Compound K attenuates glucose intolerance and hepatic steatosis through AMPK-dependent pathways in type 2 diabetic OLETF rats

BACKGROUND/AIMS: Non-alcoholic fatty liver disease is associated with insulin resistance. Compound K (CK) is the final metabolite of panaxadiol ginsenosides that have been shown to exert antidiabetic effects. However, the molecular mechanism of the antidiabetic effects in the liver have not been elucidated; further, whether CK has beneficial effects in hepatosteatosis remains unclear. Therefore, we evaluated the effect of CK on hepatosteatosis as well as its mechanism in high-fat diet (HFD)-fed type 2 diabetic Otsuka Long-Evans Tokushima Fatty (OLETF) rats. METHODS: Twenty-four-week-old male OLETF rats were assigned to four groups: control (saline), CK 10 mg/kg, CK 25 mg/kg, or metformin 300 mg/kg (positive control); all treatments were administered orally for 12 weeks. RESULTS: Fasting glucose levels of the CK25 group were significantly lower than those of the control group during the 12 weeks. The results of the oral glucose tolerance test showed that both the glucose concentration after glucose loading and the fasting insulin levels of the CK25 group were significantly lower than those of the control. Hepatosteatosis was significantly improved by CK25. CK25 and metformin significantly increased the phosphorylation of hepatic adenosine monophosphate-activated protein kinase (AMPK). CK25 significantly inhibited the expression of sterol regulatory element-binding protein-1c and fatty acid synthase, while upregulating that of peroxisome proliferator-activated receptor-α and carnitine palmitoyltransferase-1. CONCLUSIONS: CK improved glucose intolerance and hepatosteatosis in HFD-fed OLETF rats through AMPK activation, which has dual mode of action that involves decreasing the synthesis of fatty acids and increasing fatty acid oxidation.

Beneficial Effects of Aerobic Exercise Training Combined with Rosiglitazone on Glucose Metabolism in Otsuka Long Evans Tokushima Fatty Rats

BACKGROUND: Regular aerobic exercise is essential for the prevention and management of type 2 diabetes mellitus and may be particularly beneficial for those treated with thiazolidinediones, since it may prevent associated weight gain. This study aimed to evaluate the effect of combined exercise and rosiglitazone treatment on body composition and glucose metabolism in obese diabetes-prone animals. METHODS: We analyzed metabolic parameters, body composition, and islet profiles in Otsuka Long Evans Tokushima Fatty rats after 28 weeks of aerobic exercise, rosiglitazone treatment, and combined exercise and rosiglitazone treatment. RESULTS: Combined exercise with rosiglitazone showed significantly less increase in weight and epididymal fat compared to rosiglitazone treatment. Aerobic exercise alone and combined rosiglitazone and exercise treatment led to similar retention of lean body mass. All experimental groups showed a decrease in fasting glucose. However, the combined exercise and rosiglitazone therapy group showed prominent improvement in glucose tolerance compared to the other groups. Rescue of islet destruction was observed in all experimental groups, but was most prominent in the combined therapy group. CONCLUSION: Regular aerobic exercise combined with rosiglitazone treatment can compensate for the adverse effect of rosiglitazone treatment and has benefit for islet preservation.

The Effects of High Fat Diet and Resveratrol on Mitochondrial Activity of Brown Adipocytes

BACKGROUND: Resveratrol (RSV) is a polyphenolic phytoalexin that has many effects on metabolic diseases such as diabetes and obesity. Given the importance of brown adipose tissue (BAT) for energy expenditure, we investigated the effects of RSV on brown adipocytes. METHODS: For the in vitro study, interscapular BAT was isolated from 7-week-old male Sprague Dawley rats. For the in vivo study, 7-week-old male Otsuka Long Evans Tokushima Fatty (OLETF) rats were divided into four groups and treated for 27 weeks with: standard diet (SD); SD+RSV (10 mg/kg body weight, daily); high fat diet (HFD); HFD+RSV. RSV was provided via oral gavage once daily during the in vivo experiments. RESULTS: RSV treatment of primary cultured brown preadipocytes promoted mitochondrial activity, along with over-expression of estrogen receptor α (ER-α). In OLETF rats, both HFD and RSV treatment increased the weight of BAT and the differentiation of BAT. However, only RSV increased the mitochondrial activity and ER-α expression of BAT in the HFD-fed group. Finally, RSV improved the insulin sensitivity of OLETF rats by increasing the mitochondrial activity of BAT, despite having no effects on white adipocytes and muscles in either diet group. CONCLUSION: RSV could improve insulin resistance, which might be associated with mitochondrial activity of brown adipocyte. Further studies evaluating the activity of RSV for both the differentiation and mitochondrial activity of BAT could be helpful in investigating the effects of RSV on metabolic parameters.

