Pathophysiological mechanisms involved in non-alcoholic steatohepatitis and novel potential therapeutic targets

Non-alcoholic fatty liver disease (NAFLD) is a major health care problem and represents the hepatic expression of the metabolic syndrome. NAFLD is classified as non-alcoholic fatty liver (NAFL) or simple steatosis, and non-alcoholic steatohepatitis (NASH). NASH is characterized by the presence of steatosis and inflammation with or without fibrosis. The physiopathology of NAFL and NASH and their progression to cirrhosis involve several parallel and interrelated mechanisms, such as, insulin resistance (IR), lipotoxicity, inflammation, oxidative stress, and recently the gut-liver axis interaction has been described. Incretin-based therapies could play a role in the treatment of NAFLD. Glucagon-like peptide-1 (GLP-1) is an intestinal mucosa-derived hormone which is secreted into the bloodstream in response to nutrient ingestion; it favors glucose-stimulated insulin secretion, inhibition of postprandial glucagon secretion and delayed gastric emptying. It also promotes weight loss and is involved in lipid metabolism. Once secreted, GLP-1 is quickly degraded by dipeptidyl peptidase-4 (DPP-4). Therefore, DPP-4 inhibitors are able to extend the activity of GLP-1. Currently, GLP-1 agonists and DPP-4 inhibitors represent attractive options for the treatment of NAFLD and NASH. The modulation of lipid and glucose metabolism through nuclear receptors, such as the farsenoid X receptor, also constitutes an attractive therapeutic target. Obeticholic acid is a potent activator of the farnesoid X nuclear receptor and reduces liver fat content and fibrosis in animal models. Ursodeoxycholic acid (UDCA) is a hydrophilic bile acid with immunomodulatory, anti-inflammatory, antiapoptotic, antioxidant and anti-fibrotic properties. UDCA can improve IR and modulate lipid metabolism through its interaction with nuclear receptors such as, TGR5, farnesoid X receptor-α, or the small heterodimeric partner. Finally, pharmacologic modulation of the gut microbiota could have a role in the therapy of NAFLD and NASH. Probiotics prevent bacterial translocation and epithelial invasion, inhibit mucosal adherence by bacteria, and stimulate host immunity. In animal models, probiotics prevent obesity, decrease transaminase levels, and improve IR and liver histology in NASH.     

糖尿病性认知功能障碍:一个不容忽视的问题

糖尿病对脑部结构功能有多方面影响,但糖尿病引发的认知功能障碍却常常被忽视.糖尿病性认知功能障碍的发生机制十分复杂,其中糖脂毒性、胰岛素抵抗、低血糖及Ca2+稳态被破坏等可能起要作用.除糖尿病常规治疗方案外,糖尿病性认知功能障碍尚需要探索更加有效的治疗措施.     

Lipidomics in non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD), the most common chronic liver disorder in Western countries, comprises steatosis to nonalcoholic steatohepatitis (NASH), with the latter having the potential to progress to cirrhosis. The transition from isolated steatosis to NASH is still poorly understood, but lipidomics approach revealed that the hepatic lipidome is extensively altered in the setting of steatosis and steatohepatitis and these alterations correlate with disease progression. Recent data suggest that both quantity and quality of the accumulated lipids are involved in pathogenesis of NAFLD. Changes in glycerophospholipid, sphingolipid, and fatty acid composition have been described in both liver biopsies and plasma of patients with NAFLD, implicating that specific lipid species are involved in oxidative stress, inflammation, and cell death. In this article, we summarize the findings of main human lipidomics studies in NAFLD and delineate the currently available information on the pathogenetic role of each lipid class in lipotoxicity and disease progression.     

高浓度葡萄糖、脂肪酸和糖皮质激素对PDX-1表达和胰岛素分泌功能的影响

SD大鼠胰岛细胞分别在含5.6mmol／L葡萄糖、33mmol／L葡萄糖、0．6mmol／L软脂酸或20nmol／L地塞米松培养液中培养3d，RIA测定基础和葡萄糖刺激后胰岛素分泌量，免疫组化法测定细胞内胰十二指肠同源盒蛋白1（PDX-1）蛋白表达和原位杂交法测定细胞内PDX-1 mRNA表达。结果显示高浓度葡萄糖、脂肪酸和糖皮质激素对PDX-1蛋白表达和胰岛素分泌均有抑制作用。     

京尼平抑制饱和脂肪酸诱导的HepG2细胞凋亡和内质网应激

目的 探讨京尼平减轻棕榈酸对HepG2细胞毒性的作用及机制.方法 将HepG2细胞分为4组,分别用牛血清白蛋白、棕榈酸(1 mmol/L)、京尼平(20 μmol/L)或京尼平(20 μmol/L)预处理30 min后棕榈酸(1 mmol/L)孵育24 h,检测细胞活力及乳酸脱氧酶(LDH)释放;孵育16 h后经流式细...     

