The role of the angiotensin system in cardiac glucose homeostasis: therapeutic implications

ACE inhibitors and their interaction with systems and molecules involved in metabolism

The main function of the renin-angiotensin-aldosterone system (RAAS) is the regulation of blood pressure; therefore, researchers have focused on its study to treat cardiovascular and renal diseases. One of the most widely used treatments derived from the study of RAAS, is the use of angiotensin-converting enzyme inhibitors (ACEi). Since it was discovered, the main target of ACEi has been the cardiovascular and renal systems. However, being the RAAS expressed locally in several specialized tissues and cells such as pneumocytes, hepatocytes, spleenocytes, enterocytes, adipocytes, and neurons the effect of inhibitors has expanded, because it is expected that RAAS has a role in the specific function of those cells. Many chronic degenerative diseases compromise the correct function of those organs, and in most of them, the RAAS is overactivated. Therefore, the use of ACEi must exert a benefit on an impaired system. Accordingly, the objective of this review is to present a brief overview of the cardiovascular and renal actions of ACEi and its effects in organs that are not the classic targets of ACEi that carry on glucose and lipid metabolism.

Haplotype analysis of PPARγ C681G and intron CT variants. Positive association with essential hypertension

BACKGROUND

There is strong evidence suggesting an association between the peroxisome-activated receptor γ (PPARγ) gene and multimetabolic disorders. The association of PPARγ genetic variants with essential hypertension (EH) has not yet been investigated. The aim of this study was to investigate the association between the PPARγ gene (C681G and intron CT) and EH, examining the polymorphism and haplotype in a Han Chinese population.

METHODS

Participants were recruited within the framework of the PMMJS cohort population survey in an urban community of Jiangsu Province, China. Two single-nucleotide polymorphisms (SNPs) previously reported to be associated with multimetabolic disorders and the reasonable coverage of the PPARγ gene region were analyzed with TaqMan SNP genotyping assays.

RESULTS

C681G and intron CT were significantly associated with an increased risk of EH both in the codominant model and the dominant model after adjusting for potential nongenetic risk factors. Analysis of the haplotype association revealed that the risk of EH was significantly increased among individuals carrying the GC (odds ratio, 95 % CI: 1.60, 1.21-2.11), CT (1.45, 1.03-2.11), and GT haplotypes (1.95, 1.17-3.23) compared with those carrying the CC haplotype.

CONCLUSION

The polymorphisms of C681G and intron CT were significantly associated with the risk of EH, and the GC, CT, and GT haplotypes established by C681G and intron CT are likely to be genetic markers of EH in the Han Chinese population.

Renin-angiotensin-aldosterone blockade for cardiovascular disease prevention

The renin-angiotensin-aldosterone system (RAAS) plays a significant role in pathophysiology of multiple disease states. RAAS blockade is beneficial in patients with hypertension, acute myocardial infarction, chronic heart failure, stroke, and diabetic renal disease. RAAS blockade with the combination angiotensin-converting enzyme inhibitors (ACEIs) and angiotensin receptor blockers (ARBs) has demonstrated conflicting results in recent clinical trials. This article reviews the latest evidence of isolated ACEI or ARB use, their combination, and the role of aldosterone blockers and direct renin inhibitors in patients at risk, and makes recommendations for their use in the prevention of morbidity and mortality in cardiovascular disease.

IGF-1 and atherothrombosis: relevance to pathophysiology and therapy

IGF-1 (insulin-like growth factor-1) plays a unique role in the cell protection of multiple systems, where its fine-tuned signal transduction helps to preserve tissues from hypoxia, ischaemia and oxidative stress, thus mediating functional homoeostatic adjustments. In contrast, its deprivation results in apoptosis and dysfunction. Many prospective epidemiological surveys have associated low IGF-1 levels with late mortality, MI (myocardial infarction), HF (heart failure) and diabetes. Interventional studies suggest that IGF-1 has anti-atherogenic actions, owing to its multifaceted impact on cardiovascular risk factors and diseases. The metabolic ability of IGF-1 in coupling vasodilation with improved function plays a key role in these actions. The endothelial-protective, anti-platelet and anti-thrombotic activities of IGF-1 exert critical effects in preventing both vascular damage and mechanisms that lead to unstable coronary plaques and syndromes. The pro-survival and anti-inflammatory short-term properties of IGF-1 appear to reduce infarct size and improve LV (left ventricular) remodelling after MI. An immune-modulatory ability, which is able to suppress 'friendly fire' and autoreactivity, is a proposed important additional mechanism explaining the anti-thrombotic and anti-remodelling activities of IGF-1. The concern of cancer risk raised by long-term therapy with IGF-1, however, deserves further study. In the present review, we discuss the large body of published evidence and review data on rhIGF-1 (recombinant human IGF-1) administration in cardiovascular disease and diabetes, with a focus on dosage and safety issues. Perhaps the time has come for the regenerative properties of IGF-1 to be assessed as a new pharmacological tool in cardiovascular medicine.