Anti-Proliferative Effects of Rutin on OLETF Rat Vascular Smooth Muscle Cells Stimulated by Glucose Variability

PURPOSE: Proliferation of vascular smooth muscle cells (VSMCs) plays a crucial role in atherosclerosis. Rutin is a major representative of the flavonol subclass of flavonoids and has various pharmacological activities. Currently, data are lacking regarding its effects on VSMC proliferation induced by intermittent hyperglycemia. Here, we demonstrate the effects of rutin on VSMC proliferation and migration according to fluctuating glucose levels. MATERIALS AND METHODS: Primary cultures of male Otsuka Long-Evans Tokushima Fatty (OLETF) rat VSMCs were obtained from enzymatically dissociated rat thoracic aortas. VSMCs were incubated for 72 h with alternating normal (5.5 mmol/L) and high (25.0 mmol/L) glucose media every 12 h. Proliferation and migration of VSMCs, the proliferative molecular pathway [including p44/42 mitogen-activated protein kinases (MAPK), mitogen-activated protein kinase kinase 1/2 (MEK1/2), p38 MAPK, phosphoinositide 3-kinase (PI3K), c-Jun N-terminal protein kinase (JNK), nuclear factor kappa B (NF-kappaB), and Akt], the migratory pathway (big MAPK 1, BMK1), reactive oxygen species (ROS), and apoptotic pathway were analyzed. RESULTS: We found enhanced proliferation and migration of VSMCs when cells were incubated in intermittent high glucose conditions, compared to normal glucose. These effects were lowered upon rutin treatment. Intermittent treatment with high glucose for 72 h increased the expression of phospho-p44/42 MAPK (extracellular signal regulated kinase 1/2, ERK1/2), phospho-MEK1/2, phospho-PI3K, phospho-NF-kappaB, phospho-BMK1, and ROS, compared to treatment with normal glucose. These effects were suppressed by rutin. Phospho-p38 MAPK, phospho-Akt, JNK, and apoptotic pathways [B-cell lymphoma (Bcl)-xL, Bcl-2, phospho-Bad, and caspase-3] were not affected by fluctuations in glucose levels. CONCLUSION: Fluctuating glucose levels increased proliferation and migration of OLETF rat VSMCs via MAPK (ERK1/2), BMK1, PI3K, and NF-kappaB pathways. These effects were inhibited by the antioxidant rutin.

Femoral bone structure in Otsuka Long-Evans Tokushima Fatty rats

OBJECTIVES: Type 2 diabetes mellitus (T2DM) increases fracture risk despite normal to high levels of bone mineral density. Bone quality is known to affect bone fragility in T2DM. The aim of this study was to clarify the trabecular bone microstructure and cortical bone geometry of the femur in T2DM model rats. METHODS: Five-week-old Otsuka Long-Evans Tokushima Fatty (OLETF; n = 5) and Long-Evans Tokushima Otsuka (LETO; n = 5) rats were used. At the age of 18 months, femurs were scanned with micro-computed tomography, and trabecular bone microstructure and cortical bone geometry were analyzed. RESULTS: Trabecular bone microstructure and cortical bone geometry deteriorated in the femur in OLETF rats. Compared with in LETO rats, in OLETF rats, bone volume fraction, trabecular number and connectivity density decreased, and trabecular space significantly increased. Moreover, in OLETF rats, cortical bone volume and section area decreased, and medullary volume significantly increased. CONCLUSIONS: Long-term T2DM leaded to deterioration in trabecular and cortical bone structure. Therefore, OLETF rats may serve as a useful animal model for investigating the relationship between T2DM and bone quality.

