Effect of intra-arterial insulin on tissue cholesterol and fatty acids in alloxan-diabetic dogs

Rodent Models of Diabetic Retinopathy as a Useful Research Tool to Study Neurovascular Cross-Talk

Diabetes is a group of metabolic diseases leading to dysfunction of various organs, including ocular complications such as diabetic retinopathy (DR). Nowadays, DR treatments involve invasive options and are applied at the sight-threatening stages of DR. It is important to investigate noninvasive or pharmacological methods enabling the disease to be controlled at the early stage or to prevent ocular complications. Animal models are useful in DR laboratory practice, and this review is dedicated to them. The first part describes the characteristics of the most commonly used genetic rodent models in DR research. The second part focuses on the main chemically induced models. The authors pay particular attention to the streptozotocin model. Moreover, this section is enriched with practical aspects and contains the current protocols used in research in the last three years. Both parts include suggestions on which aspect of DR can be tested using a given model and the disadvantages of each model. Although animal models show huge variability, they are still an important and irreplaceable research tool. Note that the choice of a research model should be thoroughly considered and dependent on the aspect of the disease to be analyzed.

An evaluation of pharmacological healing potentialities of Terminalia Arjuna against several ailments on experimental rat models with an in-silico approach

Herbal remedies have been used in many cultures for decades to treat illnesses. These medicinal plants have been found to contain various phytochemical compounds that can help to cure mild to severe illnesses. The inadequacies of conventional medicines and their unusual side effects sparked a determined search for alternative natural therapeutic agents. Another reason for this hunt could be the availability and fewer side effects of natural products. T. arjuna is widely used in traditional medicine to alleviate various diseases like relieving pain, ameliorating diabetes, mitigating inflammation, and back-pedaling of depression. In this study, the ethanolic extract of T. arjuna possesses a promising effect on the animal model (p < 0.05/p < 0.01) as an antihyperglycemic, analgesic, anti-inflammatory, and antidepressant agent, but in a dose-dependent manner. The lower dose of T. arjuna was found to be capable of reversing the disturbed physiological state at a significant level (p < 0.05). However, a higher dose of T. arjuna exerts better therapeutic effects for those diseases. This animal study aims to evaluate the anti-diabetic, anti-depressant, and anti-inflammatory properties of T. arjuna compared to conventional marketed drugs. We will perform an in-silico study for active constituents of T. arjuna against their proposed targets and look for the molecular cascade on their claimed pharmacological properties. This study shows that different doses of T. arjuna bark extracts give similar therapeutic responses compared with established marketed drugs in managing hyperglycemia, stress-induced depression, and inflammation. Besides, our docking study reveals that flavonoids and triterpenoid active constituents of T. arjuna play an important role in its usefulness. This study, therefore, scientifically confirmed the traditional use of this medicinal plant in the management of several diseased conditions.

Insulin Resistance and Atherosclerosis: Implications for Insulin-Sensitizing Agents

Patients with type 2 diabetes mellitus (T2DM) are at high risk for macrovascular complications, which represent the major cause of mortality. Despite effective treatment of established cardiovascular (CV) risk factors (dyslipidemia, hypertension, procoagulant state), there remains a significant amount of unexplained CV risk. Insulin resistance is associated with a cluster of cardiometabolic risk factors known collectively as the insulin resistance (metabolic) syndrome (IRS). Considerable evidence, reviewed herein, suggests that insulin resistance and the IRS contribute to this unexplained CV risk in patients with T2DM. Accordingly, CV outcome trials with pioglitazone have demonstrated that this insulin-sensitizing thiazolidinedione reduces CV events in high-risk patients with T2DM. In this review the roles of insulin resistance and the IRS in the development of atherosclerotic CV disease and the impact of the insulin-sensitizing agents and of other antihyperglycemic medications on CV outcomes are discussed.

Comparison of primary versus secondary prevention of cardiovascular disease in patients with type2 diabetes: Focus on achievement of ABC goals

BACKGROUND

Primary and secondary prevention of cardiovascular disease is of utmost importance in the management of patients with diabetes.

OBJECTIVES

We studied a group of Iranian patients with type2 diabetes to provide an overview of the current status of secondary prevention of cardiovascular disease in the Middle East.