Next generation multifunctional angiotensin receptor blockers

Angiotensin receptor blockers (ARBs) are well-tolerated drugs that are known to be useful for inhibiting activity of the renin-angiotensin (RAS) system, treating hypertension and reducing the risk for cardiovascular disease. However, inhibition of the RAS does not control all pathophysiological mechanisms of hypertension or cardiovascular risk and many patients continue to suffer from cardiovascular events and metabolic disturbances despite being treated with an ARB, an angiotensin-converting enzyme inhibitor or both, in addition to other standard therapies for cardiovascular disease. Recently, it has become apparent that bifunctional molecules can be designed that do more than just block AT(1) receptors and that can target additional mechanisms of hypertension, cardiovascular disease and diabetes besides just increased activity of the renin-angiotensin system. Specifically, next generation ARBs are becoming available that are intended to not only antagonize AT(1) receptors, but also block endothelin receptors, function as nitric oxide donors, inhibit neprilysin activity and increase natriuretic peptide levels, or stimulate the peroxisome proliferator-activated receptor gamma (PPARgamma). In this review, we: (1) discuss the potential importance of multifunctional ARBs that can reduce cardiovascular and metabolic risk through multiple mechanisms that go beyond just inhibition of the renin-angiotensin system and (2) describe specific examples of next generation ARBs in development that are intended to do more than simply block AT(1) receptors.

Doxazosin in metabolically complicated hypertension

Metabolic syndrome, a cluster of metabolic abnormalities with visceral obesity and insulin resistance as its central component, is highly prevalent among hypertensive patients. Hypertension complicated by metabolic syndrome is associated with an increased risk of cardiovascular disease and new-onset Type II diabetes mellitus that further aggravates the prognostic outlook. Such a complex condition requires a multifactorial intervention including blood pressure lowering, improvement of the adverse metabolic profile and delayed onset of new diabetes. In this respect, doxazosin and other alpha-1 adrenoceptor blocking agents are of interest given their effect on the lipid profile in dyslipidemic, obese hypertensive patients, either diabetic or not. Doxazosin improves insulin sensitivity, apparently by accelerating insulin and glucose disposal through vasodilatation of skeletal muscle vascular beds. Whether long-term treatment with the drug might delay, or possibly prevent, incident Type II diabetes in hypertension complicated by metabolic syndrome is an intriguing possibility to be tested in appropriately designed clinical trials.

Effects of insulin replacements, inhibitors of angiotensin, and PKCbeta's actions to normalize cardiac gene expression and fuel metabolism in diabetic rats

High-density oligonucleotide arrays were used to compare gene expression of rat hearts from control, untreated diabetic, and diabetic groups treated with islet cell transplantation (ICT), protein kinase C (PKC)beta inhibitor ruboxistaurin, or ACE inhibitor captopril. Among the 376 genes that were differentially expressed between untreated diabetic and control hearts included key metabolic enzymes that account for the decreased glucose and increased free fatty acid utilization in the diabetic heart. ICT or insulin replacements reversed these gene changes with normalization of hyperglycemia, dyslipidemia, and cardiac PKC activation in diabetic rats. Surprisingly, both ruboxistaurin and ACE inhibitors improved the metabolic gene profile (confirmed by real-time RT-PCR and protein analysis) and ameliorated PKC activity in diabetic hearts without altering circulating metabolites. Functional assessments using Langendorff preparations and (13)C nuclear magnetic resonance spectroscopy showed a 36% decrease in glucose utilization and an impairment in diastolic function in diabetic rat hearts, which were normalized by all three treatments. In cardiomyocytes, PKC inhibition attenuated fatty acid-induced increases in the metabolic genes PDK4 and UCP3 and also prevented fatty acid-mediated inhibition of basal and insulin-stimulated glucose oxidation. Thus, PKCbeta or ACE inhibitors may ameliorate cardiac metabolism and function in diabetes partly by normalization of fuel metabolic gene expression directly in the myocardium.

Metabolic actions of angiotensin receptor antagonists: PPAR-gamma agonist actions or a class effect?

