Seng-Wong Huang

Insulin Up-Regulates Heme Oxygenase-1 Expression in 3T3-L1 Adipocytes via PI3-Kinase- and PKC-Dependent Pathways and Heme Oxygenase-1–Associated MicroRNA Downregulation

Heme oxygenase-1 (HO-1), the rate-limiting enzyme in heme catabolism, has antioxidant, antiinflammatory, and antiapoptotic effects in many physiological systems. HO-1 activity in obese mice is lower than in controls, and a sustained increase in HO-1 protein levels ameliorates insulin resistance and compensatory hyperinsulinemia. In the present study, we explored the regulatory effect of insulin on HO-1 expression in 3T3-L1 adipocytes and the underlying mechanism. We investigated the time- and dose-effect of insulin on HO-1 expression in 3T3-L1 adipocytes. Using specific inhibitors acting on insulin signaling pathways, we clarified the involvement of insulin downstream signaling molecules in insulin-regulated HO-1 expression. We also investigated the involvement of microRNAs (miRNAs) in insulin-regulated HO-1 expression using microarray and real-time RT-PCR assays. In an in vivo study, we performed insulin/glucose coinfusion in rats to increase circulating insulin levels for 8 h, then measured adipocyte HO-1 expression. Insulin caused a significant increase in HO-1 expression that was time- and dose-dependent, and this effect was blocked by inhibition of phosphatidylinositol 3 (PI3)-kinase activation using LY294002 (50 μM) or of protein kinase C activation using Ro-318220 (2 μM), but not by an Akt inhibitor, triciribine (10 μM). Furthermore, incubation of 3T3-L1 adipocytes with 100 nm insulin resulted in a significant decrease in levels of the miRNAs mir-155, mir-183, and mir-872, and this effect was also blocked by pretreatment with LY294002 or Ro-318220, but not triciribine. An in vivo study in rats showed that 8 h of a hyperinsulinemic euglycemic state resulted in a significant increase in adipocyte HO-1 expression. In conclusion, insulin increases HO-1 protein expression in 3T3-L1 adipocytes via PI3-kinase and protein kinase C-dependent pathways and miRNAs down-regulation.

Lack of detrimental effects of nitric oxide inhibition in bile duct-ligated rats with hepatic encephalopathy.

Background  The pathogenetic mechanisms of hepatic encephalopathy (HE) are not fully understood. Vasodilatation induced by nitric oxide (NO) may be involved in the development of HE. There is no comprehensive data concerning the effects of NO inhibition on HE in chronic liver disease.

Effect of Endothelin-1 on Lipolysis in Rat Adipocytes

Objective: To explore the role of endothelin‐1 (ET‐1) on lipid metabolism, we examined the effect of ET‐1 on lipolysis in rat adipocytes.

Lack of detrimental or therapeutic effects of cyclooxygenase inhibition in bile duct-ligated rats with hepatic encephalopathy

Background:  The pathogenetic mechanisms of hepatic encephalopathy (HE) are not fully understood. Cerebral blood flow regulated by cyclooxygenase (COX) may be involved in the development of HE. There are no comprehensive data concerning the effects of COX inhibition on HE in chronic liver disease.

Human chorionic gonadotropin regulates gastric emptying in ovariectomized rats

Prolongation of gastrointestinal transit resulting in nausea and vomiting in pregnancy (NVP) is the most common phenomenon during the first trimester of pregnancy. Increased human chorionic gonadotropin (hCG) concentration during the first trimester is the most likely cause of NVP. The aim of this study was to investigate the effect of hCG on gastrointestinal transit and plasma concentrations of cholecystokinin (CCK) in ovariectomized (Ovx) rats. I.p. injection of hCG was used to evaluate the dose effect of hCG on gastrointestinal transit in Ovx rats. The CCK antagonist lorglumide was used to clarify the role of CCK in regulating gastrointestinal transit. Gastrointestinal transit was assessed 15 min after intragastric gavage of a mixture of 10% charcoal and Na(2)(51)CrO(4) (0.5 μCi/ml). After i.p. administration of hCG, gastric emptying was inhibited in Ovx rats, but intestinal transit was not affected. Plasma CCK concentrations were increased in a dose-dependent manner after hCG treatment, and gastric emptying showed a significant negative correlation with CCK concentrations (P=0.01, r(2)=-0.5104). Peripheral administration (i.p.) of lorglumide, a selective CCK(1) receptor antagonist, attenuated the hCG-induced inhibition of gastric emptying in Ovx rats, whereas central administration via the i.c.v. route did not. hCG treatment of Ovx rats inhibits gastric emptying in a dose-dependent manner via a peripheral mechanism of CCK hypersecretion and activation of CCK(1) receptors.

Losartan ameliorates renal injury, hypertension, and adipocytokine imbalance in 5/6 nephrectomized rats.