METHODS

This is a cross-sectional study of 2029 Patients with type2 diabetes including 323 patients with coronary artery disease (CAD) were recruited. Achievement of goals in HbA1c (A), blood pressure (B) and LDL-cholesterol(C) was assessed.

RESULTS

The study showed 25.3% of CAD positive patients achieved HbA1c <7% compared to 30% in CAD negative patients. The achievement of blood pressure ≤140/90 mmHg was 53.2% and 52.8% in CAD positive and CAD negative patients respectively. There was no difference in the achievement of all three ABC goals between the two groups (p = 0.733). After logistic regression analysis, history of hypertension had the highest odds ratio for CAD.

CONCLUSION

Although ABC control has an important impact on the prevention of cardiovascular outcomes, the ideal goal needs further efforts to be achieved.

Lipotoxicity in Obesity: Benefit of Olive Oil

The clinical implication of Lipotoxicity in obesity derives primarily from its potential to progress to insulin resistance, endothelial dysfunction and atherosclerosis. Olive oil rich diet decrease accumulation of triglyceride in the liver, improved postprandial triglyceride levels, improve glucose and GLP-1 response in insulin resistant subjects, and up regulate GLUT-2 expression in the liver. The exact molecular mechanism is unknown but, decreasing NFkB activation, decreasing LDL oxidation and improving insulin resistance by less production of inflammatory cytokines (TNF-a, IL-6) and improvement of kinases JNK-mediated phosphorylation of IRS-1 are the principle mechanisms. The beneficial effect of the Mediterranean diet derived from monounsaturated fatty acids (MUFA), mainly from olive oil. In this review we document lipotoxicity in obesity and the benefit of olive oil.

Impact of glucose-lowering drugs on cardiovascular disease in type 2 diabetes

Type 2 diabetes mellitus (T2DM) is characterized by multiple pathophysiologic abnormalities. With time, multiple glucose-lowering medications are commonly required to reduce and maintain plasma glucose concentrations within the normal range. Type 2 diabetes mellitus individuals also are at a very high risk for microvascular complications and the incidence of heart attack and stroke is increased two- to three-fold compared with non-diabetic individuals. Therefore, when selecting medications to normalize glucose levels in T2DM patients, it is important that the agent not aggravate, and ideally even improve, cardiovascular risk factors (CVRFs) and reduce cardiovascular morbidity and mortality. In this review, we examine the effect of oral (metformin, sulfonylureas, meglitinides, thiazolidinediones, DPP4 inhibitors, SGLT2 inhibitors, and α-glucosidase inhibitors) and injectable (glucagon-like peptide-1 receptor agonists and insulin) glucose-lowering drugs on established CVRFs and long-term studies of cardiovascular outcomes. Firm evidence that in T2DM cardiovascular disease can be reversed or prevented by improving glycaemic control is still incomplete and must await large, long-term clinical trials in patients at low risk using modern treatment strategies, i.e., drug combinations designed to maximize HbA1c reduction while minimizing hypoglycaemia and excessive weight gain.

Insulin regulates monocyte trans-endothelial migration through surface expression of macrophage-1 antigen

During the pathogenesis of atherosclerosis, adhesion of monocytes to vascular endothelium and subsequent migration across the endothelium has been recognized as a key process in the chronic inflammatory response in atherosclerosis. As type 2 diabetes is closely associated with the pathogenesis of atherosclerosis, we investigated whether monocyte adhesion and migration were affected by insulin. We found that insulin activated Akt and induced subsequent migration in THP-1. However, glucose and insulin-like growth factor-1, which is a growth factor that is structurally similar to insulin, were not effective. Insulin-dependent migration of THP-1 was blocked by inhibition of PI3K or Akt and by silencing of Akt1. Insulin-dependent migration of bone marrow-derived monocytic cells (BDMCs) was attenuated by inhibition of PI3K and Akt. In addition, BDMCs from Akt1(-/-) mice showed defects in insulin-dependent migration. Stimulation of THP-1 with insulin caused adhesion with human vein endothelial cells (HUVECs) that was blocked by silencing of Akt1. However, stimulation of HUVECs did not cause adhesion with THP-1. Moreover, BDMCs from Akt1(-/-) mice showed defects in insulin-dependent adhesion with HUVECs. Insulin induced surface expression of Mac-1, and neutralization of Mac-1 blocked insulin-induced adhesion of THP-1 as well as BDMCs. Surface expression of Mac-1 was blocked in THP-1 with silenced Akt1, and in BDMCs isolated from mice lacking Akt1. Finally, trans-endothelial migration of THP-1 and BDMCs was blocked by Mac-1-neutralizing antibody, in THP-1 with silenced Akt1 and in BDMCs from Akt1(-/-) mice. These results suggest that insulin stimulates monocyte trans-endothelial migration through Akt-dependent surface expression of Mac-1, which may be part of the atherogenesis in type 2 diabetes.