Protective Effects of Curcumin on Renal Oxidative Stress and Lipid Metabolism in a Rat Model of Type 2 Diabetic Nephropathy

PURPOSE: Diabetic nephropathy is a serious complication of type 2 diabetes mellitus, and delaying the development of diabetic nephropathy in patients with diabetes mellitus is very important. In this study, we investigated inflammation, oxidative stress, and lipid metabolism to assess whether curcumin ameliorates diabetic nephropathy. MATERIALS AND METHODS: Animals were divided into three groups: Long-Evans-Tokushima-Otsuka rats for normal controls, Otsuka-Long-Evans-Tokushima Fatty (OLETF) rats for the diabetic group, and curcumin-treated (100 mg/kg/day) OLETF rats. We measured body and epididymal fat weights, and examined plasma glucose, adiponectin, and lipid profiles at 45 weeks. To confirm renal damage, we measured albumin-creatinine ratio, superoxide dismutase (SOD), and malondialdehyde (MDA) in urine samples. Glomerular basement membrane thickness and slit pore density were evaluated in the renal cortex tissue of rats. Furthermore, we conducted adenosine monophosphate-activated protein kinase (AMPK) signaling and oxidative stress-related nuclear factor (erythroid-derived 2)-like 2 (Nrf2) signaling to investigate mechanisms of lipotoxicity in kidneys. RESULTS: Curcumin ameliorated albuminuria, pathophysiologic changes on the glomerulus, urinary MDA, and urinary SOD related with elevated Nrf2 signaling, as well as serum lipid-related index and ectopic lipid accumulation through activation of AMPK signaling. CONCLUSION: Collectively, these findings indicate that curcumin exerts renoprotective effects by inhibiting renal lipid accumulation and oxidative stress through AMPK and Nrf2 signaling pathway.

Effects of Moderate Alcohol Intake in the Bladder of the Otsuka Long Evans Tokushima Fatty Diabetic Rats

Diabetes is related with a number of cystopathic complications. However, there have been no studies about the influence of alcohol consumption in the bladder of type 2 diabetes. Thus, we investigated the effect of moderate alcohol intake in the bladder of the Otsuka Long Evans Tokushima Fatty (OLETF) diabetic rat. The non-diabetic Long-Evans Tokushima Otsuka (LETO, n=14) and the OLETF control group (n=14) were fed an isocaloric diet; the LETO (n=14) and the OLETF ethanol group (n=14) were fed 36% ethanol 7 g/kg/day. After ten weeks, muscarinic receptors, RhoGEFs, myogenic change, and the level of oxidative stress were evaluated. Moderate alcohol intake significantly decreased excessive muscarinic receptor and Rho kinase expressions in the OLETF rats compared with the LETO rats. In addition, iNOS and collagen expression were not changed in the OLETF rats in spite of alcohol consumption. Superoxide dismutase levels, which is involved in antioxidant defense, in the LETO rats were significantly decreased after alcohol consumption, however those in the OLETF rats were similar. Moderate alcohol consumption reduces the oxidative stress, and may prevent molecular and pathologic changes of the bladder of rats with type 2 diabetes.

All-Trans Retinoic Acid Has a Potential Therapeutic Role for Diabetic Nephropathy

PURPOSE: The aim of this study was to examine the effects of all-trans retinoic acid (ATRA) on diabetic nephropathy. MATERIALS AND METHODS: We measured amounts of urinary albumin excretion (UAE) after administrating ATRA to Otsuka Long-Evans Tokushima Fatty (OLETF) rats. In order to understand the mechanism of action for ATRA, we administrated ATRA to examine its inhibitory action on the production of transforming growth factor-beta1 (TGF-beta1), protein kinase C (PKC), and reactive oxidative stress (ROS) in cultured rat mesangial cells (RMCs). RESULTS: After 16 weeks of treatment, UAE was lower in the ATRA-treated OLETF rats than in the non-treated OLETF rats (0.07+/-0.03 mg/mgCr vs. 0.17+/-0.15 mg/mgCr, p<0.01). After incubation of RMCs in media containing 30 or 5 mM of glucose, treatment with ATRA showed time- and dose-dependent decreases in TGF-beta1 levels and ROS. Moreover, ATRA treatment showed a dose-dependent decrease in PKC expression. CONCLUSION: ATRA treatment suppressed UAE and TGF-beta1 synthesis, which was mediated by significant reductions in PKC activity and ROS production. Our results suggest that ATRA has a potential therapeutic role for diabetic nephropathy.

