Lean Zucker Rats Research Articles

Upregulation of orexin receptor in paraventricular nucleus promotes sympathetic outflow in obese Zucker rats

Sympathetic vasomotor tone is elevated in obesity-related hypertension. Orexin importantly regulates energy metabolism and autonomic function. We hypothesized that alteration of orexin receptor in the paraventricular nucleus (PVN) of the hypothalamus leads to elevated sympathetic vasomotor tone in obesity. We used in vivo measurement of sympathetic vasomotor tone and microinjection into brain nucleus, whole-cell patch clamp recording in brain slices, and immunocytochemical staining in obese Zucker rats (OZRs) and lean Zucker rats (LZRs). Microinjection of orexin 1 receptor (OX1R) antagonist SB334867 into the PVN reduced basal arterial blood pressure (ABP) and renal sympathetic nerve activity (RSNA) in anesthetized OZRs but not in LZRs. Microinjection of orexin A into the PVN produced greater increases in ABP and RSNA in OZRs than in LZRs. Western blot analysis revealed that OX1R expression levels in the PVN were significantly increased in OZRs compared with LZRs. OX1R immunoreactivity was positive in retrogradely labeled PVN-spinal neurons. The basal firing rate of labeled PVN-spinal neurons was higher in OZRs than in LZRs. SB334867 decreased the basal firing activity of PVN-spinal neurons in OZRs but had no effect in LZRs. Orexin A induced a greater increase in the firing rate of PVN-spinal neurons in OZRs than in LZRs. In addition, orexin A induced larger currents in PVN-spinal neurons in OZRs than in LZRs. These data suggest that upregulation of OX1R in the PVN promotes hyperactivity of PVN presympathetic neurons and elevated sympathetic outflow in obesity.

Alagebrium inhibits neointimal hyperplasia and restores distributions of wall shear stress by reducing downstream vascular resistance in obese and diabetic rats.

Mechanisms of restenosis in type 2 diabetes mellitus (T2DM) are incompletely elucidated, but advanced glycation end-product (AGE)-induced vascular remodeling likely contributes. We tested the hypothesis that AGE-related collagen cross-linking (ARCC) leads to increased downstream vascular resistance and altered in-stent hemodynamics, thereby promoting neointimal hyperplasia (NH) in T2DM. We proposed that decreasing ARCC with ALT-711 (Alagebrium) would mitigate this response. Abdominal aortic stents were implanted in Zucker lean (ZL), obese (ZO), and diabetic (ZD) rats. Blood flow, vessel diameter, and wall shear stress (WSS) were calculated after 21 days, and NH was quantified. Arterial segments (aorta, carotid, iliac, femoral, and arterioles) were harvested to detect ARCC and protein expression, including transforming growth factor-β (TGF-β) and receptor for AGEs (RAGE). Downstream resistance was elevated (60%), whereas flow and WSS were significantly decreased (44% and 56%) in ZD vs. ZL rats. NH was increased in ZO but not ZD rats. ALT-711 reduced ARCC and resistance (46%) in ZD rats while decreasing NH and producing similar in-stent WSS across groups. No consistent differences in RAGE or TGF-β expression were observed in arterial segments. ALT-711 modified lectin-type oxidized LDL receptor 1 but not RAGE expression by cells on decellularized matrices. In conclusion, ALT-711 decreased ARCC, increased in-stent flow rate, and reduced NH in ZO and ZD rats through RAGE-independent pathways. The study supports an important role for AGE-induced remodeling within and downstream of stent implantation to promote enhanced NH in T2DM.

Cerebral Cortical Microvascular Rarefaction in Metabolic Syndrome is Dependent on Insulin Resistance and Loss of Nitric Oxide Bioavailability.

Chronic presentation of the MS is associated with an increased likelihood for stroke and poor stroke outcomes following occlusive cerebrovascular events. However, the physiological mechanisms contributing to compromised outcomes remain unclear, and the degree of cerebral cortical MVD may represent a central determinant of stroke outcomes. This study used the OZR model of MS and clinically relevant, chronic interventions to determine the impact on cerebral cortical microvascular rarefaction via immunohistochemistry with a parallel determination of cerebrovascular function to identify putative mechanistic contributors. OZR exhibited a progressive rarefaction (to ~80% control MVD) of the cortical microvascular networks vs. lean Zucker rats. Chronic treatment with antihypertensive agents (captopril/hydralazine) had limited effectiveness in blunting rarefaction, although treatments improving glycemic control (metformin/rosiglitazone) were superior, maintaining ~94% control MVD. Chronic treatment with the antioxidant TEMPOL severely blunted rarefaction in OZR, although this ameliorative effect was prevented by concurrent NOS inhibition. Further analyses revealed that the maintenance of glycemic control and vascular NO bioavailability were stronger predictors of cerebral cortical MVD in OZR than was prevention of hypertension, and this may have implications for chronic treatment of CVD risk under stroke-prone conditions.

