡作用,均差异有统计学意义;作为PXR特异性强诱导药克霉唑,与假手术组比,能明显诱导CYP3A1基因表达。结论PXR特异性强诱导药克霉唑可能通过促进Bcl-2表达及抑制Bax表达而拮抗肝细胞凋亡,从而减轻肝脏缺血-再灌注损伤,也与抑制PARP剪切有关。     

外源性硫化氢对肝细胞NLRP3炎症小体的影响

目的:研究外源性硫化氢(H_2S)对人肝细胞NLRP3炎症小体的影响。方法:采用不同浓度的脂多糖(LPS)诱导人肝细胞L02和SMMC-7721建立炎症模型,Western blot检测细胞中NLRP3炎症小体的表达并结合细胞毒性实验(MTT法)确定合适的LPS浓度。细胞分为4组:对照组用普通培养基培养18.5 h;LPS组用普通培养基培养0.5 h后,再用100μg/L LPS刺激18 h;LPS+H_2S组和H_2S组用200μmol/L硫氢化钠(Na HS)刺激0.5 h后,再分别用100μg/L LPS和普通培养基培养18 h。各组处理后分别收集细胞,Western blot检测细胞中NLRP3和caspase-1的蛋白表达量。结果:与对照组相比,LPS组细胞内NLRP3和caspase-1的表达增加(P0.05),H_2S组细胞内的NLRP3和caspase-1表达无明显变化;与LPS组相比,LPS+H_2S组细胞内的NLRP3和caspase-1表达减少(P0.05)。结论:外源性H_2S可抑制人肝细胞中NLRP3炎症小体的表达。     

Adenosine 5＇triphosphate transport and accumulation during the cold preservation of rat hepatocytes in University of Wisconsin solution

AIM: We used isolated hepatocytes to investigate how different concentrations of ATP in the University of Wisconsin (UW) solution affected both cellular ATP content and cell viability during the cold storage and the rewarming step. The mechanism involved in ATP transport and accumulation in hypothermia was also determined. METHODS: The cells were preserved up to 72 h in different conditions: UW solution without ATP (a-group), UW+5 mmol/L ATP (b-group), and UW+10 mmol/L ATP (c-group). The ATP content and the cell viability (LDH release) were determined during the cold storage and the rewarming step. In the groups a and c, the respiratory function of the cells at rewarming was studied. In addition, the cell volume of hepatocytes and the mechanism involved in ATP transport and accumulation were assessed. The extracellular degradation of exogenous nucleotides during transport experiments was investigated by a HPLC technique. RESULTS: After three days of cold storage a loss of cellular ATP content was observed in hepatocytes preserved either without nucleotides (a-group) or with 5 mmol/L ATP (b-group). In contrast, 10 mmol/L ATP (c-group) was able to maintain a normal ATP cellular content, with only a 6% diminution after 72 h of cold storage. The respiratory function was significantly different in hepatocytes preserved with 10 mmol/L ATP than without ATP. No significant change was detected For the three groups in cellular volume during the cold storage. We also report that the time course accumulation of [3H]-ATP by cold stored hepatocytes is a rapid process that is completed after 180 s with linear dependence on the extracellular ATP concentration (linear fitting results in a slope of 0.5624±0.1179 mmol/L ATP intracell/mmcl/L ATP extracell). CONCLUSION: Our results show that, during hypothermic storage in UW solution, hepatocytes are permeable to ATP by a diffusive mechanism. Also, we found that it is ATP the main extracellular nucleotide available for transport and it is not the breakdown products.     

Determination of DNA single strand breaks and selective DNA amplification by N-nitrodimethylamine and analogs,and estimation of the indicator cells' metabolic capacities

Summary N-nitrodimethylamine is metabolized oxidatively to N-nitrohydroxymethylmethylamine, which decomposes to yield formaldehyde and N-nitromethylamine. All four compounds and N-nitroethylamine were tested for their ability to induce DNA single strand breaks in hepatocytes and in SV 40-transformed Chinese hamster embryo cell lines. Only the two monoalkylnitramines were positive. They induced single strand breaks in hepatocytes, but were not effective in the other cells. Formaldehyde and N-nitrohydroxymethylmethylamine were toxic to the cells. None of the compounds tested was able to induce selective DNA amplification in the two transformed cell lines.Enzymes involved in drug metabolism were assayed in the hamster cell lines. The activity of UDP-glucuronosyltransferase and cytosolic epoxide hydrolase were not detectable. N-nitrodimethylamine demethylation was low. The content of reduced glutathione and the activities of glutathione transferase and membrane bound epoxide hydrolase were comparable to values obtained in the rat liver.Dedicated to Professor Dietrich Schmähl on the occasion of his 60th birthday     

HCV体内感染裸鼠模型的建立

目的:探讨利用裸鼠建立感染丙型肝炎病毒(HCV)体内动物模型的可能性。方法:将体外感染了HCV的人胎肝细胞(HFH)移植到裸鼠脾脏。移植术后3个月,取脾作病理学检查,以评估感染了HCV的HFH是否还存活。并且通过透射电镜检查,以评估移植入裸鼠脾脏的HFH胞浆中是否仍有HCV。同时,取裸鼠的外周血液作液相RT-PCR检查,以明确外周血液中HCV RNA是否为阳性。结果:移植术后3个月,移植入裸鼠脾脏内的HFH依然存活,经检查移植入裸鼠脾脏中的HFH胞浆内仍然存在HCV样颗粒。然而,体内有HCV感染的裸鼠外周血液仅70％HCV RNA为阳性。结论:裸鼠可作为“活试管”,支持体外感染了HCV的HFH在其脾脏内较长期生存。但仅使用外周血液HCV RNA检查这一个指标来判断裸鼠体内是否有HCV感染是不够的。     

Ethanol-induced hepatic autophagy: Friend or foe?

Excessive alcohol intake may induce hepatic apoptosis, steatosis, fibrosis, cirrhosis and even cancer. Ethanol-induced activation of general or selective autophagy as mitophagy or lipophagy in hepatocytes is generally considered a prosurvival mechanism. On the other side of the coin, upregulation of autophagy in non-hepatocytes as stellate cells may stimulate fibrogenesis and subsequently induce detrimental effects on the liver. The autophagic response of other non-hepatocytes as macrophages and endothelial cells is unknown yet and needs to be investigated as these cells play important roles in ethanol-induced hepatic steatosis and damage. Selective pharmacological stimulation of autophagy in hepatocytes may be of therapeutic importance in alcoholic liver disease.