Chronic Alcohol Consumption Results in Greater Damage to the Pancreas Than to the Liver in the Rats

Alcohol consumption increases the risk of type 2 diabetes. However, its effects on prediabetes or early diabetes have not been studied. We investigated endoplasmic reticulum (ER) stress in the pancreas and liver resulting from chronic alcohol consumption in the prediabetes and early stages of diabetes. We separated Otsuka Long-Evans Tokushima Fatty (OLETF) rats, a type-2 diabetic animal model, into two groups based on diabetic stage: prediabetes and early diabetes were defined as occurrence between the ages of 11 to 16 weeks and 17 to 22 weeks, respectively. The experimental group received an ethanol-containing liquid diet for 6 weeks. An intraperitoneal glucose tolerance test was conducted after 16 and 22 weeks for the prediabetic and early diabetes groups, respectively. There were no significant differences in body weight between the control and ethanol groups. Fasting and 120-min glucose levels were lower and higher, respectively, in the ethanol group than in the control group. In prediabetes rats, alcohol induced significant expression of ER stress markers in the pancreas; however, alcohol did not affect the liver. In early diabetes rats, alcohol significantly increased most ER stress-marker levels in both the pancreas and liver. These results indicate that chronic alcohol consumption increased the risk of diabetes in prediabetic and early diabetic OLETF rats; the pancreas was more susceptible to damage than was the liver in the early diabetic stages, and the adaptive and proapoptotic pathway of ER stress may play key roles in the development and progression of diabetes affected by chronic alcohol ingestion.

Short-Term Caloric Restriction Does Not Reduce Bone Mineral Density in Rats with Early Type 2 Diabetes

BACKGROUND: The effect of caloric restriction (CR) in the setting of diabetes on bone metabolism has not yet been fully studied. The aim of this study is to determine if short-term CR alters bone mass and metabolism in Otsuka Long-Evans Tokushima fatty (OLETF) rats, an animal model of type 2 diabetes. METHODS: Four groups (n=5) were created: OLETF rats with food ad libitum (AL), OLETF rats with CR, Long-Evans Tokusima Otsuka (LETO) rats with food AL, and LETO rats with CR. The CR condition was imposed on 24-week-old male rats using a 40% calorie reduction for 4 weeks. The effect of CR on femoral bone mineral density (BMD) was assessed by dual-energy X-ray absorptiometry. Serum markers were measured by immunoassay. RESULTS: After 4 weeks of CR, body weight decreased in both strains. The BMD decreased in LETO rats and was maintained in OLETF rats. After adjustment for body weight, BMD remained lower in LETO rats (P=0.017) but not OLETF rats (P=0.410). Bone-specific alkaline phosphatase levels decreased in LETO rats (P=0.025) but not in OLEFT rats (P=0.347). Serum leptin levels were reduced after CR in both strains, but hyperleptinemia remained in OLETF rats (P=0.009). CR increased 25-hydroxyvitamin D levels in OLETF rats (P=0.009) but not in LETO rats (P=0.117). Additionally, interleukin-6 and tumor necrosis factor-alpha levels decreased only in OLETF rats (P=0.009). CONCLUSION: Short-term CR and related weight loss were associated with decreases of femoral BMD in LETO rats while BMD was maintained in OLETF rats. Short-term CR may not alter bone mass and metabolism in type 2 diabetic rats.