Lipotoxicity in the liver

Obesity due to excessive food intake and the lack of physical activity is becoming one of the most serious public health problems of the 21^st century. With the increasing prevalence of obesity, non-alcoholic fatty liver disease is also emerging as a pandemic. While previously this pathophysiological condition was mainly attributed to triglyceride accumulation in hepatocytes, recent data show that the development of oxidative stress, lipid peroxidation, cell death, inflammation and fibrosis are mostly due to accumulation of fatty acids, and the altered composition of membrane phospholipids. In fact, triglyceride accumulation might play a protective role, and the higher toxicity of saturated or trans fatty acids seems to be the consequence of a blockade in triglyceride synthesis. Increased membrane saturation can profoundly disturb cellular homeostasis by impairing the function of membrane receptors, channels and transporters. However, it also induces endoplasmic reticulum stress via novel sensing mechanisms of the organelle’s stress receptors. The triggered signaling pathways in turn largely contribute to the development of insulin resistance and apoptosis. These findings have substantiated the lipotoxic liver injury hypothesis for the pathomechanism of hepatosteatosis. This minireview focuses on the metabolic and redox aspects of lipotoxicity and lipoapoptosis, with special regards on the involvement of endoplasmic reticulum stress responses.     

The growth hormone-insulin like growth factor axis revisited: lessons from IGF-1 and IGF-1 receptor gene targeting

We have created a liver-specific igf1 gene-deletion mouse model (LID) with markedly reduced circulating IGF-I levels. They demonstrate that while they have normal growth and development they develop insulin resistance secondary to the elevation of circulating growth hormone. When mated with an acid-labile subunit (ALS) gene-deleted mouse they also show osteopenia suggesting that circulating IGF-I levels play a significant role in bone formation. In a separate transgenic mouse we created a model of severe insulin resistance and type 2 diabetes by the overexpression of a dominant-negative IGF-I receptor in skeletal muscle. In this model we show that lipotoxicity plays a major role in the progression of the disease and is affected by treatment with a fibrate, which reverses the insulin resistance and diabetic state. These models are therefore very useful in studying human physiology and disease states.This work was presented in part at the IPNA Seventh Symposium on Growth and Development in Children with Chronic Kidney Disease: The Molecular Basis of Skeletal Growth, 1–3 April 2004, Heidelberg, Germany     

Mechanisms of insulin resistance caused by nutrient toxicity.

Insulin resistance, the impaired action of insulin, has been linked to many important consequences, including Type 2 diabetes, hypertension, dyslipidemia, acanthosis nigricans and polycystic ovarian syndrome. Although there are some genetic causes for insulin resistance, the most common cause is an excess of nutrition a condition called "Nutrient Toxicity". Both excess glucose and excess fat can cause insulin resistance in muscle and fat tissues and excess fat can cause insulin resistance in the liver. High fat feeding and fat infusion rapidly lead to the development of insulin resistance caused by impairment in glucose transport. Other studies have shown defects in insulin signaling possibly secondary to activation of Protein Kinase C resulting from the accumulation of active fatty acyl CoA's. Glucose toxicity has been studied both in vivo and in vitro. In vivo it has been shown that rats over-expressing the gluconeogenic enzyme Phosphoenol Pyruvate Carboxykinase (PEPCK) develop insulin resistance in fat and muscle tissues and some features of the metabolic syndrome including mild obesity and dyslipidemia. Excess glucose entry in fat cells results in increased flux through the hexosamine biosynthesis pathway leading to activation of protein kinase C and impairment of glucose transport. Obesity resulting from excess nutrient intake can also cause insulin resistance by an increase in the production of agents that impair insulin action such as TNFalpha and resistin and a decrease in the production of an insulin sensitizing compound adiponectin. Both glucose and free fatty acids acutely stimulate insulin secretion but chronic exposure to high levels of either nutrient leads to impairment of beta cell function. The combination of insulin resistance and beta cell failure leads to diabetes. Nutrient toxicity is thus the driving cause of the diabetes epidemic that is being recorded around the world.     

肥胖型2型糖尿病OLETF鼠胰岛β细胞凋亡在发病中的意义

目的　了解肥胖型 2型糖尿病 OL ETF鼠胰岛β细胞是否存在凋亡及β细胞凋亡与糖尿病发生发展的关系。　方法　 OL ETF及对照鼠 L ETO各 2 0只 ,胰腺切片用 HE染色和 TU NEL方法观察胰岛β细胞凋亡的情况。　结果　 (1) OL ETF鼠糖尿病发病率为 95 % ,L ETO未发生糖尿病。 (2 )仅在 OL ETF鼠胰腺切片中观察到凋亡的β细胞数目增高的现象。 (3)各周龄 OL ETF鼠胰岛β细胞凋亡的百分数明显高于 L ETO鼠 (P=1.2 6× 10 - 1 7)。 (4) OL ETF鼠胰岛β细胞凋亡的百分数在糖尿病发病后 4周较糖尿病发病前增高。　结论　 OL ETF鼠胰岛β细胞在糖尿病发病前存在高水平的凋亡 ,糖尿病发病后进一步增高