Positive correlation between chronic hyperglycemia and serum fetuin-A levels in middle-aged and elderly Chinese

BACKGROUND

The aim of the present study was to evaluate the association between HbA1c and serum fetuin-A levels in middle-aged and elderly Chinese.

METHODS

A total of 3790 subjects (1519 men; 2271 women) aged ≥40 years were enrolled in this cross-sectional study in the Songnan community of Baoshan District, Shanghai, China. HbA1c levels were used to determine the presence of chronic hyperglycemia. Subjects were divided into three groups based on HbA1c levels: <6.5%, 6.5% ≤ HbA1c < 7.0%, and HbA1c ≥ 7.0%. "Elevated" fetuin-A levels were defined as serum levels in the upper quartile (i.e. ≥367.39 mg/L).

RESULTS

Mean serum fetuin-A levels were higher in subjects with HbA1c ≥ 7.0% compared with those in whom HbA1c was <6.5% (309.32 vs 290.83 mg/L, respectively). Multivariate linear regression analysis revealed a significant positive correlation between HbA1c and serum fetuin-A levels (β = 0.07; SE = 0.03; P = 0.04). After adjustment for possible confounders, an increased percentage of subjects with elevated fetuin-A levels was found in the group with HbA1c ≥ 7.0% compared with the group in which HbA1c was <6.5% (odds ratio 1.38; 95% confidence interval 1.09-1.74). Interactions were found between HbA1c and both insulin resistance and the urinary albumin-to-creatinine ratio for the percentage of elevated fetuin-A levels (P(interaction) = 0.002 and 0.05, respectively).

CONCLUSIONS

In Chinese adults, a positive correlation was found between chronic hyperglycemia and serum fetuin-A levels. Further research into the mechanisms underlying fetuin-A regulation is needed to identify potential drug targets.

Reducing cardiovascular disease risk in patients with type 2 diabetes and concomitant macrovascular disease: can insulin be too much of a good thing?

Despite improvement of microvascular outcomes as a consequence of optimal glucose control in patients with type 2 diabetes, prevention of macrovascular complications is still a major challenge. Of interest, large-scale intervention studies (Action to Control Cardiovascular Risk in Diabetes, Action in Diabetes and Vascular Disease-Preterax and Diamicron Modified Release Controlled Evaluation and Veterans Affairs Diabetes Trial) comparing standard therapy versus more intensive glucose-lowering therapy failed to report beneficial impacts on macrovascular outcomes. Consequently, it is currently under debate whether the high doses of exogenous insulin that were administered in these trials to achieve strict target glucose levels could be responsible for these unexpected outcomes. Additionally, a potential role for plasma insulin levels in predicting macrovascular outcomes has emerged in patients with or without type 2 diabetes. These observations, combined with evidence from in vitro and animal experiments, suggest that insulin might have intrinsic atherogenic effects. In this review, we summarize clinical trials, population-based studies as well as data emerging from basic science experiments that point towards the hypothesis that the administration of high insulin doses might not be beneficial in patients with type 2 diabetes and established macrovascular disease.