Anti-diabetic effects of benfotiamine on an animal model of type 2 diabetes mellitus / 대한수의학회지

Although benfotiamine has various beneficial anti-diabetic effects, the detailed mechanisms underlying the impact of this compound on the insulin signaling pathway are still unclear. In the present study, we evaluated the effects of benfotiamine on the hepatic insulin signaling pathway in Otsuka Long-Evans Tokushima Fatty (OLETF) rats, which are a type 2 diabetes mellitus model. OLETF rats treated with benfotiamine showed decreased body weight gain and reduced adipose tissue weight. In addition, blood glucose levels were lower in OLETF rats treated with benfotiamine. Following treatment with benfotiamine, the levels of Akt phosphorylation (S473/T308) in the OLETF groups increased significantly compared to the OLETF control group so that they were almost identical to the levels observed in the control group. Moreover, benfotiamine restored the phosphorylation levels of both glycogen synthase kinase (GSK)-3alpha/beta (S21, S9) and glycogen synthase (GS; S641) in OLETF rats to nearly the same levels observed in the control group. Overall, these results suggest that benfotiamine can potentially attenuate type 2 diabetes mellitus in OLETF rats by restoring insulin sensitivity through upregulation of Akt phosphorylation and activation of two downstream signaling molecules, GSK-3alpha/beta and GS, thereby reducing blood glucose levels through glycogen synthesis.

Adipose Gene Expression Profiles Related to Metabolic Syndrome Using Microarray Analyses in Two Different Models

BACKGROUND: Peroxisome proliferator-activated receptor-gamma (PPAR-gamma) agonist has a wide-ranging influence on multiple components of metabolic syndrome. The Otsuka Long-Evans Tokushima Fatty (OLETF) rat is a useful animal model of metabolic syndrome. To determine genes related to metabolic syndrome, we examined overlapping genes that are simultaneously decreased by PPAR-gamma agonists and increased in OLETF rats using microarrays in two different models. METHODS: In the first microarray analysis, PPAR-gamma agonist-treated db/db mice were compared to standard diet-fed db/db mice. In the second microarray analysis, OLETF rats were compared to Long-Evans Tokushima Otsuka (LETO) rats (control of OLETF rats). RESULTS: Among the overlapping genes, in the present study, we validated that lipocalin-2 expression was significantly decreased in the visceral adipose tissue of PPAR-gamma agonist-treated db/db mice compared to standard diet-fed db/db mice and increased in OLETF rats compared to LETO rats using real time reverse transcription polymerase chain reaction. Furthermore, we showed for the first time that lipocalin-2 expression was significantly increased in the visceral adipose tissues of obese humans compared with nonobese humans. In addition, the expression level of lipocalin-2 in human visceral adipose tissue had a significant positive correlation with body mass index, serum interleukin-6, adipocyte fatty acid binding protein levels, and white blood cell count. CONCLUSION: Lipocalin-2 was confirmed to be a significant adipokine affected by PPAR-gamma agonist and obesity in the present study. Also, for the first time in human visceral adipose tissue, it was determined that the expression of lipocalin-2 from obese humans was significantly increased and correlated with circulating inflammatory markers.

Reduced Food Intake is the Major Contributor to the Protective Effect of Rimonabant on Islet in Established Obesity-Associated Type 2 Diabetes

PURPOSE: Although the presence of cannabinoid type 1 (CB1) receptor in islets has been reported, the major contributor to the protective effect of rimonabant on islet morphology is unknown. We determined whether the protective effect of rimonabant on pancreatic islet morphology is valid in established diabetes and also whether any effect was independent of decreased food intake. MATERIALS AND METHODS: After diabetes was confirmed, Otsuka Long-Evans Tokushima Fatty rats, aged 32 weeks, were treated with rimonabant (30 mg/kg/d, rimonabant group) for 6 weeks. Metabolic profiles and islet morphology of rats treated with rimonabant were compared with those of controls without treatment (control group), a pair-fed control group, and rats treated with rosiglitazone (4 mg/kg/d, rosiglitazone group). RESULTS: Compared to the control group, rats treated with rimonabant exhibited reduced glycated albumin levels (p<0.001), islet fibrosis (p<0.01), and improved glucose tolerance (p<0.05), with no differences from the pair-fed control group. The retroperitoneal adipose tissue mass was lower in the rimonabant group than those of the pair-fed control and rosiglitazone groups (p<0.05). Rimonabant, pair-fed control, and rosiglitazone groups showed decreased insulin resistance and increased adiponectin, with no differences between the rimonabant and pair-fed control groups. CONCLUSION: Rimonabant had a protective effect on islet morphology in vivo even in established diabetes. However, the protective effect was also reproduced by pair-feeding. Thus, the results of this study did not support the significance of islet CB1 receptors in islet protection with rimonabant in established obesity-associated type 2 diabetes.