Long-term phosphodiesterase 5 inhibitor administration reduces inflammatory markers and heat-shock proteins in cavernous tissue of Zucker diabetic fatty rat (ZDF/fa/fa).

Oxidative stress and nitrosative stress present in type 2 diabetes mellitus (T2DM) and metabolic syndrome (MS) induce inflammatory response in diverse tissues including cavernous tissue (CT). Heat-shock proteins (HSPs) have an important role in modulating and repairing tissue injury, although their participation in CT in T2DM is unclear. Beyond the specific action of phosphodiesterase type 5 inhibitors (PDE5i) on erectile function, it has been proposed that chronic administration of these agents improves endothelial function and ameliorates fibrotic changes. The aim of this study was to determine in CT of Zucker Diabetic Fatty (ZDF) rat, an experimental model of T2DM and MS: (1) the degree of oxidative stress and nitrosative stress; (2) the magnitude of inflammatory markers such as tumor necrosis factor-α (TNFα) and interleukin 6 (IL6); (3) immunoexpression of HSP70 and HSP27; (4) how a long-term PDE5i administration may modify these variables. For 6 months, (1) untreated ZDF; (2) ZDF+Sildenafil (Sil) and (3) control Lean Zucker Rat (LZR) received no treatment, were studied. Penises were processed for functional 'in vitro' studies, oxidative and nitrosative stress evaluation and immunohistochemistry in CT using TNFα; IL6; nitrotyrosine, HSP70 and HSP27 antibodies. ZDF+Sil presented better relaxation in corporal strips versus untreated ZDF. Furthermore, ZDF+Sil presented less lipoperoxidation in CT versus untreated ZDF. The activity of antioxidant enzymes CuZn superoxide dismutase (CuZnSOD) and glutathione peroxidase (GPx) was also reduced in untreated ZDF in CT along with a decrease in glutathione versus untreated ZDF. Nitrotyrosine expression was increased in untreated-ZDF rats versus ZDF+Sil and LZR. TNFα and IL6 were decreased in CT in ZDF+Sil versus untreated ZDF. Additionally, the expression of HSP70 and HSP27 was reduced in CT in ZDF+Sil versus untreated ZDF. In conclusion, this study provides substantial evidence supporting a protective role of a long-term therapy with Sil on CT in a recognized animal model of T2DM and MS.

Modification of the β-Adrenoceptor Stimulation Pathway in Zucker Obese and Obese Diabetic Rat Myocardium.

Although metabolic syndrome is associated with increased sympathetic activity that chronically stimulates β-adrenoceptors, the β-adrenoceptor signaling pathway has been poorly studied in this situation. We studied the β-adrenoceptor signaling pathway in Zucker lean, obese, and obese diabetic rats. Experimental, prospective study. University medical research laboratory. Adult male Zucker lean (control), obese, and obese diabetic rats. The effects of β-adrenoceptor stimulation were investigated in vitro in isolated left ventricular papillary muscles in control, obese, and obese diabetic rats. β1-, β2-, and β3-adrenoceptors and multidrug resistance-associated protein 4 were quantified by Western Blotting. Triglyceride, cholesterol, leptin, adiponectin, and C-peptide plasma concentrations were measured. Data are mean ± SD. Hyperlipidemia, high leptin, and C-peptide concentrations were observed in obese and obese diabetic strains, whereas hyperglycemia occurred only in the diabetic strain. The positive inotropic effect of isoproterenol was slightly reduced in obese rats (183% ± 11% of baseline; p = 0.003; n = 7) and markedly reduced in obese diabetic rats (137% ± 18% of baseline; p < 0.001; n = 10) when compared with control rats (210% ± 17% of baseline; n = 9). β1-adrenoceptors were down-regulated in obese (-41%; p = 0.02) and diabetic (-54%; p = 0.003) when compared with control rats, whereas β3-adrenoceptors and multidrug resistance-associated protein expression remained unchanged. Direct stimulation of adenylate cyclase with forskolin or administration of 3',5'-cyclic adenosine monophosphate suggests that subtle impairments also occurred beside the down-regulation of β1-adrenoceptor. The positive inotropic effect of β-adrenoceptor stimulation is slightly decreased in Zucker obese rats and was more markedly decreased in Zucker diabetic rats. These decreases are mainly related to β1-adrenoceptor down-regulation.