Accumulating basic and clinical data support the hypothesis that angiotensin receptor blockers have beneficial effects on glucose and lipid metabolism that are not shared by other classes of antihypertensive agents. These metabolic actions might only partially be shared by angiotensin-converting enzyme inhibitors. Specific benefits beyond those of other angiotensin receptor blockers have been claimed for telemesartan and, to a lesser extent, irbesartan based on a partial agonist action on PPAR-gamma receptors. Although the evidence is strong in vitro, specific actions not shared by other angiotensin receptor blockers have not yet been convincingly demonstrated in vivo or in clinical trials. In many cases, a full range of doses has not been compared, and the apparent superiority of telmesartan could be an artifact of its higher receptor binding affinity, greater tissue penetration owing to lipophilicity, and longer half life.

The role of renin–angiotensin system inhibition in the treatment of hypertension in metabolic syndrome: are all the angiotensin receptor blockers equal?

The metabolic syndrome (MetS) is a strong predictor of cardiovascular morbidity and mortality, as well as new Type 2 diabetes. MetS consists of visceral obesity, elevated blood pressure, impaired glucose metabolism, atherogenic dyslipidaemia (elevated triglycerides and low levels of high-density lipoprotein cholesterol), as well as other metabolic abnormalities. The underlying pathophysiology seems to be largely, but not uniquely, attributable to insulin resistance. Existing antihypertensive drugs were designed to lower blood pressure rather than to modify the metabolic abnormalities associated with hypertension. This review considers the role of renin-angiotensin system inhibition and especially the use of angiotensin receptor blockers (ARBs) in the treatment of hypertension in MetS. There are differences among ARBs. Among them is the uricosuric effect of losartan. Furthermore, telmisartan may function as a partial agonist of the peroxisome proliferator-activated receptor-gamma (PPAR-gamma).

Metabolic effects of antihypertensive agents: role of sympathoadrenal and renin-angiotensin systems

Reports of beneficial, neutral and adverse impacts of antihypertensive drug classes on glucose and lipid metabolism can be found in human data. Furthermore, mechanisms for these diverse effects are often speculative and controversial. Clinical trial data on the metabolic effects of antihypertensive agents are highly contradictory. Comparisons of clinical trials involving different agents are complicated by differences in the spectrum of metabolic disturbances that accompany hypertension in different groups of patients. Two physiological systems are predominant at the interface between metabolic and cardiovascular regulation: the sympathetic nervous system (SNS) and the renin-angiotensin system (RAS). These two systems are major targets of antihypertensive drug actions, and also mediate many of the beneficial and adverse effects of antihypertensive agents on glucose and lipid metabolism. Thiazides and beta-adrenergic antagonists can adversely affect glucose and lipid metabolism, which are frequently compromised in human essential hypertension, and increase the incidence of new cases of diabetes. Laboratory studies confirm these effects, and suggest that compensatory activation of the SNS and RAS may be one mechanism. Other antihypertensives directly targeting the SNS and RAS may have beneficial effects on glucose and lipid metabolism, and may prevent diabetes. Resolution of the controversies surrounding the metabolic effects of antihypertensive agents can only be resolved by further laboratory studies, in addition to controlled clinical trials.

The renin angiotensin system as a therapeutic target to prevent diabetes and its complications

The role of the RAAS in development and maintenance of blood pressure is well established. In addition, the deleterious effects of angiotensin II on the heart, vasculature, and kidneys have been clearly defined. There seems to be a close relationship between endothelial dysfunction, insulin resistance (a precursor to diabetes and coronary artery disease) and angiotensin II. The signaling pathways for insulin in the vascular wall interacts with the angiotensin signaling, giving rise to potential mechanisms for development of diabetes and resulting harmful effects. A large number of clinical trials using ACE inhibitors or ARBs have shown significant reduction in secondary endpoints in the development of new onset of diabetes. Ongoing prospective studies involving ARBs (eg, the Nateglinide and Valsartan Impaired Glucose Tolerance Outcomes Research trial) and ACE inhibitors (eg, the Diabetes Re-duction Assessment with Ramipril and Rosiglita-zone Medication trial) are testing the ability of certain agents to prevent type 2 diabetes. In the meantime, it is important to recognize insulin resistance and metabolic syndrome as entities that increase the risk for cardiovascular disease. In addition to lifestyle modifications, managing endothelial dysfunction and protecting the vasculature will help prevent diabetes and cardiovascular disease.

