细胞色素P450调节肝脏药物代谢的途径

大量研究认为细胞色素P450与药物性肝损伤的病理生理过程密切相关,对其在肝损伤的作用已成为当前研究的一个热点.主要介绍细胞色素P450与药物性肝损伤的相关研究进展.     

肝康Ⅳ号对脂肪肝大鼠肝组织脂质含量及形态学的影响

目的探讨肝康Ⅳ号（Gankang Ⅳ,GKⅣ）对脂肪肝（FL）组织胆固醇（TC）、甘油三脂（TG）、超氧化物歧化酶（SOD）、丙二醛（MDA）及形态学的影响。方法64只SPF级Wistar大鼠,随机分为A组、B1组、B2组、B3组、C组、D组。A组、B1组、B2组、B3组、C组给予高脂饲料（84.4%标准饲料＋10%猪油＋0.5%胆固醇＋0.1%胆盐＋5%蛋黄粉）和白酒复合复制大鼠FL模型,B1组、B2组、B3组、C组分别给予肝康Ⅳ号低、中、高剂量和东宝肝泰灌胃干预,设空白对照D组。第6周末处死动物取肝脏制备10%的肝匀浆检测TC、TG、SOD、MDA。检测肝脏病理学。结果（1）TC、TG：B1组、B2组、B3组、C组与A组比较,TC、TG含量明显下降（P〈0.05～0.01）,B2组、B3组与C组比较差异有显著（P〈0.05）。（2）SOD、MDA：B1组、B2组、B3组、C组与A组比较,MDA含量明显下降（P〈0.05～0.01）,SOD水平明显升高（P〈0.05～0.01）;在SOD方面,B1组与C组比较差异有非常显著性（P〈0.01）,B2组与C组比较差异有显著（P〈0.05）;在MDA方面,B1组、B2组、B3组与C组比较差异有非常显著性（P〈0.01）。（3）肝脏病理学：A组为重度脂肪肝,C组、B1组为中度脂肪肝,B2组、B3组脂肪肝程度轻于C组、B1组。结论GKIV能有效降低肝脏组织脂质沉积,防止MDA的升高,SOD的下降;减轻FL程度,呈现量效关系。     

肿瘤研究的金钥匙:肿瘤干细胞

“肿瘤干细胞学说”认为肿瘤组织不是均一的,其中只有一小部分肿瘤干细胞具有诱发并维持肿瘤恶性表达的能力。这一概念的提出为肿瘤真正意义上的靶向治疗找到了良方妙药,即选择性杀伤肿瘤干细胞从而治愈肿瘤。找到肿瘤干细胞并了解其生物学特性对我们真正理解肿瘤的发生、发展和转归机制,根治肿瘤并防止肿瘤的转移和复发具有积极意义。本文概述对人淋巴细胞白血病、乳腺肿瘤、脑部肿瘤及其他肿瘤的肿瘤干细胞及其相关机制的研究进展。     

Plant sterols and stanols: effects on mixed micellar composition and LXR (target gene) activation

Plant stanols and sterols of the 4-desmethyl family (e.g., sitostanol and sitosterol) effectively decrease LDL cholesterol concentrations, whereas 4,4-dimethylsterols (alpha-amyrin and lupeol) do not. Serum carotenoid concentrations, however, are decreased by both plant sterol families. The exact mechanisms underlying these effects are not known, although effects on micellar composition have been suggested. With a liver X receptor (LXR) coactivator peptide recruitment assay, we showed that plant sterols and stanols from the 4-desmethylsterol family activated both LXRalpha and LXRbeta, whereas 4,4-dimethyl plant sterols did not. In fully differentiated Caco-2 cells, the functionality of this effect was shown by the increased expression of ABCA1, one of the known LXR target genes expressed by Caco-2 cells in measurable amounts. The LXR-activating potential of the various plant sterols/stanols correlated positively with ABCA1 mRNA expression. Reductions in serum hydrocarbon carotenoids could be explained by the effects of the 4-desmethyl family and 4,4-dimethylsterols on micellar carotenoid incorporation. Our findings indicate that the decreased intestinal absorption of cholesterol and carotenoids by plant sterols and stanols is caused by two distinct mechanisms.     

Estradiol enhances cell-associated paraoxonase 1 (PON1) activity in vitro without altering PON1 expression

PON1 is a high density lipoprotein-associated enzyme that plays an important role in organophosphate detoxification and prevention of atherosclerosis. In vivo animal and human studies have indicated that estradiol (E2) supplementation enhances serum PON1 activity. In this study, we sought to determine if E2 directly up-regulates cell-associated PON1 activity in vitro and to characterize the mechanism of regulation. In vitro E2 treatment of both the human hepatoma cell line Huh7 and normal rat hepatocytes resulted in a 2- to 3-fold increase in cell-associated PON1 catalytic activity. E2 potently induced PON1 activity with average EC₅₀ values of 15 nM for normal hepatocytes and 68 nM for Huh7. The enhancement of PON1 activity by E2 was blocked by the estrogen receptor (ER) antagonist ICI 182,780 indicating that E2 was acting through the ER. The up-regulation of PON1 activity by E2 did not involve enhancement of PON1 mRNA or protein levels and did not promote secretion of PON1. Thus, E2 can enhance cell-associated PON1 activity in vitro without altering PON1 gene expression or protein level. Our data suggest that E2 may regulate the specific activity and/or stability of cell surface PON1.     