Chronic NF-κB blockade improves renal angiotensin II type 1 receptor functions and reduces blood pressure in Zucker diabetic rats.

BackgroundBoth angiotensin II type 1 receptor (AT1R) and nuclear factor-kappa B (NF-κB) play significant roles in the pathogenesis of hypertension and type 2 diabetes. However, the role of NF-κB in perpetuating renal AT1 receptors dysfunction remains unclear. The aim of the present study to determine whether blockade of NF-κB, could reverse the exaggerated renal AT1R function, reduce inflammatory state and oxidative stress, lower blood pressure in Zucker diabetic fatty (ZDF) rats.MethodsPyrrolidine dithiocarbamate (PDTC), a NF-κB inhibitor (150 mg/kg in drinking water)or vehicle was administered orally to 12-weeks-old ZDF rats and their respective control lean Zucker (LZ) rats for 4 weeks. Blood pressure was measured weekly by tail-cuff method. AT1R functions were determined by measuring diuretic and natriuretic responses to AT1R antagonist (candesartan; 10 μg/kg/min iv). The mRNA and protein levels of NF-κB, oxidative stress maker and AT1R were determined using quantitative real-time PCR and Western blotting, respectively. The NF-κB-DNA binding activity in renal cortex was measured by Electrophoretic mobility shift assay (EMSA).ResultsAs compared with LZ rats, ZDF rats had higher blood pressure, impaired natriuresis and diuresis, accompanied with higher levels of oxidative stress and inflammation. Furthermore, AT1R expression was higher in renal cortex from ZDF rats; candesartan induced natriresis and diuresis, which was augmented in ZDF rats. Treatment with PDTC lowered blood pressure and improved diuretic and natriuretic effects in ZDF rats; meanwhile, the increased oxidative stress and inflammation were reduced; the increased AT1R expression and augmented candesartan-mediated natriuresis and diuresis were recoverd in ZDF rats. Our further study investigated the mechanisms of PDTC on AT1R receptor expression. It resulted that PDTC inhibited NF-κB translocation from cytosol to nucleus, inhibited binding of NF-κB with AT1R promoter, therefore, reduced AT1R expression and function.ConclusionsOur present study indicates blockade of NF-κB, via inhibition of binding of NF-κB with AT1R promoter, reduces renal AT1R expression and function, improves oxidative stress and inflammatory/anti-inflammatory balance, therefore, lowers blood pressure and recovers renal function in ZDF rats.Electronic supplementary materialThe online version of this article (doi:10.1186/s12933-015-0239-7) contains supplementary material, which is available to authorized users.

Cardiac β-Adrenoceptor Expression Is Reduced in Zucker Diabetic Fatty Rats as Type-2 Diabetes Progresses.

ObjectivesReduced cardiac β-adrenoceptor (β-AR) expression and cardiovascular dysfunction occur in models of hyperglycemia and hypoinsulinemia. Cardiac β-AR expression in type-2 diabetes models of hyperglycemia and hyperinsulinemia, remain less clear. This study investigates cardiac β-AR expression in type-2 diabetic Zucker diabetic fatty (ZDF) rats.Methods Ex vivo biodistribution experiments with [3H]CGP12177 were performed in Zucker lean (ZL) and ZDF rats at 10 and 16 weeks of age as diabetes develops. Blood glucose, body mass, and diet consumption were measured. Western blotting of β-AR subtypes was completed in parallel. Echocardiography was performed at 10 and 16 weeks to assess systolic and diastolic function. Fasted plasma insulin, free fatty acids (FFA), leptin and fed-state insulin were also measured.ResultsAt 10 weeks, myocardial [3H]CGP12177 was normal in hyperglycemic ZDF (17±4.1mM) compared to ZL, but reduced 16-25% at 16 weeks of age as diabetes and hyperglycemia (22±2.4mM) progressed. Reduced β-AR expression not apparent at 10 weeks also developed by 16 weeks of age in ZDF brown adipose tissue. In the heart, Western blotting at 10 weeks indicated normal β1-AR (98±9%), reduced β2-AR (76±10%), and elevated β3-AR (108±6). At 16 weeks, β1-AR expression became reduced (69±16%), β2-AR expression decreased further (68±14%), and β3-AR remained elevated, similar to 10 weeks (112±9%). While HR was reduced at 10 and 16 weeks in ZDF rats, no significant changes were observed in diastolic or systolic function.ConclusionsCardiac β-AR are reduced over 6 weeks of sustained hyperglycemia in type-2 diabetic ZDF rats. This indicates cardiac [3H]CGP12177 retention and β1- and β2-AR expression are inversely correlated with the progression of type-2 diabetes.