Prevention of type 2 diabetes mellitus through inhibition of the Renin-Angiotensin system

Type 2 diabetes mellitus is becoming a major health problem associated with excess morbidity and mortality. As the prevalence of type 2 diabetes is rapidly increasing, prevention of the disease should be considered as a key objective in the near future. Besides lifestyle changes, various pharmacological treatments have proven their efficacy in placebo-controlled clinical trials, including antidiabetic drugs such as metformin, acarbose and troglitazone, or antiobesity agents such as orlistat. Arterial hypertension, a clinical entity in which insulin resistance is common, is strongly associated with type 2 diabetes and may precede the disease by several years. While antihypertensive agents such as diuretics or beta-adrenoceptor antagonists may worsen insulin resistance and impair glucose tolerance, newer antihypertensive agents exert neutral or even slightly positive metabolic effects. Numerous clinical trials have investigated the effects of ACE inhibitors or angiotensin II receptor antagonists (ARAs) on insulin sensitivity in hypertensive patients, with or without diabetes, with no consistent results. Almost half of the studies with ACE inhibitors in hypertensive nondiabetic individuals demonstrated a slight but significant increase in insulin sensitivity as assessed by insulin-stimulated glucose disposal during a euglycaemic hyperinsulinaemic clamp, while the other half failed to reveal any significant change. The effects of ARAs on insulin sensitivity are neutral in most studies. Mechanisms of improvement of glucose tolerance and insulin sensitivity through the inhibition of the renin-angiotensin system (RAS) are complex. They may include improvement of blood flow and microcirculation in skeletal muscles and, thereby, enhancement of insulin and glucose delivery to the insulin-sensitive tissues, facilitating insulin signalling at the cellular level and improvement of insulin secretion by the beta cells. Six recent large-scale clinical studies reported a remarkably consistent reduction in the incidence of type 2 diabetes in hypertensive patients treated with either ACE inhibitors or ARAs for 3-6 years, compared with a thiazide diuretic, beta-adrenoceptor antagonist, the calcium channel antagonist amlodipine or even placebo. The relative risk reduction averaged 14% (p = 0.034) in the CAPPP (Captopril Prevention Project) with captopril compared with a thiazide or beta1-adrenoceptor antagonist, 34% (p < 0.001) in the HOPE (Heart Outcomes Prevention Evaluation) study with ramipril compared with placebo, 30% (p < 0.001) in the ALLHAT (Antihypertensive and Lipid-Lowering Treatment to Prevent Heart Attack Trial) with lisinopril compared with chlortalidone, 25% (p < 0.001) in the LIFE (Losartan Intervention For Endpoint reduction in hypertension study) with losartan compared with atenolol, and 25% (p = 0.09) in the SCOPE (Study on Cognition and Prognosis in the Elderly) with candesartan cilexetil compared with placebo, and 23% (p < 0.0001) in the VALUE (Valsartan Antihypertensive Long-term Use Evaluation) trial with valsartan compared with amlodipine. All these studies considered the development of diabetes as a secondary endpoint, except the HOPE trial where it was a post hoc analysis. These encouraging observations led to the initiation of two large, prospective, placebo-controlled randomised clinical trials whose primary outcome is the prevention of type 2 diabetes: the DREAM (Diabetes REduction Approaches with ramipril and rosiglitazone Medications) trial with the ACE inhibitor ramipril and the NAVIGATOR (Nateglinide And Valsartan in Impaired Glucose Tolerance Outcomes Research) trial with the ARA valsartan. Finally, ONTARGET (ONgoing Telmisartan Alone and in combination with Ramipril Global Endpoint Trial) will also investigate as a secondary endpoint whether it is possible to prevent the development of type 2 diabetes by blocking the RAS with either an ACE inhibitor or an ARA or a combination of both. Thus, the recent consistent observations of a 14-34% reduction of the development of diabetes in hypertensive patients receiving ACE inhibitors or ARAs are exciting. From a theoretical point of view, they emphasise that there are many aspects of the pathogenesis, prevention and treatment of type 2 diabetes that still need to be uncovered. From a practical point of view, they may offer a new strategy to reduce the ongoing epidemic and burden of type 2 diabetes.