Protective effects of Liuweidihuangwan on hepatic insulin resistance in OLETF rats / 南方医科大学学报

<p><b>OBJECTIVE</b>To investigate the mechanism through which Liuweidihuangwan improves hepatic insulin resistance in type 2 diabetic rats.</p><p><b>METHODS</b>With LETO rats as the normal control group, OLETF rats were treated daily with or without Liuweidihuangwan. At 8, 32, and 40 weeks of the treatment, 3 rats were randomly selected from each group for histological examination of the liver tissues and for detection of phosphoenolpyruvate carboxylase kinase (PEPCK) mRNA expression using RT-PCR and insulin receptor substrate-1 (IRS-1) and IRS-2 protein expressions using Western blotting.</p><p><b>RESULTS</b>Compared with LETO rats, OLETF rats showed progressive destruction of the lobular structures and hepatic steatosis in the liver over time. OLETF rats with Liuweidihuangwan treatment had basically normal lobular structure with only mild fatty degeneration in the liver. RT-PCR detection demonstrated a significantly higher PEPCK mRNA expression in untreated OLETF rats than in LETO rats (P<0.01), but a significantly lowered PEPCK expression in OLETF rats after Liuweidihuangwan dosing (P<0.01). Western blotting showed that significantly lower p-IRS-1 and p-IRS-2 protein expressions in untreated OLETF rats than those in LETO rats and treated OLTEF rats (P<0.05).</p><p><b>CONCLUSION</b>Liuweidihuangwan improves hepatic insulin resistance in OLETF rats by inhibiting the activity of gluconeogenic key enzyme (PEPCK) in the liver and enhancing IRS-1 and IRS-2 expressions in the insulin signaling pathway.</p>

Effect of liraglutide on interleukin-1β expression in the pancreatic islets of OLETF rats / 南方医科大学学报

<p><b>OBJECTIVE</b>To investigate the effect of liraglutide on the inflammatory cytokine interleukin-1β (IL-1β) and apoptotic factor caspase-3 expression in the pancreatic islets of OLETF rats with impaired glucose tolerance.</p><p><b>METHODS</b>Twelve-week-old OLETF rats were randomized into 4 groups and received intraperitoneal injections of saline or liraglutide at 50, 100, or 200 µg/kg twice daily for 12 weeks. Eight LETO rats served as the normal control group and received saline injection. After the treatments, the rats were examined for fasting and 30 min plasma insulin during OGTT test, and the expression levels of IL-1β and caspase-3 mRNA and protein in the pancreatic islets were detected by real-time PCR and Western blotting, respectively.</p><p><b>RESULTS</b>Compared with the saline group, liraglutide significantly decreased the expressions of IL-1β and caspase-3 mRNA and protein, and significantly improved the blood glucose, islet β function and early-phase insulin secretion index in OLETF rats.</p><p><b>CONCLUSIONS</b>Liraglutide can improve islet function and glucose metabolism partially by inhibiting islet IL-1β expression to delay or prevent the development of diabetes in OLETF rats.</p>

The Effect of Platelet-rich Plasma on Wounds of OLETF Rats Using Expression of Matrix Metalloproteinase-2 and -9 mRNA

