Otsuka Long-Evans Tokushima Fatty Group Research Articles

Exogenous T4 Increased Cardiac Thioredoxin Protein Expression in Insulin Resistant OLETF Rats

Thioredoxin (Trx) is a protein that regulates cellular signaling and antioxidant defense. Cellular antioxidant mechanisms are designed to protect cells from oxidative damage caused by inappropriately elevated reactive oxygen species (ROS) and other free radicals. Oxidative damage can lead to cellular damage and impaired function. Diabetic cardiomyopathy (CDM) is associated with impaired redox balance and oxidative injury. Altered fuel metabolism is a key feature of CDM characterized by an imbalance in fatty acid and glucose utilization, favoring fatty acid overutilization. Excessive fatty acid beta-oxidation in the mitochondria leads to generation of free radicals including superoxide, which can contribute to oxidative injury. Thyroid hormones regulate substrate utilization and their dysregulation may contribute to oxidative injury. Therefore, we hypothesized that exogenous thyroxine (exoT4) upregulates Trx protein expression and ameliorate oxidative injury in the hearts of insulin resistant rats. Insulin resistant, Otsuka Long Evans Tokushima Fatty (OLETF) rats were used to assess the effects of exoT4 on heart Trx, oxidative damage, and glucose metabolism. Rats were assigned to four groups: (1) lean, control Long Evans Tokushima Otsuka (LETO; n=6), (2) LETO + T4 (8 μg/100g BM/d × 5 wks; n=7), (3) untreated, insulin resistant OLETF (n=6), and (4) OLETF + T4 (n=7). OLETF group displayed a 31% decreased in TRX compared to Leto. T4 increased Trx protein expression by 88% in OLTEF compared to untreated OLETF. This data suggests that exoT4 has the potential to upregulate cardiac Trx-dependent antioxidant mechanisms in insulin resistant OLETF rats to ameliorate oxidative injury and improve cardiac glucose metabolism. This work is supported by the American Heart Association and the Undergraduate Research Opportunity Center (UROC). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Exogenous Thyroxine Increases Cardiac AS160 Phosphorylation in Insulin Resistant OLETF Rats

Thyroxine (T4) is the most abundant thyroid hormone secreted by thyroid gland and contributes to glucose metabolism via both insulin and non-insulin dependent pathways. Akt substrate 160 (AS160) is a Rab-GDP activating protein and a downstream effector of protein kinase B (Akt) required for glucose transport and upregulation of GLUT4 activating vesicle (GSV). The phosphorylation of AS160 (p-AS160) is required for the regulation of GLUT4 translocation to the membrane. It is also involved in insulin-mediated traffcking of GLUT4 in skeletal muscle and adipose tissues. The accumulation of AS160 has also been implicated in promoting cardiac hypertrophy, which is commonly associated with the metabolic syndrome (MetS). This study explores how thyroid hormones can affect the phosphorylation status of cardiac AS160 during insulin resistance. Under normal conditions, AS160 is phosphorylated by Akt to upregulate GSV, allowing glucose to cross the cell membrane through GLUT4. We hypothesize that exogenous T4 increases cardiac phosphorylation of AS160 expression during insulin resistance. Insulin resistant, Otsuka Long Evans Tokushima Fatty (OLETF) rats were used to assess the effects of exogenous thyroxine (T4) on cardiac p-AS160. Rats were assigned to four groups: (1) lean, Long Evans Tokushima Otsuka (LETO; n=6), (2) LETO + T4 (8 μg/100g BM/d × 5 wks; n=7), (3) untreated OLETF (n=6), and (4) OLETF + T4 (n=7). Exogenous T4 did not significantly alter native AS160 protein expression among all four groups. However, p-AS160 was reduced in the non-treated OLETF group by 61% (p<0.01) compared to healthy LETO control group. Exogenous T4 increased p-AS160 by 16% (p<0.05) compared to non-treated OLETF group and by 36% (p<0.05) in treated LETO compared to control LETO group. We have previously demonstrated that exogenous T4 increased the translocation of cardiac GLUT4 and the present findings suggest that this increased translocation is mediated by activation of AS160, resulting in improved glucose metabolism in the heart during insulin resistance. American Heart Association. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

The Effect of Resistance Exercise on Myocardial Inflammatory Cytokines and ERK1/2 Expression in Type 2 Diabetic Rats