Antidiabetic mechanisms of angiotensin-converting enzyme inhibitors and angiotensin II receptor antagonists: beyond the renin-angiotensin system

Several lines of evidence suggest that angiotensin-converting enzyme (ACE) inhibitors and some angiotensin II receptor blockers (ARBs) may improve insulin sensitivity and decrease the risk for type 2 diabetes. It is widely assumed that the potential antidiabetic properties of these agents are largely mediated by their ability to interfere with the adverse metabolic effects of angiotensin II. However, recent studies suggest that ACE inhibitors might improve glucose metabolism primarily through effects on kinin-nitric oxide pathways. In addition, one ARB in particular, telmisartan, has been found to effectively activate the peroxisome proliferator activated receptor gamma (PPARgamma), a well-known target for insulin-sensitizing, antidiabetic drugs. Thus, the beneficial metabolic effects of some ACE inhibitors and ARBs may go well beyond their effects on the renin-angiotensin system. Moreover, the identification of telmisartan as a unique angiotensin II receptor antagonist with selective PPARgamma modulating ability suggests new opportunities for developing third-generation ARBs and PPARgamma activators, with enhanced potential for treating hypertension, diabetes and the metabolic syndrome.

Effects of telmisartan compared with eprosartan on blood pressure control, glucose metabolism and lipid profile in hypertensive, type 2 diabetic patients: a randomized, double-blind, placebo-controlled 12-month study

We evaluated the antihypertensive activity, glucose homeostasis and plasma lipid profile in patients with mild hypertension and type 2 diabetes mellitus treated by diet and exercise, and not in receipt of oral hyperglycemics, following 12-month treatment with either telmisartan or eprosartan. In this double-blind, placebo-controlled trial, 119 patients with mild essential hypertension (diastolic blood pressure [DBP] 91-104 mmHg) and type 2 diabetes were divided into three groups and randomized to receive once-daily telmisartan 40 mg, eprosartan 600 mg, or placebo for 12 months. At enrollment, patients were advised on diet (1,400-1,600 kcal/day) and exercise (physical aerobics on a bicycle for at least 30 min on 4 days each week). Compared with baseline, a significant reduction (p<0.01) in seated trough systolic blood pressure (SBP) was detected after 12-month treatment with either telmisartan or eprosartan. Seated trough DBP was also reduced by telmisartan (p<0.01) and eprosartan (p<0.05); the antihypertensive effect of telmisartan was significantly superior (p<0.05). No change in body mass index or glucose metabolism was observed with either active treatment, or with placebo. Telmisartan, but not eprosartan, significantly improved plasma total cholesterol (p<0.01), low-density lipoprotein cholesterol (p<0.01) and triglycerides (p<0.05) compared with eprosartan. In conclusion, 12-month telmisartan treatment produced a significantly greater reduction in DBP than eprosartan and significantly improved plasma lipids. The improvement could be due to varying pharmacokinetic/pharmacodynamic properties of telmisartan compared with eprosartan, even if it is not clear about the relationship between angiotensin-II receptor blockade and 3-hydroxy-3-methylglutaryl-coenzyme A reductase inhibition.

Renin-angiotensin system inhibition prevents type 2 diabetes mellitus

The inhibition of the renin-angiotensin system (RAS) with either angiotensin converting enzyme inhibitors (ACEIs) or AT1 angiotensin receptor blockers (ARBs) consistently and significantly reduces the incidence of type 2 diabetes in patients with hypertension or congestive heart failure. The mechanisms underlying this protective effect appear to be complex and may involve an improvement of both insulin sensitivity and insulin secretion. These two effects may result, at least in part, from the well known effects of these pharmacological agents on the vascular system on the one hand, on the ionic balance on the other hand. Indeed, the vasodilation induced by ACEIs or ARBs could improve the blood circulation in skeletal muscles, thus favouring peripheral insulin action, but also in the pancreas, thus promoting insulin secretion. Preserving cellular potassium and magnesium pools by blocking the aldosterone effects could also improve both cellular insulin action and insulin secretion. However, besides these classical effects, new mechanisms have been recently suggested. A direct effect of the inhibition of angiotensin and/or of the enhancement of bradykinin on various steps of the insulin cascade signalling has been described as well an increase in GLUT4 glucose transporters after RAS inhibition. Furthermore, it has been demonstrated that angiotensin II inhibits adipogenic differentiation of human adipocytes via A1 receptors and, therefore, it has been hypothesised that RAS blockade may prevent diabetes by promoting the recruitment and differentiation of adipocytes. Finally, some lipophilic ARBs appear to induce PPAR-gamma activity in the adipose tissue. Hence, the protection against type 2 diabetes observed after RAS inhibition may be partially linked to a thiazolidinedione-like effect. In conclusion, numerous physiological and biochemical mechanisms could explain the protective effect of RAS inhibition against the development of type 2 diabetes in individuals with arterial hypertension or congestive heart failure. What might be the main mechanism in the overall protection effect of ACEIs or ARBs remains an open question.