BACKGROUND: Complicated diabetic patients show impaired, delayed wound healing caused by multiple factors. A study on wound healing showed that platelet-rich plasma (PRP) was effective in normal tissue regeneration. Nonetheless, there is no evidence that when plateletrich plasma is applied to diabetic wounds, it normalizes the diabetic wound healing process. In this study, we have analyzed matrix metalloproteinase (MMP)-2, MMP-9 expression to investigate the effect of PRP on diabetic wounds. METHODS: Twenty-four-week-old male Otsuka Long-Evans Tokushima Fatty rats were provided by the Tokushima Research Institute. At 50 weeks, wounds were arranged in two sites on the lateral paraspinal areas. Each wound was treated with PRP gel and physiologic saline gauze. To determine the expression of MMP-2, MMP-9, which was chosen as a marker of wound healing, reverse transcription polymerase chain reaction (RT-PCR) was performed and local distribution and expression of MMP-2, MMP-9 was also observed throughout the immunohistochemical staining. RESULTS: RT-PCR and the immunohistochemical study showed that the levels of MMP-2, MMP-9 mRNA expression in PRP applied tissues were higher than MMP-2, MMP-9 mRNA expression in saline-applied tissues. MMP-9 mRNA expression in wounds of diabetic rats decreased after healing began to occur. But no statistical differences were detected on the basis of body weight or fasting blood glucose levels. CONCLUSIONS: This study could indicate the extracellular matrix-regulating effect observed with PRP. Our results of the acceleration of wound healing events by PRP under hyperglycemic conditions might be a useful clue for future clinical treatment for diabetic wounds.

Kruppel-Like Factor 2 Suppression by High Glucose as a Possible Mechanism of Diabetic Vasculopathy

BACKGROUND AND OBJECTIVES: Endothelial dysfunction is widely observed in diabetes mellitus, resulting in diabetic vascular complications. Kruppel-like factor 2 (KLF2) is implicated as being a key molecule that maintains endothelial function. We evaluated the expression of KLF2 in endothelial cells cultured in high glucose and investigated its functional implication in a diabetic animal model. SUBJECTS AND METHODS: Human umbilical vein endothelial cells (HUVECs) were cultured in physiologically high glucose (35 mM) condition. The Otsuka Long Evans Tokushima Fatty (OLETF) strain of rat was used as an excellent model of obese type II diabetes, and their lean littermates are Long Evans Tokushima Otsuka (LETO) rats. RESULTS: In HUVECs cultured in physiologically high glucose condition, FOXO1 was activated whereas KLF2 and endothelial nitric oxide synthase (eNOS) expression was near completely abolished, which was completely reversed by FOXO1 small interfering ribonucleic acid. In the vessels harvested from the OLETF rats, the animal model of type II diabetes, KLF2 and eNOS expression were found depleted. When vascular remodeling was induced in the left common carotid artery by reduction of blood flow with partial ligation of the distal branches, greater neointimal hypertrophy was observed in OLETF rats compared with the control LETO rats. CONCLUSION: KLF2 suppression in endothelial cells by high glucose is a possible mechanism of diabetic endothelial dysfunction. The strategy of replenishing KLF2 may be effective for preventing diabetic vascular dysfunction.

Effect of Eplerenone, a Selective Aldosterone Blocker, on the Development of Diabetic Nephropathy in Type 2 Diabetic Rats

BACKGROUND: Aldosterone antagonists are reported to have beneficial effects on diabetic nephropathy by effective blocking of the renin-angiotensin-aldosterone system. We investigated the renoprotective effect of the selective aldosterone receptor blocker eplerenone, the angiotensin converting enzyme inhibitor lisinopril, and combined eplerenone and lisinopril treatment in type 2 diabetic rats. METHODS: Animals were divided into six groups as follows: Otsuka Long-Evans Tokushima Fatty (OLETF) rat control, OLETF rats treated with a low dose of eplerenone (50 mg/kg/day), OLETF rats treated with a high dose of eplerenone (200 mg/kg/day), OLETF rats treated with lisinopril (10 mg/kg/day), OLETF rats treated with a combination of both drugs (eplerenone 200 mg/kg/day and lisinopril 10 mg/kg/day), and obese non-diabetic Long-Evans Tokushima Otsuka rats for 26 weeks. RESULTS: Urinary albumin excretion was significantly lower in the lisinopril group, but not in the eplerenone group. Urinary albumin excretion was decreased in the combination group than in the lisinopril group. Glomerulosclerosis and renal expression of type I and type IV collagen, plasminogen activator inhibitor-1, transforming growth factor-beta1, connective tissue growth factor, and fibronectin mRNA were markedly decreased in the lisinopril, eplerenone, and combination groups. CONCLUSION: Eplerenone and lisinopril combination showed additional benefits on type 2 diabetic nephropathy compared to monotherapy of each drug.