C-Peptide-based assessment of insulin secretion in the Zucker Fatty rat: a modelistic study.

A C-peptide-based assessment of β-cell function was performed here in the Zucker fatty rat, a suitable animal model of human metabolic syndrome. To this aim, a 90-min intravenous glucose tolerance test (IVGTT) was performed in seven Zucker fatty rats (ZFR), 7-to-9week-old, and seven age-matched Zucker lean rats (ZLR). The minimal model of C-peptide (CPMM), originally introduced for humans, was adapted to Zucker rats and then applied to interpret IVGTT data. For a comprehensive evaluation of glucose tolerance in ZFR, CPMM was applied in combination with the minimal model of glucose kinetics (GKMM). Our results showed that the present CPMM-based interpretation of data is able to: 1) provide a suitable fit of C-Peptide data; 2) achieve a satisfactory estimation of parameters of interest 3) quantify both insulin secretion by estimating the time course of pre-hepatic secretion rate, SR(t), and total insulin secretion, TIS, and pancreatic sensitivity by means of three specific indexes of β-cell responsiveness to glucose stimulus (first-phase, Ф1, second-phase, Ф2, and steady-state, Фss, never assessed in Zucker rats before; 4) detect the significant enhancement of insulin secretion in the ZFR, in face of a severe insulin-resistant state, previously observed only using a purely experimental approach. Thus, the methodology presented here represents a reliable tool to assess β-cell function in the Zucker rat, and opens new possibilities for the quantification of further processes involved in glucose homeostasis such as the hepatic insulin degradation.

Preliminary evaluation of β3-adrenoceptor agonist-induced 18F-FDG metabolic activity of brown adipose tissue in obese Zucker rat

BackgroundWe have investigated β3-adrenoceptor agonist mediated brown adipose tissue (BAT) activation using 18F-FDG PET/CT in Zucker lean (ZL) and obese (ZF) rats. Methods18F-FDG was injected into ZL and ZF rats pretreated with saline or agonist CL316,243 for scans. 18F-FDG metabolic activity was computed as standard uptake values. ResultsCL316,243 in ZL activated BAT up to 4-fold compared to saline, while ZF BAT was only up by 2 fold. The decreased activation was consistent with lower β3-adrenoceptor levels in ZF rats. ConclusionsThe genetically modified ZL and ZF rats may provide a useful rat model to evaluate the significance of β3-adrenoceptor agonist-induced BAT activation in obesity.

Matrix metalloproteinase-9 expression is enhanced in renal parietal epithelial cells of zucker diabetic Fatty rats and is induced by albumin in in vitro primary parietal cell culture.