Assessment and treatment of cardiovascular risk in prediabetes: impaired glucose tolerance and impaired fasting glucose

Individuals with impaired glucose tolerance (IGT) and/or impaired fasting glucose (IFG) are at high risk, not only to develop diabetes mellitus, but also to experience an adverse cardiovascular (CV) event (myocardial infarction, stroke, CV death) later in life. The underlying pathophysiologic disturbances (insulin resistance and impaired β-cell function) responsible for the development of type 2 diabetes are maximally/near maximally expressed in subjects with IGT/IFG. These individuals with so-called prediabetes manifest all of the same CV risk factors (dysglycemia, dyslipidemia, hypertension, obesity, physical inactivity, insulin resistance, procoagulant state, endothelial dysfunction, inflammation) that place patients with type 2 diabetes at high risk for macrovascular complications. The treatment of these CV risk factors should follow the same guidelines established for patients with type 2 diabetes, and should be aggressively followed to reduce future CV events.

Cellular and molecular mechanisms of vascular injury in diabetes--part I: pathways of vascular disease in diabetes

Diabetes-induced micro- and macrovascular complications are the major causes of morbidity and mortality in diabetic patients. While hyperglycemia is a key factor for the pathogenesis of diabetic microvascular complications, it is only one of the multiple factors capable of increasing the risk of macrovascular complications. Hyperglycemia induces vascular damage probably through a single common pathway - increased intracellular oxidative stress - linking four major mechanisms, namely the polyol pathway, advanced glycation end-products (AGEs) formation, the protein kinase C (PKC)-diacylglycerol (DAG) and the hexosamine pathways. In addition, in conditions of insulin resistance, i.e., preceding the onset of type 2 diabetes, the phosphatidylinositol (PI) 3-kinase (PI3K)/Akt pathway is selectively inhibited, while the mitogen activated protein (MAP)-kinase pathway remains largely unaffected, thus allowing compensatory hyperinsulinemia to elicit pro-atherogenic events in vascular smooth muscle and endothelial cells, including increased cell proliferation, and the expression of plasminogen activator inhibitor-1, as well as of proinflammatory cytokines and endothelial adhesion molecules.

Insulin resistance, lipotoxicity, type 2 diabetes and atherosclerosis: the missing links. The Claude Bernard Lecture 2009

Insulin resistance is a hallmark of type 2 diabetes mellitus and is associated with a metabolic and cardiovascular cluster of disorders (dyslipidaemia, hypertension, obesity [especially visceral], glucose intolerance, endothelial dysfunction), each of which is an independent risk factor for cardiovascular disease (CVD). Multiple prospective studies have documented an association between insulin resistance and accelerated CVD in patients with type 2 diabetes, as well as in non-diabetic individuals. The molecular causes of insulin resistance, i.e. impaired insulin signalling through the phosphoinositol-3 kinase pathway with intact signalling through the mitogen-activated protein kinase pathway, are responsible for the impairment in insulin-stimulated glucose metabolism and contribute to the accelerated rate of CVD in type 2 diabetes patients. The current epidemic of diabetes is being driven by the obesity epidemic, which represents a state of tissue fat overload. Accumulation of toxic lipid metabolites (fatty acyl CoA, diacylglycerol, ceramide) in muscle, liver, adipocytes, beta cells and arterial tissues contributes to insulin resistance, beta cell dysfunction and accelerated atherosclerosis, respectively, in type 2 diabetes. Treatment with thiazolidinediones mobilises fat out of tissues, leading to enhanced insulin sensitivity, improved beta cell function and decreased atherogenesis. Insulin resistance and lipotoxicity represent the missing links (beyond the classical cardiovascular risk factors) that help explain the accelerated rate of CVD in type 2 diabetic patients.

Insulin is a stronger inducer of insulin resistance than hyperglycemia in mice with type 1 diabetes mellitus (T1DM)