Aqueous extract of Liriope platyphylla, a traditional Chinese medicine, significantly inhibits abdominal fat accumulation and improves glucose regulation in OLETF type II diabetes model rats / 한국실험동물학회지

Liriope platyphylla is a medical herb that has long been used in Korea and China to treat cough, sputum, neurodegenerative disorders, obesity, and diabetes. The aims of this study were to determine the antidiabetic and antiobesity effects of aqueous extract of L. platyphylla (AEtLP) through glucose and lipid regulation in both pre-diabetes and obesity stage of type II diabetes model. Two concentrations of AEtLP were orally administrated to OLETF (Otsuka Long-Evans Tokushima Fatty) rats once a day for 2 weeks, after which changes in glucose metabolism and fat accumulation were measured. Abdominal fat mass dramatically decreased in AEtLP-treated OLETF rats, whereas glucose concentration slightly decreased in all AEtLP-treated rats. However, compared to vehicle-treated OLETF rats, only AEtLP10 (10% concentration)-treated OLETF rats displayed significant induction of insulin production, whereas AEtLP5 (5% concentration)-treated OLETF rats showed a lower level of insulin. Although serum adiponectin level increased in only AEtLP5-treated rats, significant alteration of lipid concentration was detected in AEtLP5-treated OLETF rats. Expression of Glut-1 decreased in all AEtLP-treated rats, whereas Akt phosphorylation increased only in AEtLP10-treated OLETF rats. Furthermore, the pattern of Glut-3 expression was very similar with that of Glut-1 expression, which roughly corresponded with the phosphorylation of c-Jun N-teminal kinase (JNK) and p38 in the mitogen-activated protein kinase pathway. Therefore, these findings suggest that AEtLP should be considered as a therapeutic candidate during pre-diabetes and obesity stage capable of inducing insulin secretion from pancreatic beta-cells, glucose uptake in liver cells, as well as a decrease in fat and lipid accumulation.

Reduction of Food Intake by Fenofibrate is Associated with Cholecystokinin Release in Long-Evans Tokushima Rats

Fenofibrate is a selective peroxisome proliferator-activated receptor alpha (PPARalpha) activator and is prescribed to treat hyperlipidemia. The mechanism through which PPARalpha agonists reduce food intake, body weight, and adiposity remains unclear. One explanation for the reduction of food intake is that fenofibrate promotes fatty acid oxidation and increases the production of ketone bodies upon a standard experimental dose of the drug (100~300 mg/kg/day). We observed that low-dose treatment of fenofibrate (30 mg/kg/day), which does not cause significant changes in ketone body synthesis, reduced food intake in Long-Evans Tokushima (LETO) rats. LETO rats are the physiologically normal controls for Otsuka Long-Evans Tokushima Fatty (OLETF) rats, which are obese and cholecystokinin (CCK)-A receptor deficient. We hypothesized that the reduced food intake by fenofibrate-treated LETO rats may be associated with CCK production. To investigate the anorexic effects of fenofibrate in vivo and to determine whether CCK production may be involved, we examined the amount of food intake and CCK production. Fenofibrate-treated OLETF rats did not significantly change their food intake while LETO rats decreased their food intake. Treatment of fenofibrate increased CCK synthesis in the duodenal epithelial cells of both LETO and OLETF rats. The absence of a change in the food intake of OLETF rats, despite the increase in CCK production, may be explained by the absence of CCK-A receptors. Contrary to the OLETF rats, LETO rats, which have normal CCK receptors, presented a decrease in food intake and an increase in CCK production. These results suggest that reduced food intake by fenofibrate treatment may be associated with CCK production.