As a subfamily of matrix metalloproteinases (MMPs), gelatinases including MMP-2 and MMP-9 play an important role in remodeling and homeostasis of the extracellular matrix. However, conflicting results have been reported regarding their expression level and activity in the diabetic kidney. This study investigated whether and how MMP-9 expression and activity were changed in glomerular epithelial cells upon albumin overload. In situ zymography, immunostaining and Western blot for renal MMP gelatinolytic activity and MMP-9 protein expression were performed in Zucker lean and Zucker diabetic rats. Confocal microscopy revealed a focal increase in gelatinase activity and MMP-9 protein in the glomeruli of diabetic rats. Increased glomerular MMP-9 staining was mainly observed in hyperplastic parietal epithelial cells (PECs) expressing claudin-1 in the diabetic kidneys. Interestingly, increased parietal MMP-9 was often accompanied by decreased staining for podocyte markers (nephrin and podocalyxin) in the sclerotic area of affected glomeruli in diabetic rats. Additionally, urinary excretion of podocyte marker proteins was significantly increased in association with the levels of MMP-9 and albumin in the urine of diabetic animals. To evaluate the direct effect of albumin on expression and activity of MMP-9, primary cultured rat glomerular PECs were incubated with rat serum albumin (0.25 - 1 mg/ml) for 24 - 48 hrs. MMP-9 mRNA levels were significantly increased following albumin treatment. Meanwhile, albumin administration resulted in a dose-dependent increase in MMP-9 protein and activity in culture supernatants of PECs. Moreover, albumin activated p44/42 mitogen-activated protein kinase (MAPK) in PECs. Inhibition of p44/42 MAPK suppressed albumin-induced MMP-9 secretion from glomerular PECs. Taken together, we have demonstrated that an up-regulation of MMP-9 in activated parietal epithelium is associated with a loss of adjacent podocytes in progressive diabetic nephropathy. Albumin overload may induce MMP-9 expression and secretion by PECs via the activation of p44/42 MAPK pathway.

Effects of habitual exercise and dietary restriction on intrahepatic and periepididymal fat accumulation in Zucker fatty rats.

BackgroundHabitual exercise and dietary restriction are commonly recommended to prevent or ameliorate obesity and lifestyle-related diseases, including fatty liver. This study investigated the effects of habitual exercise and dietary restriction on hepatic triglyceride (TG) levels, serum leptin levels, and histological adipocyte size in periepididymal adipose tissue from Zucker fatty (ZF) rats.MethodsSix-week-old male ZF rats were randomly assigned to one of three groups: sedentary (Sed), sedentary and dietary restriction (Sed + DR), and training and dietary restriction (Tr + DR). Male Zucker lean (L) rats were used as control animals. All rats had access to water and the allowed quantity of food ad libitum. The rats in the Sed + DR and Tr + DR groups were fed a 30% restricted diet, while those in the Tr + DR group exercised voluntarily on a wheel ergometer. After 12 weeks, the rats were sacrificed for a histological examination of their liver and periepididymal adipose tissue. Hepatic and serum TG, serum total cholesterol, glutamic-oxaloacetic transaminase, glutamic-pyruvic transaminase, free fatty acid, and leptin levels were also measured.ResultsThe hepatic TG levels were significantly higher in the Sed + DR group than in the L (P < 0.001) and Sed (P < 0.05) groups. By contrast, the hepatic TG levels in the Tr + DR group were significantly lower than those in the Sed (P < 0.05) and Sed + DR (P < 0.001) groups, but not significantly different from the L group values. The periepididymal adipocytes were significantly larger in the Sed, Sed + DR, and Tr + DR groups than in the L group (P < 0.001) and were significantly smaller in the Tr + DR group compared to the Sed and Sed + DR groups (P < 0.001).ConclusionsOur results suggest a relationship between lipid metabolism and the size of adipose cells in ZF rats. Exercising plays an important role in decreasing hepatic TG levels, serum leptin levels, and the size of adipose cells.

Differences in the Responses to Chronic Rapamycin Treatment by Healthy and Insulin Resistant Rats.

The immunosuppressant rapamycin (Rap) inhibits mTOR Complex 1 and promotes longevity. However, Rap also induces type 2 diabetes (T2DM). Since DM is an independent predictor for cardiovascular disease, we investigated whether chronic Rap treatment that exacerbates diabetes modulates cardiac pathology differently in healthy and insulin resistant individuals. Young (8‐20 weeks) healthy Zucker lean (ZL) and insulin resistant Zucker obese (ZO) rats were subjected to 12‐week Rap treatment via subcutaneous implantation of Rap pellets delivering Rap at a concentration of 750μg/kg/day. Rap significantly suppressed body weight, heart weight, fasting plasma levels of cholesterol, triglycerides, and LDL in ZO rats, but worsened diabetes as indicated by severe hyperglycemia, polydipsia and polyuria (p&lt;0.05). Echocardiography showed that 14‐week old ZO rats exhibited diastolic dysfunction evidenced by decreases in the tissue doppler E'/A' ratio, mitral inflow propagation velocity (Vp), and increases in LV filling pressure (E/E' and E/Vp ratios), isovolumic relaxation time (IVRT) and myocardial performance index (Tei index of global cardiac function) compared to age‐matched ZL rats(p&lt;0.05). With the exception of IVRT, these abnormalities were improved in ZO rats treated for 6 weeks with Rap. However, an additional 6 weeks of Rap treatment reversed this effect. Histopathology showed that Rap induced significant cardiomyofibril disarray in both ZL and ZO rats (p&lt;0.05), damaged the healthy circular morphology of pancreatic islets in ZL and ZO rats and reduced fibrosis in ZO rats, but not in ZL rats. Thus, the heart and pancreas of healthy and insulin resistant rats respond differently to chronic Rap treatment.