Comparison of the effects of telmisartan and nifedipine gastrointestinal therapeutic system on blood pressure control, glucose metabolism, and the lipid profile in patients with type 2 diabetes mellitus and mild hypertension: a 12-month, randomized, double-blind study

BACKGROUND

Angiotensin receptor blockers (ARBs) provide effective blood pressure control. Whereas none of the ARBs appear to affect glucose homeostasis, some ARBs have been associated with a decrease in cholesterolemia.

OBJECTIVE

This study was conducted to evaluate blood pressure control glucose homeostasis, and the plasma lipid profile in patients with type 2 diabetes mellitus and mild hypertension during 12 months of treatment with the ARB telmisartan or nifedipine gastrointestinal therapeutic system (GITS).

METHODS

In this double-blind trial, patients taking oral hypoglycemic agents were randomized to receive telmisartan 40 mg or nifedipine GITS 20 mg once daily for 12 months. At the time of enrollment, patients were given advice on diet (1400-1600 kcal/d) and exercise (stationary bicycle for > or =30 min, 4 d/wk). Assessments of systolic blood pressure (SBP), diastolic blood pressure, body mass index (BMI), fasting plasma glucose concentrations, glycosylated hemoglobin, fasting plasma insulin concentrations, the homeostasis model assessment of insulin resistance, and the lipid profile were performed at baseline and after 6 and 12 months of treatment.

RESULTS

One hundred sixteen patients were divided into 2 age- and sex-matched treatment groups (58 men, 58 women; mean [SD] age, 52.5 [5] years). All patients were in good general health at baseline; had achieved adequate glycemic control with diet and oral hypoglycemic agents; were taking antihypercholesterolemic drugs; and had no evidence of macroangiopathy, microalbuminuria, or neuropathy. There were significant reductions from baseline in seated trough SBP after 12 months of treatment with both telmisartan and nifedipine GITS (from 139 [4] to 132 [4] mm Hg and from 140 [4] to 130 [4] mm Hg, respectively; both, P < 0.01). No change in BMI or glucose metabolism was observed with either treatment. After 12 months, there were significant improvements in concentrations of total cholesterol (TC) and low-density lipoprotein cholesterol (LDL-C) with telmisartan (-9% and -11.5%, respectively; both, P < 0.01) compared with nifedipine GITS (-2% and -1.5%).

CONCLUSIONS

In this selected sample of patients with type 2 diabetes and mild hypertension, both telmisartan and nifedipine GITS produced significant reductions in blood pressure. Telmisartan was associated with a slight but statistically significant improvement in plasma TC and LDL-C concentrations compared with nifedipine GITS.

Determinants of insulin sensitivity in chronic heart failure

OBJECTIVE

To describe the determinants of insulin sensitivity (IS) in chronic heart failure (CHF), we created a model in which the influence of lifestyle factors and etiology of heart failure on IS were incorporated concomitantly with age, left ventricular ejection fraction (LVEF) and parameters of body composition.

DESIGN

Observational cohort study.

SETTING

Outpatient clinic for chronic heart failure.

PATIENTS

Fifty-seven male CHF patients [NYHA class II-III, age 61+/-9 years, body mass index (BMI) 26.9+/-3.3 kg/m2 (mean+/-S.D.)].

INTERVENTIONS

Euglycemic hyperinsulinemic clamp, cycle ergometry, anthropometric measurements, LVEF and a physical activity questionnaire.

MAIN OUTCOME MEASURES

A model explaining the variance of IS in CHF.

RESULTS

IS was 18.2+/-8.6 microg.kg(-1).min(-1).mU(-1).l(-1), fasting insulin level was 15.9+/-11.0 mU/l and fasting glucose level was 5.5+/-0.6 mmol/l. Peak VO2 was 19.1+/-4.9 ml.kg(-1).min(-1) and LVEF 26.2+/-7.1%. IS was inversely associated with fasting insulin concentration (r=-0.50, P<0.001) and BMI (r=-0.54, P<0.001). After controlling for BMI, IS also revealed a correlation with age (r=-0.36, P<0.01). The model explained 60% of variance in IS: BMI contributed 20%, smoking 17%, age 17% and physical activity in daily life (DPA) 16% (all P<0.05) to the variance of IS, whereas LVEF (9%) and etiology of heart failure (8%) contributed moderately.

CONCLUSIONS

In CHF patients, IS is for a major part predicted by BMI, smoking, age, daily physical activity, LVEF and etiology of heart failure.

