Treatment of cardiovascular dysfunction associated with the metabolic syndrome and type 2 diabetes

Multimodal Comparison of Diabetic Neuropathy in Aged Streptozotocin-Treated Sprague-Dawley and Zucker Diabetic Fatty Rats

The development and progression of diabetic polyneuropathy (DPN) are due to multiple mechanisms. The creation of reliable animal models of DPN has been challenging and this issue has not yet been solved. However, despite some recognized differences from humans, most of the current knowledge on the pathogenesis of DPN relies on results achieved using rodent animal models. The simplest experimental DPN model reproduces type 1 diabetes, induced by massive chemical destruction of pancreatic beta cells with streptozotocin (STZ). Spontaneous/transgenic models of diabetes are less frequently used, mostly because they are less predictable in clinical course, more expensive, and require a variable time to achieve homogeneous metabolic conditions. Among them, Zucker diabetic fatty (ZDF) rats represent a typical type 2 diabetes model. Both STZ-induced and ZDF rats have been extensively used, but only very few studies have compared the long-term similarities and differences existing between these two models. Moreover, inconsistencies have been reported regarding several aspects of short-term in vivo studies using these models. In this study, we compared the long-term course of DPN in STZ-treated Sprague-Dawley and ZDF rats with a multimodal set of readout measures.

Endothelium dysfunction in hind limb arteries of male Zucker Diabetic-Sprague Dawley rats

Endothelium dysfunction produces peripheral vascular disease comorbidities in type 2 diabetes, including hypertension, and critical limb ischemia. In this study we aimed to test endothelial dysfunction, the vasodilator effects of a proteinase-activated receptor 2 (PAR2) agonist (2fLIGRLO), and thromboxane A₂ synthase inhibitor (ozagrel) on PAR2 vasodilation in hind limb arteries ex vivo, using Zucker Diabetic-Sprague Dawley (ZDSD) rats, a model of type 2 diabetes. Male Sprague Dawley rats (SD) and ZDSD were fed a high-fat content 'Western diet' from 16 to 20 weeks of age (wks) then fed a standard laboratory diet. We identified diabetic ZDSD rats by two consecutive blood glucose measurements > 12.5 mM, based on weekly monitoring. We used acetylcholine, 2fLIGRLO, and nitroprusside with wire-myograph methods to compare relaxations of femoral, and saphenous arteries from diabetic ZDSD (21-23 wks) to age-matched normoglycemic SD. All arteries showed evidence of endothelium dysfunction using acetylcholine (reduced maximum relaxations, reduced sensitivity), and higher sensitivities to 2fLIGRLO, and nitroprusside in ZDSD vs SD. Ozagrel treatment of ZDSD distal segments, and end-branches of saphenous arteries decreased their sensitivities to 2fLIGRLO. We tested aortas for altered expression of endothelium-specific gene targets using PCR array and qPCR. PAR2, and placental growth factor gene transcripts were 1.5, and 4-times higher in ZDSD than SD aortas. Hind limb arteries of ZDSD exhibit endothelium dysfunction having less GPCR agonist induced vasodilation by endothelial NO-release. Different expression of several endothelial genes in ZDSD vs SD aortas, including PAR2, suggests altered inflammatory, and angiogenesis signaling pathways in the endothelium of ZDSD.

The role of melatonin in the onset and progression of type 3 diabetes

Alzheimer’s disease (AD) is defined by the excessive accumulation of toxic peptides, such as beta amyloid (Aβ) plaques and intracellular neurofibrillary tangles (NFT). The risk factors associated with AD include genetic mutations, aging, insulin resistance, and oxidative stress. To date, several studies that have demonstrated an association between AD and diabetes have revealed that the common risk factors include insulin resistance, sleep disturbances, blood brain barrier (BBB) disruption, and altered glucose homeostasis. Many researchers have discovered that there are mechanisms common to both diabetes and AD. AD that results from insulin resistance in the brain is termed “type 3 diabetes”. Melatonin synthesized by the pineal gland is known to contribute to circadian rhythms, insulin resistance, protection of the BBB, and cell survival mechanisms. Here, we review the relationship between melatonin and type 3 diabetes, and suggest that melatonin might regulate the risk factors for type 3 diabetes. We suggest that melatonin is crucial for attenuating the onset of type 3 diabetes by intervening in Aβ accumulation, insulin resistance, glucose metabolism, and BBB permeability.