Subjects with type 1 diabetes mellitus (T1DM) eventually develop insulin resistance and other features of T2DM such as cardiovascular disorders. The exact mechanism has been not been completely understood. In this study, we tested the hypothesis that excessive or inappropriate exposure to insulin is a primary mediator of insulin resistance in T1DM. We found that continuous exposure of mice with non-obese diabetes to insulin detemir, which is similar to some current conventional treatment of human T1DM, induced severe insulin resistance, whereas untreated hyperglycemia for the same amount of time (2 weeks) did not cause obvious insulin resistance. Insulin resistance was accompanied by decreased mitochondrial production as evaluated by mitochondrial DNA and levels of transcripts and proteins of mitochondrion-associated genes, increased ectopic fat accumulation in liver and skeletal muscle (gastrocnemius) evaluated by measurements of triglyceride content, and elevated oxidative stress detected by the GSH/GSSG ratio. Prolonged exposure of cultured hepatocytes to insulin induced significant insulin resistance, whereas the same length of exposure to a high level of glucose (33 mm) did not cause obvious insulin resistance. Furthermore, our results showed that prolonged exposure to insulin caused oxidative stress, and blockade of mitochondrion-derived oxidative stress by overexpression of manganese-superoxide dismutase prevented insulin resistance induced by the prolonged exposure to insulin. Together, our results show that excessive exposure to insulin is a primary inducer of insulin resistance in T1DM in mice.

The insulin resistance syndrome: physiological considerations

The insulin resistance syndrome, also referred to as the metabolic syndrome or syndrome X, is associated with a primary cellular defect in insulin action (insulin resistance) and a compensatory increase in insulin secretion. The combination of insulin resistance and subsequent hyperinsulinaemia causes a number of metabolic and cardiovascular changes that result in a syndrome typically characterised by type 2 diabetes, obesity, dyslipidaemia, coronary artery disease and hypertension. Moreover, disturbances in sleep (sleep apnoea) and ovarian dysfunction are also characterised by insulin resistance. The pathophysiological basis for these disturbances reflects the impact of variable genetic and environmental influences. At a molecular level, insulin resistance involves defects of insulin signalling such as reduced insulin receptor tyrosine kinase activity and reduced post-receptor phosphorylation steps that impinge on metabolic and vascular effects of insulin.

Time from diagnosis of type 2 diabetes to initiation of insulin therapy is related to carotid artery intima-media thickness

To investigate the association between time from diagnosis of type 2 diabetes to initiation of insulin therapy (pre-exogenous insulin period) and intima-media thickness (IMT) of the common carotid artery (CCA), a cross-sectional analysis was conducted among 98 males and 193 females (90% Hispanic) with type 2 diabetes, aged 30-70 years old. The association between the pre-exogenous insulin period and the primary outcome was examined in men and women using analysis of covariance (ANCOVA) with adjustment for current age, duration of insulin therapy, low-density lipoprotein (LDL) cholesterol, systolic blood pressure and hemoglobin A1c. The pre-exogenous insulin period was significantly and linearly associated with mean IMT of the CCA in men. In women, the linear trend was not significant while a significant quadratic trend was noted across three categories of the pre-exogenous insulin period (0-5, 6-10, 11-24 years). Longitudinal data are needed to determine the effect of early initiation of insulin therapy on the progression of subclinical atherosclerosis among persons with diabetes.

Hyperinsulinemia during oral glucose tolerance test is associated with increased neointimal tissue proliferation after coronary stent implantation in nondiabetic patients: a serial intravascular ultrasound study

OBJECTIVES

The purpose of this study was to determine whether hyperinsulinemia during the oral glucose tolerance test is associated with increased neointimal tissue proliferation after coronary stent implantation in nondiabetic patients.

BACKGROUND

Although hyperinsulinemia induces increased vascular smooth muscle cell proliferation in experimental models, it has not been determined whether hyperinsulinemia is associated with increased neointimal tissue proliferation after coronary stent implantation.

METHODS

Serial (postintervention and six-month follow-up) intravascular ultrasound (IVUS) was used to study 67 lesions treated with Palmaz-Schatz stents in 55 nondiabetic patients. Cross-sectional images within stents were taken at every 1 mm, using an automatic pullback, and a neointimal index was calculated as the ratio between the averaged neointimal area and averaged stent area. All patients underwent a 75-g oral glucose tolerance test. Plasma glucose (PG) and immunoreactive insulin (IRI) levels were measured at baseline and 1 and 2 h after the glucose load. The sum of PGs (sigmaPG) and the sum of IRIs (sigmaIRI) were calculated. Body mass index (BMI), lipid levels, and glycosylated hemoglobin levels were measured.