PURPOSE: The purpose of this study was to investigate the effect of resistance ladder exercise on myocardial inflammatory cytokines and extracellular signal regulated kinase (ERK)1/2 expression in type 2 diabetic rats.METHODS: A total of 21 8-week-old male Long Evans Tokushima Otsuka (LETO) and Otsuka Long Evans Tokushima Fatty (OLETF) rats were divided into three groups: LETO group (CON, n=7), OLETF group (DM, n=7), and resistance exercise group (DM+EXE, n=7). Resistance exercise referred to a climbing exercise on a slope. The rats performed this exercise 3 full d per week, for 8 week. The expression of myocardial inflammatory cytokines and ERK1/2 was analyzed via western blotting after 8 week of exercise intervention.RESULTS: After 8 weeks of resistance exercise for the management of type 2 diabetes, the production of anti-inflammatory factor Interleukin (IL)-10 in the myocardium increased. This inhibited the production of pro-inflammatory factors IL-6 and tumor necrosis factor-alpha. However, resistance exercise did not affect the expression of ERK1 and ERK2, which are apoptosis regulatory proteins.CONCLUSIONS: In type 2 diabetes, resistance exercise is thought to be effective in reducing inflammatory factors by mediating cytokines. Although the effects of resistance ladder exercise were confirmed, further studies on a variety of exercise types and intensities should be conducted to prevent and improve the conditions of those with diabetes.

Allopurinol ameliorates high fructose diet induced hepatic steatosis in diabetic rats through modulation of lipid metabolism, inflammation, and ER stress pathway

Excess fructose consumption contributes to development obesity, metabolic syndrome, and nonalcoholic fatty liver disease (NAFLD). Uric acid (UA), a metabolite of fructose metabolism, may have a direct role in development of NAFLD, with unclear mechanism. This study aimed to evaluate role of fructose and UA in NAFLD and explore mechanisms of allopurinol (Allo, a UA lowering medication) on NAFLD in Otsuka Long-Evans Tokushima Fatty (OLETF) rats fed a high fructose diet (HFrD), with Long-Evans Tokushima Otsuka (LETO) rats used as a control. There were six groups: LETO, LETO-Allo, OLETF, OLETF-Allo, OLETF-HFrD, and OLETF-HFrD-Allo. HFrD significantly increased body weight, epididymal fat weight, and serum concentrations of UA, cholesterol, triglyceride, HbA1c, hepatic enzymes, HOMA-IR, fasting insulin, and two hour-glucose after intraperitoneal glucose tolerance tests, as well as NAFLD activity score of liver, compared to the OLETF group. Allopurinol treatment significantly reduced hepatic steatosis, epididymal fat, serum UA, HOMA-IR, hepatic enzyme levels, and cholesterol in the OLETF-HFrD-Allo group. Additionally, allopurinol significantly downregulated expression of lipogenic genes, upregulated lipid oxidation genes, downregulated hepatic pro-inflammatory cytokine genes, and decreased ER-stress induced protein expression, in comparison with the OLETF-HFrD group. In conclusion, allopurinol ameliorates HFrD-induced hepatic steatosis through modulation of hepatic lipid metabolism, inflammation, and ER stress pathway. UA may have a direct role in development of fructose-induced hepatic steatosis, and allopurinol could be a candidate for prevention or treatment of NAFLD.

Caloric Restriction Increases Parkin Recruitment in Hearts of Obese Insulin‐Resistant Rats

