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11 Jun 2015 - Signaling Pathway in Type 2 Diabetes Mellitus Rats. Yunfeng Gao, Mengna Zhang, Tianchen Wu, Mengying Xu, Haonan Cai, and Zesheng ...
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Effects of D-pinitol on insulin resistance through PI3K/ Akt signaling pathway in type 2 diabetes mellitus rats. Yunfeng Gao, Mengna Zhang, Tianchen Wu, Mengying Xu, Haonan Cai, and Zesheng Zhang J. Agric. Food Chem., Just Accepted Manuscript • DOI: 10.1021/acs.jafc.5b01238 • Publication Date (Web): 11 Jun 2015 Downloaded from http://pubs.acs.org on June 18, 2015

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Journal of Agricultural and Food Chemistry is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

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Journal of Agricultural and Food Chemistry

Effects of D-pinitol on insulin resistance through PI3K/Akt signaling pathway in type 2 diabetes mellitus rats

Yunfeng Gao, Mengna Zhang, Tianchen Wu, Mengying Xu, Haonan Cai Zesheng Zhang*

Key Laboratory of Food Nutrition and Safety, Ministry of Education, College of Food Engineering and Biotechnology, Tianjin University of Science & Technolo gy, Tianjin 300457, China

Corresponding Author Tel: (+86) 022 60912431 Fax: (+86) 022 60912431 Email: [email protected] ; [email protected]

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Abstract: D-pinitol, a compound isolated from pinaceae and leguminosae

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plants, has been reported to possess insulin-like properties. Although

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hypoglycemic activity of D-pinitol was recognized in recent years, the molecule

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mechanism of D-pinitol in the treatment of diabetes mellitus remains unclear.

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In this investigation, a model of type 2 diabetes mellitus (T2DM) with insulin

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resistance was established by feeding a high-fat diet (HFD) and injecting

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streptozocin (STZ) to the Sprague Dawley (SD) rats, targeting to explore more

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details of mechanism in the therapy of T2DM. D-pinitol was administrated to

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the diabetic rats as two doses [30, 60 mg/ (kg—bodyweight—d)]. The level of

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fasting blood glucose (FBG) was decreased 12.63% in high-dosage group.

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And the ability of oral glucose tolerance was improved in D-pinitol treated

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groups. The biochemical indexes revealed that D-pinitol had a positive effect

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on hypoglycemic activity. Western boltting suggested that D-pinitol could

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promote the expression of the phosphatidylinositol-3-kinase (PI3K) p85,

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PI3Kp110 as well as the downstream target protein kinase B/Akt (at Ser473).

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Besides, D-pinitol inhibited the expression of glycogen synthesis kinase-3β

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(GSK-3β) protein and regulated the expression of glycogen synthesis (GS)

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protein and then accelerated the glycogen synthesis. From above all, D-pinitol

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played a positive role in regulating insulin mediated glucose uptake in liver

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through translocation and activation of PI3K/Akt signaling pathway in T2DM

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rats.

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Key words: D-pinitol; Diabetes mellitus; PI3K/Akt signaling pathway 2

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Introduction

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Diabetes mellitus is a complex disease which is called “The Silent Killer” due

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to the amount of patients and lots of chronic complications. Around 90% of the

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diabetes cases are T2DM, which is known as non-insulin-dependent diabetes

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mellitus.1 Patients of T2DM mostly are characterized by insulin resistance and

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impaired insulin secretion because of the dysfunction of β-cell caused by the

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high level of blood glucose.2 Irregularly increasing adipose of body tissues

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leads to obesity, raising the risk of insulin resistance and then impairing

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insulin-stimulated glucose uptake in the peripheral tissues.3, 4

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D-pinitol, 3-O-methyl form of D-chiro-inositol, is one of the naturally

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occurring inositol derivatives.5 It is rich in pinaceae plants and has already

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been found in leguminosae plants.6 D-pinitol is regarded as a bioactive

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compound for it can be used for treatments connected with diabetes mellitus

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and its chronic complications. For the most part, many reports have shown the

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favorable effect of D-pinitol on the treatment of disorders associated with

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insulin because of its insulin-like function.7 It is useful in treating diabetes by