Cell Adhesion Strength Is Controlled by Intermolecular Spacing of Adhesion Receptors

Spatial patterning of biochemical cues on the micro- and nanometer scale controls numerous cellular processes such as spreading, adhesion, migration, and proliferation. Using force microscopy we show that the lateral spacing of individual integrin receptor-ligand bonds determines the strength of cell adhesion. For spacings ≥90 nm, focal contact formation was inhibited and the detachment forces as well as the stiffness of the cell body were significantly decreased compared to spacings ≤50 nm. Analyzing cell detachment at the subcellular level revealed that rupture forces of focal contacts increase with loading rate as predicted by a theoretical model for adhesion clusters. Furthermore, we show that the weak link between the intra- and extracellular space is at the intracellular side of a focal contact. Our results show that cells can amplify small differences in adhesive cues to large differences in cell adhesion strength.     

Quantitative analysis of cereulide, an emetic toxin of Bacillus cereus, by using rat liver mitochondria

An emetic toxin cereulide, produced by Bacillus cereus, causes emetic food poisonings, but a method for quantitative measurement of cereulide has not been well established. A current detection method is a bioassay method using the HEp-2 cell vacuolation test, but it was unable to measure an accurate concentration. We established a quantitative assay for cereulide based on its mitochondrial respiratory uncoupling activity. The oxygen consumption in a reaction medium containing rat liver mitochondria was rapid in the presence of cereulide. Thus uncoupling effect of cereulide on mitochondrial respiration was similar to those of uncouplers 2,4-dinitrophenol (DNP), carbonylcyanide m-chlorophenylhydrazone (CCCP), and valinomycin. This method gave constant results over a wide range of cereulide concentrations, ranging from 0.05 to 100 microg/ml. The minimum cereulide concentration to detect uncoupled oxygen consumption was 50 ng/ml and increased dose-dependently to the maximum level. Semi-log relationship between the oxygen consumption rate and the cereulide concentration enables this method to quantify cereulide. The results of this method were highly reproducible as compared with the HEp-2 cell vacuolation test and were in good agreement with those of the HEp-2 cell vacuolation test. The enterotoxin of B. cereus or Staphylococcus aureus did not show any effect on the oxygen consumption, indicating this method is specific for the identification of cereulide as a causative agent of emetic food poisonings.     

Liver and intestinal fatty acid binding proteins in control and TGFβ1 gene targeted deficient mice

The effect of transforming growth factor beta-1 (TGF1) expression on fatty acid binding proteins was examined in control and two strains of gene targeted TGF1-deficient mice. Homozygous TGF1-deficient 129 × CF-1, expressing multifocal inflammatory syndrome, had 25% less liver fatty acid binding protein (L-FABP) when compared to control mice. The decrease in L-FABP expression was not due to multifocal inflammatory syndrome since homozygous TGF1-deficient/immunodeficient C3H mice on a SLID background had 36% lower liver L-FABP than controls. This effect was developmentally related and specific to liver, but not the proximal intestine, where L-FABP is also expressed. Finally, the proximal intestine also expresses intestinal-FABP (1-FABP) which decreased 3-fold in the TGF1-deficient/immunodeficient C3H mice only. Thus, TGF1 appears to regulate the expression of L-FABP and I-FABP in the liver and the proximal intestine, respectively.Abbreviations L-FABP liver fatty acid binding protein - I-FABP intestinal fatty acid binding protein - TGF1 transforming growth factor beta-1 - TNF- tumor necrosis factor- - MIP- macrophage inflammatory protein- - PMSF phenylmethyl sulfonyl fluoride - PBS phosphate buffered saline     

Intracellular fate of liposome-encapsulated DNA in mouse liver. Analysis using electron microscope autoradiography and subcellular fractionation

Transient expression of liposome-encapsulated DNA in liver after intravenous injection to rats and mice has raised questions concerning the intracellular fate of this DNA. Electron microscope autoradiography shows that at 10 min after injection the highest concentration of liposomal DNA which is taken up by the liver is associated with lysosomes and vesicles. The proportion of DNA associated with the mitochondria steadily increases for 1 h after injection, up to 48% of the exogenous DNA found in the tissue. Part of this DNA follows the subcellular fractionation profile of the mitochondrial matrix marker, malate dehydrogenase. In contrast, 14% of the liposomal DNA taken up by the liver is found in the nuclei at 3 min after injection, and this percentage decreases over a period of 1 h. These results permit us to establish the distribution of liposome-encapsulated DNA among subcellular organelles in liver at different times after injection.