Mitochondria provide energy to the cells, making the task of mitochondrial recycling highly important. Impairments in mitochondrial number and function can lead to dysregulation of cellular metabolism and disrupted capacity to maintain homeostasis. The Parkin gene codes for the protein, Parkin, which is a component of the Parkin/PINK1 pathway that helps regulate mitophagy. An impairment in the Parkin gene may also results in nonfunctional mitochondria, potentially leading to many diseases such as type two diabetes mellitus and cardiovascular disease. Recent studies suggest that Parkin expression is downregulated during insulin resistance. To address the hypothesis that insulin resistance downregulates Parkin in the heart, a piece of the left ventricle of the hearts of 4 groups of rats were extracted: (1) Long Evans Tokushima Otsuka (LETO), (2) Otsuka Long‐Evans Tokushima Fatty (OLETF), (3) LETO with caloric restriction, and (4) OLETF with caloric restriction. Extracted Parkin from the hearts of each group was measured by Western blot. Because Parkin expression is downregulated with insulin resistance, we anticipated lower levels of express in the insulin resistant, OLETF rats compared to LETO, and that caloric restriction would restore Parkin expression in the OLETF rats. Parkin protein expression was 71% lower in OLETF than LETO. While the 16% increase in expression in caloric restricted LETO group was not statistically significant, the expression increased nearly 7.5‐fold with caloric restriction in OLETF group compared to the ad lib OLETF group. The data suggest that the benefits of CR on CV function and health go beyond the potential benefits of mass loss (usually adiposity) but include cellular energetics and metabolism in the heart of insulin resistant rats.Support or Funding InformationThe STRIDE Fellowship is supported by the American Physiological Society and a grant from the National Heart, Lung and Blood Institute (NHLBI; 1 R25 HL115473‐01).This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Effect of sodium-glucose cotransporter 2 inhibitor, empagliflozin, and α-glucosidase inhibitor, voglibose, on hepatic steatosis in an animal model of type 2 diabetes.

We investigated the effects of sodium-glucose cotransporter 2 inhibitor, empagliflozin, and α-glucosidase inhibitor, voglibose, on hepatic steatosis in an animal model of type 2 diabetes (T2DM). Empagliflozin (OLETF-EMPA) or voglibose (OLETF-VOG) was administered to Otsuka Long-Evans Tokushima fatty (OLETF) rats once daily for 12 weeks. Control Long-Evans Tokushima Otsuka (LETO) and OLETF (OLETF-C) rats received saline. Blood glucose levels were significantly suppressed in OLETF-EMPA and OLETF-VOG compared with the OLETF-C group. The liver fat content was significantly higher in the OLETF-C group than in the OLETF-EMPA and OLETF-VOG. Hepatic gene expressions involved in gluconeogenesis (glucose 6-phosphatase [G6Pase], fructose-1,6-bisphosphatase [FBP1], and phosphoenolpyruvate carboxykinase [PEPCK]) and lipogenesis (acetyl-CoA carboxylase [ACC], fatty acid synthase [FAS], and sterol regulatory element-binding transcription factor 1c [SREBP-1c]) were significantly decreased in the OLETF-EMPA group compared with other OLETF groups (OLETF-C and OLETF-VOG). Sirtuin 1 (SIRT1) expression level and SIRT1 activity were markedly reduced in OLETF-C rats; however, its expression increased in the OLETF-EMPA and OLETF-VOG. AMP-activated protein kinase (AMPK) phosphorylation level was remarkably increased by empagliflozin treatment in OLETF rats compared with other OLETF groups. Long-term empagliflozin and voglibose treatment reduced hepatic steatosis with suppression of gluconeogenesis and lipogenesis pathway in OLETF rats. We suggest that this metabolic improvement might be related to SIRT1 and AMPK pathway in T2DM. But empagliflozin is thought to have more advantage to prevent hepatic steatosis than voglibose in T2DM.

Simultaneous GLP-1 receptor activation and angiotensin receptor blockade increase natriuresis independent of altered arterial pressure in obese OLETF rats

Obesity is associated with an inappropriately activated renin-angiotensin-aldosterone system, suppressed glucagon-like peptide-1 (GLP-1), increased renal Na+ reabsorption, and hypertension. To assess the link between GLP-1 and angiotensin receptor type 1 (AT1) signaling on obesity-associated impairment of urinary Na+ excretion (UNaV) and elevated arterial pressure, we measured mean arterial pressure (MAP) and heart rate by radiotelemetry and metabolic parameters for 40 days. We tested the hypothesis that stimulation of GLP-1 signaling provides added benefit to blockade of AT1 by increasing UNaV and further reducing arterial pressure in the following groups: (1) untreated Long-Evans Tokushima Otsuka (LETO) rats (n = 7); (2) untreated Otsuka Long-Evans Tokushima Fatty (OLETF) rats (n = 9); (3) OLETF + ARB (ARB; 10 mg olmesartan/kg/day; n = 9); (4) OLETF + GLP-1 receptor agonist (EXE; 10 µg exenatide/kg/day; n = 7); and (5) OLETF + ARB + EXE (Combo; n = 6). On day 2, UNaV was 60% and 62% reduced in the EXE and Combo groups, respectively, compared with that in the OLETF rats. On day 40, UNaV was increased 69% in the Combo group compared with that in the OLETF group. On day 40, urinary angiotensinogen was 4.5-fold greater in the OLETF than in the LETO group and was 56%, 62%, and 58% lower in the ARB, EXE, and Combo groups, respectively, than in the OLETF group. From day 2 to the end of the study, MAP was lower in the ARB and Combo groups than in the OLETF rats. These results suggest that GLP-1 receptor activation may reduce intrarenal angiotensin II activity, and that simultaneous blockade of AT1 increases UNaV in obesity; however, these beneficial effects do not translate to a further reduction in MAP.