The mechanisms underlying insulin sensitivity and fat tissue distribution in chronic renal insufficiency remain unclear. Previous studies have shown the benefits of angiotensin II receptor blockers on moderately nourished to well-nourished patients with the metabolic syndrome. The current study explored the effect of losartan, the first selective angiotensin II receptor blocker, on insulin sensitivity and visceral fat tissue distribution in a 5/6 nephrectomized (N) rat model and investigated the expression of adipose tissue adipocytokines. Male Sprague-Dawley rats (200 g to 250 g) were subjected to 5/6 nephrectomy, and the adipocytes isolated from the visceral fat tissues were then studied. Results showed that desmin expression was significantly suppressed and systolic blood pressure was successfully normalized in the losartan-administered (NA) group. The weight of the visceral fat pad remarkably decreased in the N and NA groups (100 mg/500 ml drinking water) compared with the control group. The weight did not decrease further in the NA group compared with the N group. Insulin resistance was more remarkable in the N group compared with the control and NA groups. Moreover, the adipose tissue expression of adiponectin and leptin was downregulated whereas that of resistin was upregulated in the N group compared with the control group. However, the adiponectin, leptin, and resistin adipose tissue expression returned to their basal values in the NA group. These findings indicated that losartan administration ameliorated renal injury, systolic blood pressure, and adipocytokine imbalance of the adipose tissue in chronic renal insufficiency. Insulin sensitivity was not improved.

Adipocytes play an etiological role in the podocytopathy of high-fat diet-fed rats

Obesity is a risk factor that promotes progressive kidney disease. Studies have shown that an adipocytokine imbalance contributes to impaired renal function in humans and animals, but the underlying interplay between adipocytokines and renal injury remains to be elucidated. We aimed to investigate the mechanisms linking obesity to chronic kidney disease. We assessed renal function in high-fat (HF) diet-fed and normal diet-fed rats, and the effects of preadipocyte- and adipocyte-conditioned medium on cultured podocytes. HF diet-fed and normal diet-fed Sprague Dawley rats were used to analyze the changes in plasma BUN, creatinine, urine protein and renal histology. Additionally, podocytes were incubated with preadipocyte- or adipocyte-conditioned medium to investigate the effects on podocyte morphology and protein expression. In the HF diet group, 24 h urinary protein excretion (357.5 ± 64.2 mg/day vs 115.9 ± 12.4 mg/day, P < 0.05) and the urine protein/creatinine ratio were significantly higher (1.76 ± 0.22 vs 1.09 ± 0.15, P < 0.05), increased kidney weight (3.54 ± 0.04 g vs 3.38 ± 0.04 g, P < 0.05) and the glomerular volume and podocyte effacement increased by electron microscopy. Increased renal expression of desmin and decreased renal expression of CD2AP and nephrin were also seen in the HF diet group (P < 0.05). Furthermore, we found that adipocyte-conditioned medium-treated podocytes showed increased desmin expression and decreased CD2AP and nephrin expression compared with that in preadipocyte-conditioned medium-treated controls (P < 0.05). These findings show that adipocyte-derived factor(s) can modulate renal function. Adipocyte-derived factors play an important role in obesity-related podocytopathy.

The use of dehydroepiandrosterone-treated rats is not a good animal model for the study of metabolic abnormalities in polycystic ovary syndrome

OBJECTIVE Hyperandrogenism is the hallmark of polycystic ovary syndrome (PCOS). The use of dehydroepiandrosterone (DHEA)-treated rats is thought to be a suitable animal model to study PCOS. In the present study, we assessed the severity of reproductive and metabolic abnormalities in DHEA-treated rats. MATERIAL AND METHODS Immature female Sprague-Dawley rats were divided into control and DHEA-treated groups. Reproductive parameters including estrus cycle and sex hormones were measured after sexual maturity. Adiposity, insulin sensitivity, and plasma lipid profiles were analyzed to assess metabolic profiles. After sacrifice, the insulin signaling pathway and lipogenic genes were analyzed by immunoblotting and polymerase chain reaction, respectively. RESULTS An abnormal estrus cycle was observed in the DHEA-treated rats. DHEA treatment also increased plasma testosterone levels and caused multiple cystic follicle formation, which is compatible with the definition of PCOS. There were no significant changes in fasting glucose, fasting insulin, plasma lipid profiles, and blood pressure levels. The adiposity of the DHEA-treated rats was also lower than in the control rats. Moreover, glucose tolerance and insulin sensitivity were only mildly impaired in the DHEA-treated rats after oral glucose tolerance and insulin tolerance tests, even though insulin signaling in skeletal muscles was decreased in the DHEA-treated group. CONCLUSION DHEA-treated rats had reproductive abnormalities which mimicked symptoms of human PCOS. In metabolic parameters, DHEA treatment did not show insulin resistance in the female rats, suggesting that the use of DHEA-treated rats is not a good animal model for the study of metabolic abnormalities in PCOS.