Effect of enalapril maleate on ghrelin levels in metabolic syndrome in rats

We have explored how enalapril affects ghrelin levels in serum and renal tissues of rats with fructose-induced MetS, using 5-week-old Wistar albino male rats weighing 220 ± 20 g. They divided into 5 groups: (i) control (CT), no fructose supplement fed on standard rat pellet and tap water for 60 days, (ii) metabolic syndrome (MetS) fed with 10% fructose for 60 days, (iii) rats after metabolic syndrome developed treated with enalapril over 30 days (MetS+E30), (iv) rats in which only enalapril was administered for 60 days (E60), and (v) MetS-treated with enalapril for 60 days (MetS+E60). Enalapril maleate was given at 20mg/kg per day by gavage. Fasting serum insulin, uric acid, triglyceride, low-density lipoprotein cholesterol and total cholesterol levels were significantly higher, and the amount of high density lipoprotein cholesterol, and acylated and desacyl ghrelin levels was significantly lower in the MetS groups. Ghrelins were significantly lower in all 3 groups, which were administered enalapril than that of MetS and the control group. Immunohistochemical staining showed that the density of ghrelin was parallel to the serum levels of the peptide. Ghrelin immunoreactivity in the kidneys was of moderate density in the distal and collecting tubules, mild density in the proximal tubule and glomeruli, whereas the density decreased in the MetS group and other enalapril-treated groups. In conclusion, ghrelin levels in MetS groups were significantly lower than control group, and thus Enalapril treatment improves components of MetS and has direct effects on serum ghrelin levels that are independent of MetS.

Cardiovascular, metabolic, and coronary dysfunction in high-fat-fed obesity-resistant/prone rats

OBJECTIVE

Obesity is a global epidemic leading to several comorbidities including diabetes and cardiovascular disease. The hypothesis that the genetic background of the obesity-prone rat (OP) predisposes to physiologic, metabolic, and microvascular dysfunction which is exacerbated by a diet high in saturated fats was tested.

METHODS

Male OP and obesity-resistant (OR) rats were fed either a diet containing 10% (chow) or 45% kcal fat (HF) for 42 weeks.

RESULTS

Weight of OP rats was greater than OR rats by 8 weeks on both diets. Blood pressure was increased in OP rats on chow and further augmented by HF diet compared to OR rats on similar diets. In contrast to weight and blood pressure, glucose clearance was similar in OR and OP rats on chow and impaired in both models on HF diet. Relaxation to acetylcholine was attenuated in OP rats compared to OR rats by 8 weeks and remained reduced throughout the study. A longer period of time was required to observe vascular dysfunction in HF-fed OR rats.

CONCLUSIONS

When compared to OR rats, OP rats are prone to develop not only greater obesity but also hypertension and vascular dysfunction on a normal diet which is further augmented with HF diet.

Characterization of diabetic neuropathy in the Zucker diabetic Sprague-Dawley rat: a new animal model for type 2 diabetes

Recently a new rat model for type 2 diabetes the Zucker diabetic Sprague-Dawley (ZDSD/Pco) was created. In this study we sought to characterize the development of diabetic neuropathy in ZDSD rats using age-matched Sprague-Dawley rats as a control. Rats were examined at 34 weeks of age 12 weeks after the onset of hyperglycemia in ZDSD rats. At this time ZDSD rats were severely insulin resistant with slowing of both motor and sensory nerve conduction velocities. ZDSD rats also had fatty livers, elevated serum free fatty acids, triglycerides, and cholesterol, and elevated sciatic nerve nitrotyrosine levels. The corneas of ZDSD rats exhibited a decrease in subbasal epithelial corneal nerves and sensitivity. ZDSD rats were hypoalgesic but intraepidermal nerve fibers in the skin of the hindpaw were normal compared to Sprague-Dawley rats. However, the number of Langerhans cells was decreased. Vascular reactivity of epineurial arterioles, blood vessels that provide circulation to the sciatic nerve, to acetylcholine and calcitonin gene-related peptide was impaired in ZDSD rats. These data indicate that ZDSD rats develop many of the neural complications associated with type 2 diabetes and are a good animal model for preclinical investigations of drug development for diabetic neuropathy.