Alteration of Vascular Responsiveness to Uridine Adenosine Tetraphosphate in Aortas Isolated from Male Diabetic Otsuka Long-Evans Tokushima Fatty Rats: The Involvement of Prostanoids.

We investigated whether responsiveness to dinucleotide uridine adenosine tetraphosphate (Up4A) was altered in aortas from type 2 diabetic Otsuka Long-Evans Tokushima Fatty (OLETF) rats compared with those from age-matched control Long-Evans Tokushima Otsuka (LETO) rats at the chronic stage of disease. In OLETF aortas, we observed the following: (1) Up4A-induced contractions were lower than those in the LETO aortas under basal conditions, (2) slight relaxation occurred due to Up4A, but this was not observed in phenylephrine-precontracted LETO aortas, (3) acetylcholine-induced relaxation was reduced (vs. LETO), and (4) prostanoid release (prostaglandin (PG)F2α, thromboxane (Tx)A2 metabolite, and PGE2) due to Up4A was decreased (vs. LETO). Endothelial denudation suppressed Up4A-induced contractions in the LETO group, but increased the contractions in the OLETF group. Under nitric oxide synthase (NOS) inhibition, Up4A induced contractions in phenylephrine-precontracted aortas; this effect was greater in the LETO group (vs. the OLETF group). The relaxation response induced by Up4A was unmasked by cyclooxygenase inhibitors, especially in the LETO group, but this effect was abolished by NOS inhibition. These results suggest that the relaxant component of the Up4A-mediated response was masked by prostanoids in the LETO aortas and that the LETO and OLETF rats presented different contributions of the endothelium to the response.

Quantitative susceptibility mapping in a diabetes mellitus rat model: Iron accumulation in the brain

AbstractThis study evaluated the susceptibility effects using quantitative susceptibility mapping (QSM) as a marker for regional brain iron alternations in diabetic rat brains. Otsuka Long‐Evans Tokushima Fatty (OLETF) rats (n = 7) and age‐matched lean Long‐Evans Tokushima Otsuka (LETO) control rats (n = 8) were scanned using a three‐dimensional gradient‐echo sequence in a 3 Tesla MRI to map QSM. The correlation analysis was performed to evaluate the relationship between the QSM value and the body weight and the fasting blood glucose value of the rats. QSM values in the OLETF group were significantly increased in hippocampi and thalami, as compared with those of the LETO group. The QSM values of the OLETF rats were negatively correlated with the body weight in putamen and were significantly correlated with the fasting blood glucose level in the left amygdala and right thalamus. With higher QSM values in diabetic rats than in control rats, QSM values in the diabetic group were significantly correlated with the body weight and the fasting blood glucose level, indicating that the QSM technique should be helpful to noninvasively investigate iron overload in the diabetic brain.

Augmented Contractility to Noradrenaline in Femoral Arteries from the Otsuka Long-Evans Tokushima Fatty Rat, a Model of Type 2 Diabetes

