植物甾醇与内毒素协同加重肝巨噬细胞炎症但单独对肝细胞直接作用有限

　　植物甾醇影响胆汁酸转运，促进胆汁淤积，同时可以促进肝巨噬细胞释放促炎因子，诱发加剧炎症反应，最终造成肝脏损伤。为此，美国贝勒医学院儿童营养研究中心、德克萨斯大学西南医学中心儿童医学中心研究所从新生猪仔中提取原代肝细胞及肝巨噬细胞进行体外实验，在培养基中加入不同浓度的植物甾醇或细菌内毒素（LPS）。

　　结果发现，不论在肝细胞还是肝巨噬细胞中，单独使用植物甾醇都不能引起炎症应答改变。但是在炎症诱发物存在的情况下，如LPS共刺激与LPS单刺激相比，植物甾醇可以协同加剧肝巨噬细胞的炎症应答，如IL-1β、TNF-α、IL-6的表达量提升2倍（P＜0.05）。

　　此外，该研究指出植物甾醇可能是通过抑制ATP结合转运体（ABCG5）抑制植物甾醇的转出，以及胆汁酸转出泵（BSEP）抑制胆汁酸转运，加剧炎症反应及胆汁淤积。

JPEN J Parenter Enteral Nutr. 2017;41(2):268-269.

Phytosterols synergize with endotoxin to augment inflammation in kupffer cells but alone have limited direct effect on hepatocytes.

Gregory J. Guthrie, Bryan Tackett, Barbara Stoll, Douglas Burrin.

Pediatrics, Children's Nutrition Research Center, Baylor College of Medicine, Houston, Texas, USA; Children's Medical Center Research Institute UT Southwestern, Dallas, Texas, USA.

PURPOSE: Phytosterols, compounds present in Intralipid (IL), have been shown to alter expression of bile acid export pump, BSEP, which is necessary for normal hepatobiliary transport of bile acids. They have also been shown to induce proinflammatory cytokine release from Kupffer cells following dextran sodium sulfate-mediated intestinal inflammation, which are associated with hepatocellular injury and suppression of phytosterol efflux via the adenosine triphosphate (ATP)-binding cassette transport, ABCG5. Therefore, phytosterol accumulation can lead to liver damage through 2 distinct pathways, accumulation of toxic bile acids and inflammation. The nuclear hormone receptors, farnesoid X receptor (FXR) and the liver X receptor (LXR), are involved in regulation of bile acid homeostasis and inflammation. The aim of this study was to test, first, whether the phytosterols induce inflammation and transport dysfunction directly in hepatocytes and Kupffer cells independently and, second, if the administration of ligands for FXR and LXR can rescue the inflammation-induced suppression of hepatocyte transport dysfunction.

METHODS: Primary hepatocytes and Kupffer cells were isolated from term neonatal piglets using standard collagenase perfusion methods. Cells were incubated in media containing either 0.1% ethanol (control) or media containing 1% Intralipid with increasing concentrations (0-200 μM) of a phytosterol mixture, including β-sitosterol, campesterol, and stigmasterol. After 24-hour incubation, cells were treated with agonists 1 μM obeticholic acid (OCA) or 2 μM GW3695 in the presence or absence of either 50 ng/mL lipopolysaccharide (LPS) or 10 ng/mL interleukin (IL)-1β for 24 hours. Separate studies were performed with 3H-β-sitosterol added to 1% Intralipid media to determine uptake of phytosterols in hepatocytes and Kupffer cells.

RESULTS: We showed that phytosterols mixed with lipid emulsions are taken up in both hepatocytes and Kupffer cells up to 19% and 12%, respectively. In hepatocytes, treatment with Intralipid alone or with increasing phytosterol concentrations did not induce an inflammatory response or change expression of BSEP or ABCG5. Also in hepatocytes, LPS failed to change expression levels of BSEP and ABCG5 but did produce an 8-fold increase in IL-1β, tumor necrosis factor (TNF)-a, and IL-6 gene expression (P < .05). However, IL-1β treatment of hepatocytes led to significant (P < .05) decreases in BSEP (0.36-fold) and ABCG5 (0.35-fold) gene expression. Hepatocyte treatment with either LXR (GW3695) or FXR (OCA) agonists significantly increased (P < .05) BSEP and ABCG5. Yet, cotreatment with both agonist and IL-1β only rescued BSEP gene expression. In Kupffer cells, phytosterol treatment alone did not induce inflammation, but LPS alone significantly (P < .05) increased in cytokine gene expression. Strikingly, when phytosterols were combined with LPS, there was a synergistic 2-fold increase (P < .05) in gene expression of IL-1β, TNF-α, and IL-6 above what was observed with LPS alone.

CONCLUSIONS: Phytosterol exposure alone does not exert an inflammatory response in either hepatocytes or Kupffer cells. However, in the presence of costimulation with an inflammatory insult, like LPS, phytosterols synergistically maximize the inflammatory response in Kupffer cells. Our results suggest a 2-hit mechanism wherein phytosterols may induce hepatocyte dysfunction in vivo via Kupffer cell- and inflammation-dependent cross-talk, leading to suppression of both phytosterol clearance (ABCG5) and bile acid transport (BSEP).

DOI: 10.1177/0148607116686023