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reducing the level of blood glucose in patients with T2DM.8,9,10 And it also

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showed that D-pinitol could stimulate translocation of glucose transporter 4 in

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skeletal muscles of C57BL/5 mice in order to improve insulin sensitivity of the

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diabetic mice.11 However, the molecule mechanism of D-pinitol in the treatment

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of diabetes mellitus, especially on liver, still remains unclear. Liver is the

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predominant visceral organ to regulate the glucose metabolism by means of 3

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plenty of signaling pathways. PI3K/Akt is one of the most primary signaling

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pathways which is believed to be a major mechanism involved in the

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development of insulin resistance.12,

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evaluate the effect of D-pinitol on insulin resistance through PI3K/Akt signaling

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pathway in T2DM rats.

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The aim of this investigation is to

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Materials and Methods

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Materials and chemicals

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D-pinitol (95%) used in this study was purchased from Yipin Biological

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Technology Co., Ltd (Xi’an, China). STZ was purchased from Sigma Chemical

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Co. (St. Louis, MO, USA). Blood glucose meter and blood glucose test strips

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were obtained from Johnson & Johnson, Co. (New Buren Zwick, NJ, USA).

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Rat insulin elisa kit was purchased from Dingguo Changsheng Biotechnology

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Co. Ltd (Beijing, China). Insulin was obtained from Gen-view Scientific INC

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(Tallahassee, FL, USA). Trizol was purchased from TransGen Biotech Co., Ltd.

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(Beijing, China). RIPA, nitrocellulose membrane and SABC (rabbit IgG) – POD

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Kit were brought from Solarbio science & technology Co., Ltd (Beijing, China).

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Antibodies PI3Kp85, PI3Kp110, Akt, phospho-Akt, GSK-3β and GS were

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obtained from Cell Signaling Technology lnc. (Danvers, MA, USA). Secondary

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antibodies were brought from ZSGB-BIO technology Co., Ltd (Beijing, China).

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The other laboratory chemicals were of the analytical grade.

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Animals

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SD rats (200±20 g), purchased from the animal house of Beijing University

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Science Center, were chosen for our experiment. All rats were kept in internal

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flawless animal rooms which were under a controlled environment at 23±2 °C

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with humidity of 55±10%, 12h light/dark cycle and unrestricted food and water.

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The animals were approved by the Animal Care and Use Committee, all the

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related facilities and experimental procedures were executed according to the

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Technical Standards for Testing & Assessment of Health Food (2003).

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Induction of T2DM in rats and medicinal dosage

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All the experimental animals had been acclimatized to the laboratory

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environment for 7 days. Then the animals were randomly divided into normal

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control group (NC) and diabetic control group (DC). NC group, consisting of 20

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rats, was fed with a normal chow diet during the whole study, while the other

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group was fed with HFD. After a month, the HFD rats were injected

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intraperitoneally with STZ solution at a dose of 30 mg / (kg—b.w.). The STZ was

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dissolved in citrate buffer at the pH of 4.2-4.5. The rats in NC group were

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injected with the citrate buffer vehicle. 72h after injection, the rats in DC group

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with blood glucose level ≥ 11.1mmol/L were considered as T2DM rats and

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would be used in future experiments. These T2DM rats were fed with HFD

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throughout the whole study. Then the T2DM rats were randomly divided into

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three groups with 10 animals each. The first group (low-dosage group, LD)

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received D-pinitol at 30 mg / (kg—b.w.) per day, the second group (high-dosage

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group, HD) received D-pinitol at 60 mg / (kg—b.w.) per day and the last one

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received distilled water only (diabetes control group, DC). 10 rats were chosen

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from the normal control group to receive D-pinitol at 60 mg / (kg—b.w.) per day

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as the normal high-dosage control group (NH).

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Oral glucose tolerance test (OGTT) and insulin tolerance test (ITT)

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OGTT was performed in overnight fasted rats from every group. Vehicle

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(distilled water) was orally administered to NC and DC groups. 30 mg/kg, 60

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mg/kg and 60 mg/kg D-pinitol were orally administered to LD, HD and NH

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groups. 20 min later, all the rats were orally administrated glucose with a dose

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of 2g/kg. Blood was withdrawn from the tip of the tail at 0, 30, 60 and 120 min

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from all 5 groups to measure the blood glucose level.