Although vasculopathies may occur systemically, there are few reports regarding femoral arteries of type 2 diabetes. Here, we investigated whether contractile response to noradrenaline in femoral arteries would change in type 2 diabetic male Otsuka Long-Evans Tokushima Fatty (OLETF) rat at the chronic stage of disease (1 year old) versus age-matched control Long-Evans Tokushima Otsuka (LETO) rat. OLETF rat exhibited hyperglycemia, hypertension, hyperlipidemia, and hypoinsulinemia compared to age-matched LETO rat. Noradrenaline-induced contraction was increased in femoral arteries in OLETF rats compared with LETO rats whereas serotonin- or phenylephrine-induced contractions were similar between these two animals. Acetylcholine- and sodium nitroprusside-induced relaxations were similar between the two groups. Very small relaxations in femoral arteries induced by clonidine and isoprenaline were obtained in LETO but not OLETF group. Noradrenaline-induced contraction was enhanced by treatment with NG-nitro-L-arginine (L-NNA), a nitric oxide synthase (NOS) inhibitor, and the between-group difference of contraction was eliminated by such treatment. Indomethacin, a non-selective cyclooxygenase (COX) inhibitor, reduced noradrenaline-induced contraction in both groups, whereas the contraction was greater in OLETF group versus LETO. Femoral arterial protein expression of endothelial NOS, COX-1, and superoxide dismutases were similar between the two groups, whereas reduction of COX-2 expression was seen in OLETF group compared with LETO. Increased contractile responsiveness to noradrenaline is seen in OLETF rat femoral artery and this may be due to reduction of suppressive effect of NO.

Chronic saponin treatment attenuates damage to the pancreas in chronic alcohol-treated diabetic rats

BackgroundChronic heavy alcohol consumption may raise the risk of developing type 2 diabetes mellitus. Saponins inhibit apoptosis of pancreatic islet cells and reduce lipid parameters. The present study was designed to investigate the effect of saponin on chronic ethanol-treated diabetic rats. MethodsLong–Evans Tokushima Fatty (LETO) and Otsuka Long–Evans Tokushima Fatty (OLETF) rats were pair-fed a Lieber–DeCarli diet with and without 5% ethanol for 12 wks. Two weeks after starting the pair-feeding with the Lieber–DeCarli diet, intraperitoneal injection of saponin was performed for 10 wks. To perform the experiments, rats were divided as follows: LETO-Control (LC), LETO-Ethanol (LE), LETO-Ethanol-Saponin (LES), OLETF-Control (OC), OLETF-Ethanol (OE), and OLETF-Ethanol-Saponin (OES). ResultsThe weights of epididymal and mesenteric fat tissue in LES and OES rats were the lightest from among the LETO and OLETF groups, respectively. The secretion of alanine aminotransferase and cholesterol in OES rats decreased significantly compared to their secretion in OC and OE rats, respectively. The islets of the pancreas in LE and OE rats showed clean, unclear, and smaller morphology compared to those of LC, LES, OC, and OES rats. In addition, the expression of insulin in the islets of the pancreas in LC, LES, OC, and OES rats was higher than in LE and OE rats. ConclusionSaponin may not only be helpful in alleviating the rapid progress of diabetes due to chronic alcohol consumption in diabetic patients, but may also show potential as an antidiabetic drug candidate for diabetic patients who chronically consume alcohol.

A return to ad libitum feeding following caloric restriction promotes hepatic steatosis in hyperphagic OLETF rats.

Hyperphagic Otsuka Long-Evans Tokushima fatty (OLETF) rats develop obesity, insulin resistance, and nonalcoholic fatty liver disease (NAFLD), but lifestyle modifications, such as caloric restriction (CR), can prevent these conditions. We sought to determine if prior CR had protective effects on metabolic health and NAFLD development following a 4-wk return to ad libitum (AL) feeding. Four-week-old male OLETF rats (n = 8-10/group) were fed AL for 16 wk (O-AL), CR for 16 wk (O-CR; ∼70% kcal of O-AL), or CR for 12 wk followed by 4 wk of AL feeding (O-AL4wk). CR-induced benefit in prevention of NAFLD, including reduced hepatic steatosis, inflammation, and markers of Kupffer cell activation/number, was largely lost in AL4wk rats. These findings occurred in conjunction with a partial loss of CR-induced beneficial effects on obesity and serum triglycerides in O-AL4wk rats, but in the absence of changes in serum glucose or insulin. CR-induced increases in hepatic mitochondrial respiration remained significantly elevated (P < 0.01) in O-AL4wk compared with O-AL rats, while mitochondrial [1-(14)C]palmitate oxidation, citrate synthase activity, and β-hydroxyacyl-CoA dehydrogenase activity did not differ among OLETF groups. NAFLD development in O-AL4wk rats was accompanied by increases in the protein content of the de novo lipogenesis markers fatty acid synthase and stearoyl-CoA desaturase-1 and decreases in phosphorylated acetyl-CoA carboxylase (pACC)/ACC compared with O-CR rats (P < 0.05 for each). The beneficial effects of chronic CR on NAFLD development were largely lost with 4 wk of AL feeding in the hyperphagic OLETF rat, highlighting the importance of maintaining energy balance in the prevention of NAFLD.