Progression and reversal of coronary and mesenteric vascular dysfunction associated with obesity

OBJECTIVE

The purpose of this study was to examine progression and reversal of microvascular complications when rats were fed a high fat diet.

METHODS

Sprague-Dawley rats 10 weeks of age were fed a diet containing 45% kcal fat for up to 32 weeks. Blood pressure and heart rate was measured by telemetry. Vascular reactivity of aorta and small coronary and mesenteric vessels was determined after 8, 16, 24, and 32 weeks on diet.

RESULTS

There was a modest increase in weight and blood pressure in high fat fed rats. Sodium nitroprusside (SNP)-induced relaxation of coronary arteries was potentiated after 8 weeks on high fat diet, however, this enhanced response was not observed after 16, 24, or 32 weeks of diet. Acetylcholine (Ach) mediated relaxation was attenuated after 16, 24, and 32 weeks of high fat diet in coronary arteries; however, in aorta and mesenteric arteries, Ach-mediated response was not altered until 32 weeks on high fat diet. Reversing the high fat diet for 8 weeks resulted in partial recovery of metabolic parameters; however endothelial function in coronary arteries remained impaired.

CONCLUSIONS

These studies indicate that high fat diet promotes progressive impairment of coronary vascular function that is difficult to reverse.

Most appropriate animal models to study the efficacy of statins: a systematic review

BACKGROUND

In animal models and clinical trials, statins are reported as effective in reducing cholesterol levels and lowering the risk of cardiovascular diseases. We have aggregated the findings in animal models - mice, rats and rabbits - using the technique of systematic review and meta-analysis to highlight differences in the efficacy of statins.

MATERIALS AND METHODS

We searched Medline and Embase. After examining all eligible articles, we extracted results about total cholesterol and other blood parameters, blood pressure, myocardial infarction and survival. Weighted and standard mean difference random effects meta-analysis was used to measure overall efficacy in prespecified species, strains and subgroups.

RESULTS

We included in systematic review 161 animal studies and we analysed 120 studies, accounting for 2432 animals. Statins lowered the total cholesterol across all species, although with large differences in the effect size: -30% in rabbits, -20% in mice and -10% in rats. The reduction was larger in animals fed on a high-cholesterol diet. Statins reduced infarct volume but did not consistently reduce the blood pressure or effect the overall survival. Few studies considered strains at high risk of cardiovascular diseases or hard outcomes.

CONCLUSIONS

Although statins showed substantial efficacy in animal models, few preclinical data considered conditions mimicking human pathologies for which the drugs are clinically indicated and utilized. The empirical finding that statins are more effective in lowering cholesterol derived from an external source (i.e. diet) conflicts with statin's supposed primary mechanism of action.

Prevention of hyperglycemic signal pathways in metabolic syndrome carotid artery of rats

Obesity is the major risk factor for metabolic syndrome and atherosclerotic cardiocerebrovascular diseases and induces insulin resistance characterized by a dysfunction of insulin to activate insulin receptor /insulin receptor substrate 1(IRS-1)/phosphoinositide 3-kinase (PI3K)/Akt pathway. Zucker fatty rats (8 weeks) were treated with vehicle (0.5 % methyl cellulose in physiological saline, p.o.), amlodipine (3 mg/kg/day, p.o.), atorvastatin (10 mg/kg/day, p.o.), or the combination of amlodipine plus atorvastatin (3 + 10 mg/kg/day, p.o.) for 28 days, and anti-insulin-like growth factor 1 (IGF-1)/IRS-1/PI3K/Akt pathways were evaluated. Our present immunohistochemical study first demonstrated that a combination of amlodipine plus atorvastatin treatment prevented an arteriosclerotic process compared to the single treatment with amlodipine or atorvastatin with strong recoveries of pTyr IRS-1, pPI3K, and pAkt expressions and with remarkable restraints of IGF-1 and pSer IRS-1. As a result, combination therapy with amlodipine plus atorvastatin showed a strong synergistic effect to prevent atherosclerotic processes. The present study newly suggests a synergistic benefit of combination therapy with amlodipine plus atorvastatin for strong prevention of atherosclerotic processes, which could reduce the clinical risk of cerebrovascular events for obesity patients.