ACE inhibitor and angiotensin type I receptor antagonist in combination reduce renal damage in obese Zucker rats

BACKGROUND

In this study, we evaluated whether a combination of an angiotensin-converting enzyme (ACE) inhibitor, benazepril (B), with an angiotensin type I receptor antagonist (AT1RA), irbesartan (I), is as effective or more than drugs as monotherapy in controlling renal damage in obese Zucker rats (OZR), a model of metabolic syndrome.

METHODS

During six months, G1 (OZR receiving no treatment); G2 (OZR with B 10 mg/kg/day); G3 (OZR with I 50mg/kg/day); and G4 (OZR with B 5mg/kg/day + I 25 mg/kg/day). Kidneys were processed for light microscopy (LM) and immunohistochemistry, including antibodies against interstitial alpha-smooth-muscle-actin (alpha-SMA), plasminogen activator inhibitor-1 (PAI-1), transforming growth factor-beta(1)(TGF-beta 1), and collagen (COL) I, III, and IV.

RESULTS

All treated groups presented similar reduction in blood pressure compared with untreated OZR. However, animals from G4 (B + I) showed better control on proteinuria together with a higher creatinine clearance. Additionally, G4 showed a significant (P < 0.05) lower kidney weight; smaller glomerular area; lower glomerulosclerosis score; lower percentage of tubular atrophy, interstitial fibrosis, and interstitial alpha-SMA; lower tubular PAI-1 score; lower percentage of COL I, III, and IV in renal interstitium; and lower wall/lumen ratio in renal vessels, when compared with the other groups. OZR treated with B and/or I showed a better outcome (P < 0.01) in the carbohydrate and lipid metabolism in comparison with untreated OZR.

CONCLUSION

These results suggest that combined therapy using B and I is more effective than therapy with either drug at monotherapy for controlling renal damage in this animal model. In addition, data presented here reaffirm the benefit of interacting against renin-angiotensin-system (RAS) in the metabolic syndrome.

Peroxisome Proliferator Activator Receptors (PPAR), Insulin Resistance, and Cardiomyopathy

Diabetes is a risk factor for coronary atherosclerosis, myocardial infarction, and ischemic cardiomyopathy. Insulin resistance is associated with left ventricular (LV) hypertrophy and hypertensive cardiomyopathy. Even in the absence of coronary artery disease or hypertension, "diabetic cardiomyopathy" can develop because of myocardial autonomic dysfunction or impaired coronary flow reserve. The relationship between insulin resistance and cardiomyopathy is bidirectional. Systemic and myocardial glucose uptake is compromised in heart failure independent of etiology. These abnormalities are associated with cellular deficits of insulin signaling. Insulin resistance in heart failure can be detrimental, because transcriptional shifts in metabolic gene expression favor glucose over fat as a substrate for high-energy phosphate production. Although preexisting diabetes accelerates this process of "metabolic death," insulin resistance can also develop secondary to cardiomyopathy-associated overabundance of neurohormones and cytokines. Insulin resistance and fatty acid excess are potential therapeutic targets in heart failure, striving for efficient myocardial substrate utilization. Peroxisome proliferator activator receptor gamma (PPARgamma) agonists are antidiabetic agents with antilipemic and insulin-sensitizing activity. Experimental studies suggest salutary effects in limiting infarct size, attenuating myocardial reperfusion injury, inhibiting hypertrophic signaling and vascular antiinflammatory actions through cytokine inhibition. However, clinical applicability in diabetic patients experiencing heart failure has been hampered because of increased edema and even fewer reports of exacerbation associated with these compounds. Evidence to date argues for peripheral mechanisms of edema unrelated to central hemodynamics. Nevertheless, they are currently contraindicated in New York Heart Association (NYHA) III-IV patients, particularly in combination with insulin. Investigations are underway to decipher mechanisms, risks, and benefits of PPARgamma agonists, as well as the role of the structurally related PPARalpha receptor on cardiovascular metabolism and function.

Impact of the renin-angiotensin system on lipid and carbohydrate metabolism

PURPOSE OF REVIEW

This review is intended to provide an update of the impact of the renin-angiotensin system on lipid and carbohydrate metabolism and of its relationship with adipose-tissue and skeletal muscle activities.