Assessment of Androgen Replacement Therapy for Erectile Function in Rats with Type 2 Diabetes Mellitus by Examining Nitric Oxide-Related and Inflammatory Factors

Type 2 diabetes mellitus (T2DM) has become a major public health issue and is considered a risk factor for erectile dysfunction (ED). T2DM is also associated with androgen deficiency. However, there have been few basic studies on androgen replacement therapy (ART) for ED treatment in T2DM animal models, and the mechanism underlying the effect of ART on T2DM-induced ED is unclear. To investigate the effect of ART on ED in T2DM rats by examining inflammatory and nitric oxide (NO)-related factors. Otsuka Long-Evans Tokushima Fatty (OLETF) rats and their controls, Long-Evans Tokushima Otsuka (LETO) rats, were distributed into three groups: LETO, OLETF, and ART. In the ART group, OLETF rats were treated daily with testosterone (3 mg/kg/day, subcutaneously) from 20 to 25 weeks of age; LETO and OLETF rats received vehicle only. We measured erectile function by using measurements of the ratio between intracavernosal pressure (ICP) and mean arterial pressure (MAP) following electrical stimulation of the cavernous nerve and by evaluating the endothelial function of the corpus cavernosum in an isometric tension study. Expression of endothelial NO synthase (eNOS), inducible NO synthase (iNOS), sirtuin-1 (Sirt1), interleukin-6 (IL-6), and tumor necrosis factor alpha (TNF-α) mRNA was detected using polymerase chain reaction. The ICP/MAP ratio in the OLETF group was significantly decreased and that in the ART group was significantly improved (P < 0.01). The response to acetylcholine was significantly decreased in the OLETF group and improved in the ART group (P < 0.01). Although expression of eNOS and Sirt1 mRNA was decreased and that of iNOS, IL-6, and TNF-α mRNA was increased in the OLETF group, ART improved mRNA expression. ART suppressed inflammation in rats with T2DM and metabolic disorders and improved their endothelial and erectile functions. ART could be effective for T2DM-induced ED and may be considered a potential ED treatment method.

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Urinary Sodium Excretion Decreases In the Early Stages of Insulin Resistance In Model of Metabolic Syndrome Melissa E. Williams1, Jacqueline N. Minas1, Ruben Rodriguez1, Daisuke Nakano2, Akira Nishiyama2, and Rudy M. Ortiz11Department of Molecular &amp; Cellular Biology, School of Natural Science, University of California Merced 2Department of Pharmacology, Kagawa Medical University, Kagawa, Japan Type II diabetes is associated with abnormal activation of the renin‐angiotensin aldosterone system and impaired sodium (Na+) regulation contributing to volume dependent hypertension. However, the mechanisms contributing to elevated systolic blood pressure (SBP) during the development of insulin resistance (IR) are not well defined. To examine the effects of the onset of IR to impaired UNaV and SBP, three groups of rats were studied for 6 weeks (n=6/group); 1) non‐IR, Long Evans Tokushima Otsuka (LETO), 2) untreated, IR Otsuka Long Evans Tokushima Fatty (OLETF), 3) OLETF + angiotensin receptor blocker (ARB; 10 mg olmesartan/kg/d for 3 weeks). Systolic blood pressure (SBP), urine Na+ excretion (UNaV), and insulin resistance index (IRI) were measured at 9 and 15 weeks of age. At 9 weeks of age, the OLETF group exhibited a 43% increase in IRI compared to the LETO group. However, no differences in SBP and UNaV between LETO and OLETF were observed. At 15 weeks of age, the OLETFs experienced a 54% increase in IRI, accompanied by a 15% (145 mmHg) increase in mean SBP at 15 weeks, which was attributed to the 46% decrease in mean UNaV. This suggests that IR causes impaired renal Na+ regulation, contributing to the onset of hypertension. Conversely, ARB treatment in OLETFs reduced SBP by 25% and increased UNaV by 50%, as well as a 24% decrease in IRI. This indicates that inappropriate activation of AT1 contributes to IR‐associated hypertension observed in OLETF.