Upregulation of Orexin Receptor in Paraventricular Nucleus Promotes Sympathetic Outflow Through Non‐selective Cation Channel in Obesity

AbstractElevated sympathetic outflow contributes to hypertension in obesity. Orexins importantly regulates autonomic function. Presently we determined the role of orexin in the paraventricular (PVN) nucleus of hypothalamus in controlling sympathetic outflow in obese Zucker rats (OZRs) and lean Zucker rats (LZRs). Orexin A microinjection into PVN significiantly dose‐dependently elevated arterial blood pressure (ABP) and renal sympathetic nerve activity (RSNA) manner in anesthetized OZRs than LZRs, which eliminated by SB‐334867, orexin receptor 1 receptor (OX1R) antagonist, but not TCS‐OX2‐29, OX2R antagonist. Furthermore, SB‐334867 reduced basal ABP and RSNA in OZRs but not LZRs. Compared with LZRs, OX1R expression in PVN was significantly higher in OZRs, while no difference for OX2R. OX1R immunoreactivity was positive in retrogradely labeled PVN‐spinal neurons. Compared with LZRs, the basal firing rate in the PVN‐spinal neurons was higher in OZRs, and orexin A excited firing activity in PVN‐spinal neurons in OZRs, which eliminated by SB334867. SB334867 also decreased basal firing activity of these neurons in OZRs. In addition, orexin A induced larger currents in PVN spinal neurons in OZRs. These data suggest that upregulation of OX1R in the PVN promotes hyperactivity of PVN presympathetic neurons and sympathetic outflow in obesity.This work was supported by National Institutes of Health (Grants MH096086 to D.‐P. L.) and National Natural Sciences Foundation of China (31271223 and 31071002).

Effects of Chronic Stress on Pancreatic Beta Cell Density in Obese and Lean Zucker Rats

Chronic stress has been implicated as a possible contributing factor to the onset of Type 2 Diabetes Mellitus through its negative effects on the insulin producing β cells of the pancreas. The objective of this study was to evaluate a model of chronic stress and the metabolic syndrome on beta cell density in rats. Obese (OZR) and lean Zucker rats (LZR) were randomly divided into stress (OZR‐S, n=6; LZR‐S, n=6) and non‐stress (OZR‐NS, n=3; LZR‐NS, n=3). Stress included bath, damp bedding, no bedding, cage tilt, altered light cycles, and cage‐switching for 7 hours/day, 5 days/week for 8 weeks after which animals were euthanized. Pancreases were harvested and mounted on cork using OTC freezing medium. Pancreas sections of 7µm thickness were cut and collected on slides then stained using Alexa‐Fluor 546 targeting primary insulin antibodies and DAPI. Slides were then imaged using the Zeiss LSM 510 Confocal microscope and Zeiss computer software. The insulin positive area of the stained islets was measured using the Image J program.The images of stained cells and islets were merged and the number of beta cells per islet recorded. A two‐way ANOVA was used to compare the beta cell density (beta cell/µm2 insulin positive area) among groups with significance set at p&lt;.05. There was a significant main effect of stress with stressed animals having a lower beta cell density compared with non‐stressed (Stressed: 0.00566±.001; Non‐Stressed: 0.00861±.001µm2). No differences were observed between OZR and LZR. These results indicate that 8 weeks of chronic stress caused beta cell density to be reduced in both OZR and LZR and this was not affected further by the metabolic condition of the animals.