RESULTS

There were 27 patients with normal glucose tolerance, and 28 patients with impaired glucose tolerance (IGT). The neointimal index in patients with IGT was greater than that in patients with normal glucose tolerance (42.9 +/- 14% vs. 24.9 +/- 8.3%, respectively, p < 0.0001). Linear regression analysis showed that the neointimal index at follow-up correlated well with sigmaPG (p < 0.0001), fasting IRI (p < 0.0001), sigmaIRI (p < 0.0001), triglyceride level (p = 0.018), and BMI (p < 0.0001). Multiple regression analysis revealed that sigmaIRI (p = 0.0002) and sigmaPG (p = 0.0034) were the best predictors of the greater neointimal index at follow-up.

CONCLUSIONS

Serial IVUS assessment shows that hyperinsulinemia during an oral glucose tolerance test is associated with increased neointimal tissue proliferation after coronary stent implantation in nondiabetic patients.

Microalbuminuria in essential hypertension: significance, pathophysiology, and therapeutic implications

Some patients with essential hypertension manifest greater than normal urinary albumin excretion (UAE). The significance of this association, which is the object of this review, is not well established. Hypertensive patients with microalbuminuria manifest greater levels of blood pressure, particularly at night, and higher serum levels of cholesterol, triglycerides, and uric acid than patients with normal UAE. Levels of high-density lipoprotein cholesterol, on the other hand, were lower in patients with microalbuminuria than in those with normal UAE. Patients with microalbuminuria manifested greater incidence of insulin resistance and thicker carotid arteries than patients with normal UAE. After a follow-up of 7 years, we observed that 12 cardiovascular events occurred among 54 (21.3%) patients with microalbuminuria and only two such events among 87 patients with normal UAE (P < 0.0002). Stepwise logistic regression analysis showed that UAE, cholesterol level, and diastolic blood pressure were independent predictors of the cardiovascular outcome. Rate of creatinine clearance from patients with microalbuminuria decreased more than that from those with normal UAE. In conclusion, these studies suggest that hypertensive individuals with microalbuminuria manifest a variety of biochemical and hormonal derangements with pathogenic potential, which results in hypertensive patients having a greater incidence of cardiovascular events and a greater decline in renal function than patients with normal UAE.

Hyperinsulinemia and insulin resistance in hypertension: differential effects of antihypertensive agents

Both hypertension and diabetes mellitus are multifaceted dynamic expressions of pathophysiological disequilibrium that are closely related with and even intermingled by a number of common factors. Hyperinsulinaemia and insulin resistance may be possible links between hypertension and diabetes mellitus. While working on the effect of different antihypertensive agents in several animal models of simultaneously occurring diabetes-mellitus and hypertension it was found that most antihypertensives prevented streptozotocin (STZ)-induced hypertension in rats. Hydralazine, angiotensin converting enzyme (ACE) inhibitors, calcium channel blockers (CCB) and clonidine prevented STZ-induced cardiomyopathy, hyperlipidaemia and glucose tolerance. It was further demonstrated that atenolol produced many unfavourable effects like hyperlipidaemia and decreased cardiac functions. We also used other animal models of simultaneously occurring diabetes-mellitus and hypertension such as genetically hypertensive or spontaneously hypertensive (SH), Deoxycorticosterone acetate (DOCA)-hypertensive and neonatal streptozotocin-induced NIDDM rats. Results of our studies suggest that SH, neonatal STZ-induced NIDDM, and fructose hypertensive rat models may be considered as models for insulin resistance - the concept that has come into limelight in recent years. DOCA may have some influence on glucose homeostasis and insulin sensitivity and some sort of counteraction to STZ-induced cardiovascular and metabolic changes occur with DOCA. Hence, it may not be considered as an ideal model to study the metabolic and cardiovascular complications of hypertension associated with diabetes-mellitus. Among ACE inhibitors, perindopril, spirapril, and among calcium channel blockers (CCB) used in our study amlodipine and nifedipine were found to produce an increase in insulin sensitivity. Enalapril, ramipril, lisinopril and nitrendipine failed to alter insulin sensitivity as far as the glycaemic control is concerned. Extension of the results of these experiments to the clinical practice substantiated many of the findings and a good correlation between results obtained from experimental studies and clinical data was found.