Preserved endothelium-dependent dilatation of the coronary microvasculature at the early phase of diabetes mellitus despite the increased oxidative stress and depressed cardiac mechanical function ex vivo

Background

There has been accumulating evidence associating diabetes mellitus and cardiovascular dysfunctions. However, most of the studies are focused on the late stages of diabetes and on the function of large arteries. This study aimed at characterizing the effects of the early phase of diabetes mellitus on the cardiac and vascular function with focus on the intact coronary microvasculature and the oxidative stress involved.

Materials and methods

Zucker diabetic fatty rats and their lean littermates fed with standard diet A04 (Safe) were studied at the 11th week of age. Biochemical parameters such as glucose, insulin and triglycerides levels as well as their oxidative stress status were measured. Their hearts were perfused ex vivo according to Langendorff and their cardiac activity and coronary microvascular reactivity were evaluated.

Results

Zucker fatty rats already exhibited a diabetic state at this age as demonstrated by the elevated levels of plasma glucose, insulin, glycated hemoglobin and triglycerides. The ex vivo perfusion of their hearts revealed a decreased cardiac mechanical function and coronary flow. This was accompanied by an increase in the overall oxidative stress of the organs. However, estimation of the active form of endothelial nitric oxide synthase and coronary reactivity indicated a preserved function of the coronary microvessels at this phase of the disease. Diabetes affected also the cardiac membrane phospholipid fatty acid composition by increasing the arachidonic acid and n-3 polyunsaturated fatty acids levels.

Conclusions

The presence of diabetes, even at its beginning, significantly increased the overall oxidative stress of the organs resulting to decreased cardiac mechanical activity ex vivo. However, adaptations were adopted at this early phase of the disease regarding the preserved coronary microvascular reactivity and the associated cardiac phospholipid composition in order to provide a certain protection to the heart.

Study of the effects of monacolin k and other constituents of red yeast rice on obesity, insulin-resistance, hyperlipidemia, and nonalcoholic steatohepatitis using a mouse model of metabolic syndrome

Purpose. Nonalcoholic fatty liver disease (NAFLD) is a progressive and intractable disease associated with metabolic syndrome. Red yeast rice (RYR) contains monacolin K, a potent inhibitor of HMG-CoA reductase, and its consumption decreases cholesterol and triglyceride levels. We examined the efficacy of RYR constituents using a novel metabolic syndrome-NAFLD mouse model (MSG mice). Methods. Two types of RYR grown under different culture conditions were used. 1P-DU contained only 0.002 g/100 g of monacolin K, whereas 3P-D1 contained 0.131 g/100 g. MSG mice were divided into three groups: control (C) group fed standard food, RYR-C group fed standard food with 1% 1P-DU, and RYR-M group fed standard food with 1% 3P-D1. Mice were examined from 12 to 24 weeks of age. Results. Serum insulin, leptin, and liver damage as well as macrophage aggregation in visceral fat in RYR-C and RYR-M groups were lower than those in C group. The serum adiponectin levels in RYR-C group were significantly higher than those in RYR-M and C groups. Conclusions. RYR was effective against obesity-related inflammation, insulin resistance, and NAFLD in MSG mice irrespective of monacolin K levels. GABA and various peptides produced during fermentation were determined as the active constituents of RYR.

Murine models for pharmacological studies of the metabolic syndrome

Metabolic syndrome has been described as the association of insulin resistance, hypertension, hyperlipidemia and obesity. Its prevalence increased dramatically, mainly in developed countries. Animal models are essential to understand the pathophysiology of this syndrome. This review presents the murine models of metabolic syndrome the most often used in pharmacological studies. The most common metabolic syndrome models exhibit a non-functional leptin pathway, or metabolic disorders induced by high fat diets. In a first part, and after a short introduction on leptin, its receptor and mechanism of action, we provide a detailed description of each model: SHROB, SHHF, JCR:LA-cp, Zucker, ZDF, Wistar Ottawa Karlsburg W, and Otsuka Long-Evans Tokushima Fatty rats, ob/ob, db/db, agouti yellow and Mc4R KO mice. The second part of this review is dedicated to metabolic syndrome models obtained by high fat feeding.

