Neyrinck A
Unité de Pharmacocinétique, Métabolisme, Nutrition et Toxicologie, UCL.
Bull Mem Acad R Med Belg. 2004;159(5-6):358-66.
Classically, the maintenance and control of liver homeostasis are assigned to the metabolic activity of parenchymal cells. However, recent evidence highlights complex and tightly regulated interactions between hepatocytes and other intra-hepatic cells. Kupffer cells--the resident macrophages of the liver--are able to release a tremendous array of mediators upon inflammatory conditions, such as infection, and their role in innate immunity is well described in the literature. However, the impact of these Kupffer cell-derived mediators on liver homeostasis is unknown. In this study, we investigated the physiological involvement of Kupffer cells in the regulation of hepatic metabolism. It was first necessary to validate the use of a compound able to selectively deplete Kupffer cells. We confirmed that gadolinium chloride (GdCl3) injection to rats eliminated ED2-positive Kupffer cells and strongly decreased both their phagocytic and peroxidase activities. Moreover, we demonstrated that precision-cut liver slices (PCLS)--an original in vitro model allowing to maintain intact hepatic architecture and cellular heterogeneity--obtained from GdCl3-treated rats released lower amounts of inflammatory mediators. Therefore, we proposed to use GdCl3 prior to PCLS preparation in order to investigate the role of Kupffer cells in the control of hepatic metabolism. Among various metabolic functions of the liver, we focused, in particular, on paracetamol and lipid metabolism as example of drug and intermediary metabolism, respectively. Our results suggest that the presence of Kupffer cells in liver tissue can affect the viability of PCLS in culture and are involved in the regulation of paracetamol metabolism, in particular the glucuronidation pathway. Furthermore, inhibition of Kupffer cells leads to a metabolic shift of fatty acids towards their esterification (at least, in fasted rats) and accumulation in the liver tissue, supporting a key role of Kupffer cells in the regulation of intra-hepatic lipid metabolism. Results obtained from in vitro studies suggest that Kupffer cell-derived prostaglandin E2 might be involved in the higher capacity of lipid synthesis observed in PCLS obtained from GdCl3-treated rats. Final objectives of this work were devoted to highlight the impact of the diet on Kupffer cell activity, offering possibilities to modulate Kupffer cell functions by nutrients under various physio-pathological conditions, such as inflammation. Our results demonstrate that a supplementation of glycine, a simple amino acid, in the diet could influence lipid metabolism, namely in the liver. A direct relationship between those metabolic effects and Kupffer cell activity has not been demonstrated. Nevertheless, we have shown that the use of glycine in vitro offers the possibility to elucidate complex interactions between Kupffer cells and hepatocytes, by using PCLS in culture, and could constitute an alternative tool to inhibit in vitro Kupffer cell-derived mediators. Furthermore, dietary oligofructose, a fermentable and nondigestible carbohydrate known as prebiotic, was able to increase phagocytic activity of the liver and the production of Kupffer cell-derived mediators by PCLS. Our results indicate that improvement of Kupffer cell activities might be involved in the hepatoprotection against septic challenge observed after a diet enriched with oligofructose.
传统上，肝脏内稳态的维持和调控归因于实质细胞的代谢活动。然而，最近的证据凸显了肝细胞与其他肝内细胞之间复杂且受到严格调控的相互作用。库普弗细胞——肝脏中的常驻巨噬细胞——在诸如感染等炎症条件下能够释放大量的介质，其在固有免疫中的作用在文献中已有详尽描述。然而，这些源自库普弗细胞的介质对肝脏内稳态的影响尚不清楚。在本研究中，我们调查了库普弗细胞在肝脏代谢调控中的生理作用。首先有必要验证一种能够选择性清除库普弗细胞的化合物的用途。我们证实，给大鼠注射氯化钆（GdCl₃）可消除ED2阳性的库普弗细胞，并显著降低其吞噬和过氧化物酶活性。此外，我们证明，从经GdCl₃处理的大鼠获得的精密肝切片（PCLS）——一种能够维持完整肝脏结构和细胞异质性的原始体外模型——释放的炎症介质量较低。因此，我们建议在制备PCLS之前使用GdCl₃，以研究库普弗细胞在肝脏代谢控制中的作用。在肝脏的各种代谢功能中，我们特别关注对乙酰氨基酚和脂质代谢，分别作为药物代谢和中间代谢的例子。我们的结果表明，肝脏组织中库普弗细胞的存在会影响培养中PCLS的活力，并参与对乙酰氨基酚代谢的调控，特别是葡萄糖醛酸化途径。此外，抑制库普弗细胞会导致脂肪酸代谢转向其酯化（至少在禁食大鼠中如此）并在肝脏组织中积累，这支持了库普弗细胞在肝内脂质代谢调控中的关键作用。体外研究获得的结果表明，源自库普弗细胞的前列腺素E2可能参与了从经GdCl₃处理的大鼠获得的PCLS中观察到的较高脂质合成能力。这项工作的最终目标致力于突出饮食对库普弗细胞活性的影响，为在各种生理病理条件（如炎症）下通过营养物质调节库普弗细胞功能提供可能性。我们的结果表明，在饮食中补充甘氨酸（一种简单氨基酸）会影响脂质代谢，特别是在肝脏中。尚未证明这些代谢效应与库普弗细胞活性之间存在直接关系。然而，我们已经表明，在体外使用甘氨酸通过培养PCLS有可能阐明库普弗细胞与肝细胞之间的复杂相互作用，并且可能构成一种抑制体外源自库普弗细胞的介质的替代工具。此外，膳食低聚果糖（一种可发酵且不可消化的碳水化合物，被称为益生元）能够增加肝脏的吞噬活性以及PCLS产生的源自库普弗细胞的介质。我们的结果表明，库普弗细胞活性的改善可能参与了富含低聚果糖的饮食后观察到的对脓毒症挑战的肝脏保护作用。