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

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)- (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- and GS, thereby reducing blood glucose levels through glycogen synthesis.

Diesel Exhaust Particle-Induced Airway Responses are Augmented in Obese Rats

Air pollutants and obesity are important factors that contribute to asthma. The aim of this study was to assess the airway responsiveness and inflammation in Otsuka-Long Evans Tokushima Fatty (OLETF) obese rats and Long Evans Tokushima-Otsuka (LETO) nonobese rats exposed to diesel exhaust particles (DEPs). Otsuka Long Evans Tokushima fatty rats and LETO rats were exposed intranasally to DEP and then challenged with aerosolized DEP on days 6 to 8. Body plethysmography, bronchoalveolar lavage (BAL), and histology were performed. Enhanced pause (Penh) was measured as an indicator of airway resistance on day 9 and samples were collected on day 10. After exposure to DEP, the OLETF group exhibited a greater increase in Penh compared to that in the LETO group. Moreover, the BAL fluid in mice showed an increase in the total and differential cell counts in the DEP-exposed OLETF group compared to that in the DEP-exposed LETO group. Histological assessment of lung tissue from each group revealed that the DEP-exposed OLETF group tended to have increased inflammatory cell infiltrations in the prebronchial area. Increased peroxisome proliferator-activated receptor γ, coactivator 1β messenger RNA was observed in the lungs of obese rats compared to that in nonobese rats following DEP exposure. These data indicate that the DEP-exposed OLETF group had increased airway responses and inflammation compared to the DEP-exposed LETO group, indicating that diesel particulates and obesity may be co-contributors to asthma.

Impaired Survival of Autologous Fat Grafts by Diabetes Mellitus in an Animal Model: A Pilot Study

Many surgeons are reluctant to perform fat grafting in patients with diabetes because soft-tissue healing is impaired, but no previous study has reported data-driven outcomes of fat grafting in subjects with diabetes. The authors investigate whether diabetes affected survival and complication rates of autologous fat grafting (AFG) in Sprague-Dawley (SD) and Otsuka Long-Evans Tokushima Fatty (OLETF) rats. In total, 16 male SD and 16 male OLETF rats were prepared for AFG. Fat tissue was harvested from the inguinal fat pad and cut into 1-g (800-1250 mg) sections. Each rat received fat in a subcutaneous pocket in the paraspinal area. The grafted fat tissue was measured by ultrasonography at 30, 60, and 90 days after implantation and evaluated by histological analyses. Ultrasonographic analysis indicated that compared with the SD group, the AFG survival rate was lower in OLETF rats (40.52% vs 53.38%), and the failure rate was higher in OLETF rats (31.25% vs 6.25%). The histological analysis indicated that compared with the OLETF group, adipocytes were more dense (3.18 vs 2.33; P = .025), cyst formation occurred less frequently (3.00 vs 3.61; P = .030), and more capillaries were formed (2.31/field vs 1.61/field; P = .001) in the SD rat group. Diabetes causes marked deterioration in the survival and quality of AFG in the diabetic rat model.

Combination of a peroxisome proliferator-activated receptor-gamma agonist and an angiotensinII receptor blocker attenuates myocardial fibrosis and dysfunction in type2 diabetic rats.

We aimed to examine the effect of an angiotensinII receptor blocker (ARB), a peroxisome proliferator-activated receptor (PPAR)-gamma agonist, and their combination on myocardial fibrosis and function in type2 diabetic rats. Five male Long-Evans Tokushima Otsuka (LETO) rats and 20 male Otsuka Long-Evans Tokushima Fatty (OLETF) rats were used. OLETF rats were assigned to four groups (n=5 per group) at 28weeks-of-age: untreated, losartan-treated, rosiglitazone-treated and combination-treated. The ARB, losartan, was administered at a dose of 5mg/kg/day, and the PPAR-gamma agonist, rosiglitazone, was administered at a dose of 3mg/kg/day by oral gavage for 12weeks. Urine and blood samples were collected, and two-dimensional echocardiograms and strain rate imaging were obtained at 28 and 40weeks. Cytokines were evaluated by reverse transcriptase polymerase chain reaction, and histological analysis was carried out at 40weeks. At 40weeks, the global radial strains of the losartan-treated (55.7±4.5%, P=0.021) and combination-treated groups (59.3±6.7%, P=0.001) were significantly higher compared with the untreated OLETFs (44.3±10.5%). No difference was observed when compared with LETO rats. Although the rosiglitazone-treated group showed a better metabolic profile than the untreated OLETF group, there was no difference in the global radial strain (49.8±6.0 vs 44.3±10.5, P=0.402). The expression of pro-inflammatory cytokines, and collagen typeI and III were consistently attenuated in the losartan-treated and combination-treated OLETF groups, but not in the rosiglitazone-treated group. A combination of rosiglitazone and losartan attenuates myocardial fibrosis and dysfunction in type2 diabetic rats.