Attenuation of renovascular damage in Zucker diabetic fatty rat by NWT-03, an egg protein hydrolysate with ACE- and DPP4-inhibitory Activity

Background

Dipeptidyl peptidase 4 (DPP4) and angiotensin-converting enzyme (ACE) are important target enzymes in glycemic control and renovascular protection. Here, we studied the effect of NWT-03, an egg protein hydrolysate with DPP4- and ACE-inhibitory activity, on renovascular damage in Zucker diabetic fatty (ZDF) rats. Comparisons were made to rats treated with vildagliptin (VIL), included as a positive control for the effect of DPP4 inhibition.

Methods

ZDF rats received NWT-03 (1 g/kg/day) or VIL (3 mg/kg/day) from 10 to 25 weeks of age. Metabolic and renal functions were assessed; the kidney was removed for histological analysis of glomerulosclerosis and expression of pro-inflammatory/fibrotic markers (RT-PCR and Western blotting); and the aorta was removed for studies of endothelium-dependent relaxation (EDR).

Findings

Hyperinsulinemic ZDF rats typically developed signs of type-2 diabetes and renovascular damage, as evidenced by albuminuria, glomerulosclerosis, and impaired EDR. Neither NWT-03 nor VIL improved metabolic parameters; for VIL, this was despite a 5-fold increase in glucagon-like peptide (GLP)-1 levels. NWT-03 and VIL both reduced renal interleukin (Il)-1β/Il-13 mRNA expression and glomerulosclerosis. However, only NWT-03 additionally decreased renal tumor necrosis factor (TNF)-α mRNA and P22^phox protein expression, reduced albuminuria, and restored aortic EDR. Indomethacin added to the organ bath instantly improved aortic EDR, indicating a role for cyclooxygenase (COX)-derived contractile prostanoids in opposing relaxation in ZDF rats. This indomethacin effect was reduced by NWT-03, but not by VIL, and coincided with decreased renal COX-1/2 protein expression.

Conclusion and Interpretation

Long-term supplementation with the egg protein hydrolysate NWT-03 attenuated renovascular damage in this preclinical rat model of type 2 diabetes. A comparison to the DPP4-inhibitor VIL suggests that the effects of NWT-03 were related to both ACE- and DPP4-inhibitory properties. The development of protein hydrolysates with a multiple-targeting strategy may be of benefit to functional food formulations.

The metabolic syndrome, oxidative stress, environment, and cardiovascular disease: the great exploration

The metabolic syndrome affects 30% of the US population with increasing prevalence. In this paper, we explore the relationship between the metabolic syndrome and the incidence and severity of cardiovascular disease in general and coronary artery disease (CAD) in particular. Furthermore, we look at the impact of metabolic syndrome on outcomes of coronary revascularization therapies including CABG, PTCA, and coronary collateral development. We also examine the association between the metabolic syndrome and its individual component pathologies and oxidative stress. Related, we explore the interaction between the main external sources of oxidative stress, cigarette smoke and air pollution, and metabolic syndrome and the effect of this interaction on CAD. We discuss the apparent lack of positive effect of antioxidants on cardiovascular outcomes in large clinical trials with emphasis on some of the limitations of these trials. Finally, we present evidence for successful use of antioxidant properties of pharmacological agents, including metformin, statins, angiotensin II type I receptor blockers (ARBs), and angiotensin II converting enzyme (ACE) inhibitors, for prevention and treatment of the cardiovascular complications of the metabolic syndrome.

Distinct cardiac and renal effects of ETA receptor antagonist and ACE inhibitor in experimental type 2 diabetes

