Fatty Liver and Insulin Resistance in the Liver-Specific Knockout Mice of Mitogen Inducible Gene-6

Mitogen inducible gene-6 (Mig-6) is a feedback inhibitor of epidermal growth factor receptor (EGFR) signaling pathway. The liver-specific knockout mice of the Mig-6 gene (Mig-6d/d) showed hepatomegaly and increased hypercholesterolemia. In this study, the biomarkers of insulin resistance and the effects of high-fat diets in the wild (Mig-6f/f) and Mig-6d/d mice were analyzed. The fasting plasma concentrations of glucose, triglyceride, cholesterols, free fatty acids, and HOMA-IR were measured and the glucose tolerance and insulin resistance tests were performed in the 25-week-old Mig-6f/f and the Mig-6d/d mice. The protein levels of active insulin receptor, glucose 6-phosphatase, and phosphoenolpyruvate carboxykinase were analyzed in the liver and fat. The fasting plasma cholesterol and glucose concentration were higher in the Mig-6d/d mice than the Mig-6f/f mice with increased fat deposition in the liver. But the Mig-6d/d mice had the improved glucose intolerance and insulin resistance without increased amount of phosphoinsulin receptor after insulin infusion in the liver. The hepatic concentration of phosphoenolpyruvate carboxykinase was increased in fasting Mig-6d/d mice. The feeding of high-fat diet accelerated the plasma lipids profiles and HOMA-IR in the Mig-6d/d mice but had no differential effects in oral glucose tolerance test and insulin tolerance test in both genotypes. These results suggest that the activated EGFR signaling might increase the fasting plasma glucose concentration through inducing the hepatic steatosis and the improved whole-body insulin resistance in the KO mice be caused by decreased adipogenesis in fat tissues

Encapsulation and Enhanced Delivery of Topoisomerase I Inhibitors in Functionalized Carbon Nanotubes

The topoisomerase I inhibitors SN-38 and camptothecin (CPT) have shown potent anticancer activity, but water insolubility and metabolic instability limits their clinical application. Utilizing carbon nanotubes as a protective shell for water-insoluble SN-38 and CPT while maintaining compatibility with aqueous media via a carboxylic acid-functionalized surface can thus be a strategy to overcome this limitation. Through hydrophobic–hydrophobic interactions, SN-38 and CPT were successfully encapsulated in carboxylic acid functionalized single-walled carbon nanotubes and dispersed in water. The resulting cell proliferation inhibition and drug distribution profile inside the cells suggest that these drug-encapsulated carbon nanotubes can serve as a promising delivery strategy for water-insoluble anticancer drugs

Amelioration of Hypercholesterolemia by an EGFR Tyrosine Kinase Inhibitor in Mice with Liver-Specific Knockout of <i>Mig-6</i>

<div><p>Mitogen-inducible gene 6 (<i>Mig-6</i>) is a negative feedback inhibitor of epidermal growth factor receptor (EGFR) signaling. We previously found that <i>Mig-6</i> plays a critical role in the regulation of cholesterol homeostasis and in bile acid synthesis. In this study, we investigated the effects of EGFR inhibition to identify a potential new treatment target for hypercholesterolemia. We used a mouse model with conditional ablation of the <i>Mig-6</i> gene in the liver (Alb<i>^cre/+Mig-6^f/f</i>; <i>Mig-6^d/d</i>) to effectively investigate the role of <i>Mig-6</i> in the regulation of liver function. <i>Mig-6^d/d</i> mice were treated with either the EGFR inhibitor gefitinib or statin for 6 weeks after administration of a high-fat or standard diet. We then compared lipid profiles and other parameters among each group of mice. After a high-fat diet, <i>Mig-6^d/d</i> mice showed elevated serum levels of total cholesterol, high-density lipoprotein (HDL) cholesterol, low-density lipoprotein (LDL) cholesterol, triglycerides and glucose, characteristics resembling hypercholesterolemia in diabetic patients. We observed decreases in serum levels of lipids and glucose in high-fat-diet-fed <i>Mig-6^d/d</i> mice after 6 weeks of treatment with gefitinib or statin. Furthermore gefitinib-treated mice showed significantly greater decreases in serum levels of total, HDL and LDL cholesterol compared with statin-treated mice. Taken together, these results suggest that EGFR inhibition is effective for the treatment of hypercholesterolemia in high-fat-diet-fed <i>Mig-6^d/d</i> mice, and our findings provide new insights into the development of possible treatment targets for hypercholesterolemia via modulation of EGFR inhibition.</p></div

Regulation of EGFR expression and Akt signaling by gefitinib.

<p>Western blotting analysis of EGFR, pEGFR, Akt and pAkt levels after gifitinib or statin treatment. ß-actin is included as a lading control.</p

Effects of gefitinib and statin treatments on liver pathology.

<p>Changes in the weight and pathology of the liver after 6 weeks of gefitinib or statin treatment. (A) Weight of the liver. (B) Weight of the liver after body weight adjustment. (C) Hematoxylin-eosin staining. All photomicrographs are ×200 magnification. Values represent the means ±SEM. ^&<i>P</i><0.05 relative to Con, ^#<i>P</i><0.05 relative to G. N-C, normal control; HFD, high-fat diet; Con, control; G, gefitinib; S, statin.</p

Generation of conditional ablation of Mig-6 in the liver and impact of gefitinib on adipose tissue and liver enzymes in <i>Mig-6^d/d</i> mice.

<p>(A) Western blot analysis of Mig-6 in the liver of Mig-6^f/f and Mig-6^d/d mice. Liver tissue from Mig-6^f/f and Mig-6^d/d mice were lysed and equal amounts of protein were subjected to SDS-PAGE and Western blot analysis for Mig-6. (B) Changes of body weight during the course of standard diet or high fat-diet with or without gefitinib or statin. (C) Changes in visceral fat and (D) total fat weight after 6 weeks of gefitinib and statin treatment. (E) Relative changes in plasma alanine aminotransferase and (F) aspartate aminotransferase after 6 weeks of gefitinib and statin treatment. Values represent the means ±SEM. *<i>P</i><0.05 relative to the normal control. N-C, normal control; HFD, high-fat diet; Con, control; G, gefitinib; S, statin.</p

Glucose and insulin tolerance analyses.

<p>Changes in glucose and insulin concentrations after 6 weeks of gefitinib or statin treatment. (A) Fasting glucose concentration. (B) AUC for glucose levels following oral glucose tolerance test. (C) Fasting insulin concentration. (D) The insulin resistance index HOMA-IR. n = 10 each. Values represent the means ±SEM. *<i>P</i><0.05 relative to N-C, ^&<i>P</i><0.05 relative to Con (high-fat diet only group), ^#<i>P</i><0.05 relative to G (gefitinib plus high-fat diet group). N-C, normal control; HFD, high-fat diet; Con, control; G, gefitinib; S, statin.</p