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ITT were performed in overnight fasted rats from all groups 3 days after the

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OGTT. 20 min after administered the vehicle (distilled water) and D-pinitol, the

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rats were injected insulin intraperitoneally with a dose of 0.15 U/kg. The same

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as OGTT had shown that the blood samples were withdrawn at 0, 30, 60 and

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120 min after injected insulin, and the blood glucose level was measured.

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Biochemical analysis

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FBG level was determined by the blood glucose meter and test strips each

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week. The fasting serum insulin (FINS) was determined by ELISA kit. The

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insulin sensitivity index (ISI) was calculated following the formula ISI = Ln

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(1/FINS*FBG). And the Homeostasis model assessment-β (HOMA-β) were

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calculated following the formula HOMA-β = (20*FINS) / (FBG-3.5). All the

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parameters were performed according to the manufactures’ instructions. The

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blood samples and viscera organs were stored at -80°C in the refrigerator for

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future research.

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Real-time polymerase chain reaction (RT-PCR) analysis

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RT-PCR was operated to determine the expression levels of the genes.

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Total RNA was extracted from liver using Trizol reagent, and the concentration

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of the total RNA was determined by the ultraviolet spectrophotometer. It was

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converted to DNA by RT-PCR kit and the reaction was performed according to

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the manufacturer’s instructions. The specific primers which include both sense

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and anti-sense were used for the amplification of DNA (Table1).

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Western blot analysis

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The expression of protein including PI3Kp85 (85kDa), PI3Kp110 (110 kDa),

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Akt (60kDa), p-Akt (60kDa), GSK-3β (46kDa) and GS (81-85kDa) were

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analyzed by western blot. In brief, 100mg liver was homogenized in RIPA

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buffer for 10 min, followed by centrifugation at 10,000 rpm for 5 min at 4°C. The

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supernatant was transferred to a new clean centrifuge tube, and Bradford

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colorimetric method was used to determine the concentration of the total

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protein. The tissue protein (50-70 µg) was subjected to 10% SDS-PAGE for

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0.5h at 80V and 2.5h at 100V, in order to separate the aim protein from the

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others. Proteins were transferred to a nitrocellulose membrane for 3h at 300

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mA by wet transfer equipment. The membrane was incubated in blocking

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solution containing 5% non-fat dried milk for 2h at room temperature.

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Subsequently, the membrane was exposed to desire the primary antibodies,

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PBS containing PI3Kp85 antibody (1:1000), PI3Kp110 antibody (1:1000), Akt

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antibody (1:1000), p-Akt (Ser473) antibody (1:2000), GSK-3β (1:1000)and

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GS (1:1000) were incubated to the membrane at 4°C overnight and β-actin (43 8

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kDa) was used as control protein. After incubated with the secondary antibody

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for 2h at room temperature, the membrane was exposed to chemiluminescent

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reagent (ECL) for about 5-10 min. The expressions of the proteins on the

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membranes with fluorescence were exposed to the X-ray photographic films in

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the darkroom and the band densities were quantified.

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Immunohistochemistry

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Liver tissues embedded in paraffin were performed on 5-µm paraffin

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sections for immunohistochemical staining. The paraffin sections were

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dewaxed and rehydrated before dipped into 0.01M citrate buffer (pH 6.0) with

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a boiling water reaction in order to retrieve antigen. The paraffin sections were

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incubated with 3% H2O2 in order to quench the activity of endogenous

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peroxidase. And then the sections were incubated in the solution containing 3%

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BSA to block non-specific binding sites, while endogenous avidin-binding

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activity was inhibited by continuously treated with avidin-biotin. And the

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following steps of the immunodetection experiment were operated according to

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the manufactures’ instruction of SABC (rabbit IgG) – POD Kit. For each

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antibody, a negative control was included in which the primary antibody was

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replaced with phosphate buffer saline (PBS).

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Statistical analysis

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All the data were presented as means ± S.D. T-test was used to exhibit the

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significance of differences between samples. These differences were

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considered significant when p