Diabetic nephropathy is associated with cardiovascular morbidity. Angiotensin-converting enzyme (ACE) inhibitors provide imperfect renoprotection in advanced type 2 diabetes, and cardiovascular risk remains elevated. Endothelin (ET)-1 has a role in renal and cardiac dysfunction in diabetes. Here, we assessed whether combination therapy with an ACE inhibitor and ETA receptor antagonist provided reno- and cardioprotection in rats with overt type 2 diabetes. Four groups of Zucker diabetic fatty (ZDF) rats were treated orally from 4 (when proteinuric) to 8 mo with vehicle, ramipril (1 mg/kg), sitaxsentan (60 mg/kg), and ramipril plus sitaxsentan. Lean rats served as controls. Combined therapy ameliorated proteinuria and glomerulosclerosis mostly as a result of the action of ramipril. Simultaneous blockade of ANG II and ET-1 pathways normalized renal monocyte chemoattractant protein-1 and interstitial inflammation. Cardiomyocyte loss, volume enlargement, and capillary rarefaction were prominent abnormalities of ZDF myocardium. Myocyte volume was reduced by ramipril and sitaxsentan, which also ameliorated heart capillary density. Drug combination restored myocardial structure and reestablished an adequate capillary network in the presence of increased cardiac expression of VEGF/VEGFR-1, and significant reduction of oxidative stress. In conclusion, in type 2 diabetes concomitant blockade of ANG II synthesis and ET-1 biological activity through an ETA receptor antagonist led to substantial albeit not complete renoprotection, almost due to the ACE inhibitor. The drug combination also showed cardioprotective properties, which however, were mainly dependent on the contribution of the ETA receptor antagonist through the action of VEGF.

Combating Combination of Hypertension and Diabetes in Different Rat Models

Rat experimental models are used extensively for studying physiological mechanisms and treatments of hypertension and diabetes co-existence. Each one of these conditions is a major risk factor for cardiovascular disease (CVD), and the combination of the two conditions is a potent enhancer of CVD. Five major animal models that advanced our understanding of the mechanisms and therapeutic approaches in humans are discussed in this review: Zucker, Goto-Kakizaki, SHROB, SHR/NDmcr-cp and Cohen Rosenthal diabetic hypertensive (CRDH) rats. The use of various drugs, such as angiotensin-converting enzyme (ACE) inhibitors (ACEIs), various angiotensin receptor blockers (ARBs), and calcium channel blockers (CCBs), to combat the effects of concomitant pathologies on the combination of diabetes and hypertension, as well as the non-pharmacological approach are reviewed in detail for each rat model. Results from experiments on these models indicate that classical factors contributing to the pathology of hypertension and diabetes combination—Including hypertension, hyperglycemia, hyperinsulinemia and hyperlipidemia—can now be treated, although these treatments do not completely prevent renal complications. Animal studies have focused on several mechanisms involved in hypertension/diabetes that remain to be translated into clinical medicine, including hypoxia, oxidative stress, and advanced glycation. Several target molecules have been identified that need to be incorporated into a treatment modality. The challenge continues to be the identification and interpretation of the clinical evidence from the animal models and their application to human treatment.

Administration of sesamol improved blood-brain barrier function in streptozotocin-induced diabetic rats

Uncontrolled or poorly controlled blood glucose during diabetes is an important factor in worsened vascular function. While evidence suggests that hyperglycemia-induced oxidative stress plays a prominent role in development of microangiopathy of the retina, kidney, and nerves, the role oxidative stress plays on blood-brain barrier (BBB) function and structure has lagged behind. In this study, a natural antioxidant, sesamol, was administered to streptozotocin (STZ)-induced diabetic rats to examine the role that oxidative stress plays on BBB structure and function. Experiments were conducted at 56 days after STZ injection. Male Sprague-Dawley rats randomly were divided into four treatment groups CON--control; STZ--STZ-induced diabetes; CON + S--control + sesamol; STZ + S--STZ-induced diabetes + sesamol. Functional and structural changes to the BBB were measured by in situ brain perfusion and western blot analysis of changes in tight junction protein expression. Oxidative stress markers were visualized by fluorescent confocal microscopy and assayed by spectrophotometric analysis. Results demonstrated that the increased BBB permeability observed in STZ-induced diabetic rats was attenuated in STZ + S rats to levels observed in CON. Sesamol treatment reduced the negative impact of STZ-induced diabetes on tight junction protein expression in isolated cerebral microvessels. Oxidative stress markers were elevated in STZ as compared to CON. STZ + S displayed an improved antioxidant capacity which led to a reduced expression of superoxide and peroxynitrite and reduced lipid peroxidation. In conclusion, this study showed that sesamol treatment enhanced antioxidant capacity of the diabetic brain and led to decreased perturbation of hyperglycemia-induced changes in BBB structure and function.