Therapeutic Potential of S43126 to Treat Select Patients with Type 2 Diabetes and Hypertension

Novel therapeutic agents with reduced side‐effect profile are needed to treat type 2 diabetes. The objective of this study is to highlight the potential of a novel imidazoline compound S43126 as a future antidiabetic drug. We hypothesize that S43126 can exert beneficial effects in type 2 diabetes by a mechanism involving insulin release and insulin sensitization. Rat tail arteries were treated in a bath system with S43126 and other compounds to determine the contractile response to these agents. Control Zucker lean rats (ZLRs) and Zucker diabetic rats (ZDRs) were treated with S43126 or moxonidine for 2 weeks, and then plasma glucose and blood pressure were measured. Insulin release by mouse islets in response to varying doses of S43126 was determined. Western blot was used to determine the effect of S43126 on PKB phosphorylation. S43126 did not contract rat tail artery, but lowered blood glucose in ZDR by 31% relative to control, with no significant effect in ZLR. S43126 significantly reduce blood pressure in ZDR only. S43126 caused a dose‐dependent insulin release of up to 4 fold from mouse islet cells, only under conditions of high glucose. S43126 increased PKB phosphorylation which was blocked by efaroxan. These data suggests that S43126 decrease blood glucose by a mechanism involving insulin release, sensitization, or both. S43126 should be further studied as a possible agent to treat some patients who have type 2 diabetes and hypertension.

COX-2 is involved in vascular oxidative stress and endothelial dysfunction of renal interlobar arteries from obese Zucker rats

Obesity is related to vascular dysfunction through inflammation and oxidative stress and it has been identified as a risk factor for chronic renal disease. In the present study, we assessed the specific relationships among reactive oxygen species (ROS), cyclooxygenase 2 (COX-2), and endothelial dysfunction in renal interlobar arteries from a genetic model of obesity/insulin resistance, the obese Zucker rats (OZR). Relaxations to acetylcholine (ACh) were significantly reduced in renal arteries from OZR compared to their counterpart, the lean Zucker rat (LZR), suggesting endothelial dysfunction. Blockade of COX with indomethacin and with the selective blocker of COX-2 restored the relaxations to ACh in obese rats. Selective blockade of the TXA2/PGH2 (TP) receptor enhanced ACh relaxations only in OZR, while inhibition of the prostacyclin (PGI2) receptor (IP) enhanced basal tone and inhibited ACh vasodilator responses only in LZR. Basal production of superoxide was increased in arteries of OZR and involved NADPH and xanthine oxidase activation and NOS uncoupling. Under conditions of NOS blockade, ACh induced vasoconstriction and increased ROS generation that were augmented in arteries from OZR and blunted by COX-2 inhibition and by the ROS scavenger tempol. Hydrogen peroxide (H2O2) evoked both endothelium- and vascular smooth muscle (VSM)-dependent contractions, as well as ROS generation that was reduced by COX-2 inhibition. In addition, COX-2 expression was enhanced in both VSM and endothelium of renal arteries from OZR. These results suggest that increased COX-2-dependent vasoconstriction contributes to renal endothelial dysfunction through enhanced (ROS) generation in obesity. COX-2 activity is in turn upregulated by ROS.

A Diet High in Protein Reduces Weight Gain, Food Intake and Liver Weight in Obese Zucker Rats

It has become a challenge to find effective treatments and preventive strategies to reduce obesity and diabetes (T2DM). There are several approaches to treating these diseases, including nutrition therapy. Diets high in protein are linked with weight reduction and improved insulin resistance. Therefore, the objective of this study was to examine the effects of a long‐term, high protein (pro) diet (40%) vs a moderate pro diet (20%) on body composition and metabolism using a genetic model of obesity/T2DM. Male, lean (L) and obese (O) Zucker rats (n = 8‐10 per group) were housed 2/cage and placed in one of four groups: L20, L40, O20 or O40. Animals were provided ad libitum access to diet and water for 12 weeks. At 12 weeks, animals were fasted for 8 hours, then trunk blood and tissues were collected. L had lower food intake (P &lt; 0.05) than O, and O40 had significantly lower food intake (P &lt; 0.05) than O20. Animals fed 40% pro had significantly lower weight gain (P &lt; 0.05) than those fed 20% pro. L had more muscle mass and lower fat mass than O (P &lt; 0.05). However, L40 had significantly lower fat mass than L20. O40 had lower liver weights (P &lt; 0.05) than O20. There was no difference in fasting glucose and O had higher fasting insulin. Fasting free fatty acids were higher in animals fed the 20% pro diet. There was no difference in basal phosphorylation of Akt, AMPK, mTOR or 4E‐BP1. There was no difference in basal BCAA between L20 and O20. L40 and O40 had significantly higher basal levels of BCAA (P &lt; 0.05). We conclude that higher protein diets have the potential to reduce weight gain and alter metabolism in obese rats. Funded by Arkansas Biosciences Institute.