Effects of endurance exercise training, metformin, and their combination on adipose tissue leptin and IL-10 secretion in OLETF rats

Adipose tissue inflammation plays a role in cardiovascular (CV) and metabolic diseases associated with obesity, insulin resistance, and type 2 diabetes mellitus (T2DM). The interactive effects of exercise training and metformin, two first-line T2DM treatments, on adipose tissue inflammation are not known. Using the hyperphagic, obese, insulin-resistant Otsuka Long-Evans Tokushima Fatty (OLETF) rat model, we tested the hypothesis that treadmill training, metformin, or a combination of these reduces the secretion of proinflammatory cytokines from adipose tissue. Compared with Long-Evans Tokushima Otsuka (LETO) control rats (L-Sed), sedentary OLETF (O-Sed) animals secreted significantly greater amounts of leptin from retroperitoneal adipose tissue. Conversely, secretion of interleukin (IL)-10 by O-Sed adipose tissue was lower than that in L-Sed animals. Examination of leptin and IL-10 secretion from adipose tissue in OLETF groups treated with endurance exercise training (O-EndEx), metformin treatment (O-Met), and a combination of these (O-E+M) from 20 to 32 wk of age indicated that 1) leptin secretion from adipose tissue was reduced in O-Met and O-E+M, but not O-EndEx animals; 2) adipose tissue IL-10 secretion was increased in O-EndEx and O-E+M but not in O-Met animals; and 3) only the combined treatment (O-E+M) displayed both a reduction in leptin secretion and an increase in IL-10 secretion. Leptin and IL-10 concentrations in adipose tissue-conditioned buffers were correlated with their plasma concentrations, adipocyte diameters, and total adiposity. Overall, this study indicates that exercise training and metformin have additive influences on adipose tissue secretion and plasma concentrations of leptin and IL-10.

Effects of Endurance Exercise Training, Metformin, and Their Combination on Adipose Tissue Cytokine Secretion in a Rat Model of Type 2 Diabetes (T2D)

Otsuka Long Evans Tokushima Fatty (OLETF) rats are a hyperphagic and obese rodent model of T2D. We randomly assigned OLETF rats (age 20 wks, the onset of insulin resistance) to sedentary (SED), endurance exercise training (TR; 20 m/min, 60 min/d, 5 d/wk running), metformin (MET; 300 mg/kg/d in drinking water), or TR + MET groups. Age‐matched SED Long‐Evans Tokushima Otsuka (LETO) rats served as controls. At sacrifice (age 30–32 wks), retroperitoneal (RP) fat pads were harvested and incubated in Krebs solution for 60 min at 37°C. RP fat‐conditioned buffers were assayed for interleukin‐6 (IL‐6), leptin, monocyte chemoattractant protein‐1 (MCP‐1), and tumor necrosis factor‐α (TNF‐α). Compared to LETO RP fat, sedentary OLETF RP fat secreted ~30%, ~200%, ~15%, and ~50% more IL‐6, leptin, MCP‐1, and TNF‐α, respectively. Preliminary analysis of treatment effects revealed that: (i) MET alone or TR + MET, but not TR alone, normalized differences between OLETF and LETO groups in IL‐6 and TNF‐α secretion; (ii) only MET, but neither TR nor TR + MET, normalized MCP‐1 secretion; (iii) TR and TR + MET, but not MET alone, normalized leptin secretion. Leptin levels in RP fat‐conditioned buffer correlated with plasma leptin across all groups (r2 = 0.78, P &lt; 0.01). These data suggest that MET decreases adipose tissue inflammatory cytokine release and that TR decreases adipose tissue leptin secretion in T2D.