Tissue‐Specific Proportions of Phylloquinone to Menaquinone‐4 Concentrations Differ in Response to Dietary Phylloquinone Manipulation in Lean Male Zucker Rats

Phylloquinone (PK) and menaquinone (MK) are naturally-occurring forms of vitamin K (VK).There is selective tissue distribution and conversion of dietary PK to MK4, providing indirect evidence of un...

Attenuation of Post‐Trauma Hyperglycemia Prevents Acute Kidney Injury in Obese Rats

Traumatic injury is one of the leading causes of death in the United States, and obese patients have an increased risk of developing post-trauma acute kidney injury (AKI). Hyperglycemia after trauma is correlated with worse outcomes, but whether it contributes to AKI in the context of obesity is not known. We hypothesized that blunting the hyperglycemic response would prevent AKI in obese rats. Lower-limb orthopedic trauma was induced in lean (LZR) and obese (OZR) Zucker rats (12wk) by fibula fracture, soft tissue injury, and bone component injection. Plasma glucose levels were measured for five hours after trauma, and glomerular filtration rate (GFR) and plasma interleukin-6 (IL-6) were measured the day after trauma and in non-trauma control rats (all groups n蠅6). OZR had higher peak glucose levels after trauma than LZR (275±19 vs 167±13 mg/dL; p<.05) as well as prolonged hyperglycemia. Treatment of the OZR after trauma with glucagon-like peptide-1 (GLP-1), an incretin with insulinotropic effects (3μg/kg/hr IV), reduced peak glucose levels to 152±12 mg/dL (p<.05). In LZR with trauma, GFR did not decrease as compared to controls (1.44±0.1 vs 1.67±0.2 mL/min/g), while OZR with trauma had significantly decreased GFR as compared to controls (0.96±0.1 vs 1.92±0.1 mL/min/g; p<.05). Treatment with GLP-1 in OZR prevented this decrease (1.98 mL/min/g; p<.05). IL-6 levels were increased in LZR with trauma as compared to controls (400±114 vs 77±12 pg/dL; p<.05), while OZR with trauma had a larger increase (3834±1099 vs 75±6 pg/dL for OZR control; p<.05), and GLP-1 treatment decreased IL-6 levels (269±15 pg/dL; p<.05). These data suggest that acute hyperglycemia contributes to increased inflammation and AKI development after trauma in obesity.

Effects of Acute and Chronic Hyperglycemia on Lung Capillary Permeability

Hyperglycemia is correlated with increased vascular oxidative stress and increased vascular permeability. The role of acute and chronic hyperglycemia in affecting lung endothelial permeability is unclear in a type 2 diabetes setting. Lung capillary filtration coefficient (Kf) was measured in the isolated lung of lean Zucker (LZ) and obese Zucker rats (OZ). We hypothesized obesity increases lung vascular permeability through chronic hyperglycemia. OZ had impaired glucose and insulin tolerance which was associated with elevated lung Kf (19.4 ± 3 ml/mmHg/g/min) as compared to LZ (11.4 ± 2 ml/mmHg/g/min). In a separate experiment, OZ were subjected to 4 weeks of Metformin treatment (300 mg/kg/day orally) to improve insulin sensitivity. Metformin treatment improved oral glucose tolerance, insulin sensitivity, and vascular oxidative stress, and this was associated with improved baseline lung Kf (11.5 ± 1 ml/mmHg/g/min) as compared to OZ control animals. To examine the role of acute hyperglycemia in lung permeability, lungs from LZ and OZ were subjected to 30 minutes of an elevated glucose concentration (550 mg/dl). Acute hyperglycemia had no effect in OZ but increased lung Kf in LZ, which was ameliorated with acute antioxidant treatment (apocynin, 3mM) added to the lung perfusion solution. These data suggest that the chronic hyperglycemia in obesity can exacerbate lung vascular permeability, possibly through oxidative stress, and may blunt any further alterations in Kf during acute episodes hyperglycemia. This warrants further investigation into the use of antioxidants in the treatment of diabetic and acute hyperglycemic-induced lung hyperpermeability.