RECENT FINDINGS

The components of the renin-angiotensin system are fully represented in the adipose tissue and appear to be upregulated in obesity--a condition associated with enhanced circulating angiotensinogen levels. The local renin-angiotensin system plays a role in adipocyte differentiation and possibly in body-fat accumulation. In humans, angiotensin II produced by mature adipocytes appears to inhibit the differentiation of adipocyte precursors, thus decreasing the percentage of small insulin-sensitive adipocytes. In turn, the lipid-storage capacity of adipose tissue could become reduced and triglycerides might accumulate in liver and skeletal muscle, contributing to insulin resistance. Randomized controlled trials indicating that pharmacological renin-angiotensin system blockade improves insulin sensitivity and reduces the risk of type 2 diabetes are in keeping with this possibility. The local renin-angiotensin system in skeletal muscle may affect exercise performance and the individual response to different types of muscular performance. The concept that the local renin-angiotensin system plays a role in body-fat storage and in lipid and carbohydrate metabolism is further supported by genetic studies showing that susceptibility to weight gain and possibly insulin resistance is greater in individuals carrying certain renin-angiotensin system allelic variants associated with alterations in systemic and local angiotensinogen levels and angiotensin-converting enzyme activity.

SUMMARY

In summary, the aforementioned data imply that the renin-angiotensin system plays a substantial role in obesity, insulin resistance and the associated increase in blood pressure.

Identification of telmisartan as a unique angiotensin II receptor antagonist with selective PPARgamma-modulating activity

The metabolic syndrome is a common precursor of cardiovascular disease and type 2 diabetes that is characterized by the clustering of insulin resistance, dyslipidemia, and increased blood pressure. In humans, mutations in the peroxisome proliferator-activated receptor-gamma (PPARgamma) have been reported to cause the full-blown metabolic syndrome, and drugs that activate PPARgamma have proven to be effective agents for the prevention and treatment of insulin resistance and type 2 diabetes. Here we report that telmisartan, a structurally unique angiotensin II receptor antagonist used for the treatment of hypertension, can function as a partial agonist of PPARgamma; influence the expression of PPARgamma target genes involved in carbohydrate and lipid metabolism; and reduce glucose, insulin, and triglyceride levels in rats fed a high-fat, high-carbohydrate diet. None of the other commercially available angiotensin II receptor antagonists appeared to activate PPARgamma when tested at concentrations typically achieved in plasma with conventional oral dosing. In contrast to ordinary antihypertensive and antidiabetic agents, molecules that can simultaneously block the angiotensin II receptor and activate PPARgamma have the potential to treat both hemodynamic and biochemical features of the metabolic syndrome and could provide unique opportunities for the prevention and treatment of diabetes and cardiovascular disease in high-risk populations.

Selective imidazoline agonist moxonidine plus the ACE inhibitor ramipril in hypertensive patients with impaired insulin sensitivity: partners in a successful MARRIAGE?

Hypertension in combination with clinically overt diabetes mellitus is recognized as a particularly powerful combination of risk factors that greatly increases cardiovascular vulnerability. There is also evidence that presumed pre-diabetic conditions such as insulin resistance, hyperinsulinaemia and compensatory hyperglycaemia may amplify overall cardiovascular risk in patients with hypertension, especially when encountered as part of the condition known as metabolic syndrome X (Reaven's syndrome). The long-term benefits of antihypertensive therapy may be compromised if these drugs exert adverse effects on metabolic parameters such as insulin sensitivity, or if they promote a transition from pre-diabetes to overt diabetes. Class differences in the effects of antihypertensives on metabolic indices may therefore be an important consideration when choosing treatment for patients who exhibit these characteristics. Experience from clinical trials suggests that drugs that target the renin-angiotensin system may have metabolic advantages over drugs such as beta-blockers and diuretics, but this conclusion has not been proved definitively. Moxonidine, which selectively targets imidazoline type-1 receptors in the sympathetic vasomotor centres of the rostral-ventrolateral medulla, is an effective antihypertensive and has been reported to exert favourable metabolic effects in preclinical and clinical studies. The MARRIAGE study (Moxonidine And Ramipril Regarding Insulin And Glucose Evaluation) will extend these preliminary observations by comparing the effects of moxonidine and the ACE inhibitor ramipril--and the combination of both drugs--on metabolic and haemodynamic parameters in patients with hypertension and impaired fasting glycaemia. A description is provided of the design and conduct of MARRIAGE.

Angiotensin and insulin resistance: conspiracy theory

Resistance to the metabolic effects of insulin is a contender for the short list of major cardiovascular risk factors. Since the elements of the syndrome of insulin resistance were first articulated together in 1988, numerous epidemiologic investigations and treatment endeavors have established a relationship between the metabolic disarray of impaired insulin action and cardiovascular disease. Angiotensin II, the primary effector of the renin-angiotensin system, has also achieved a place in the chronicles of cardiovascular risk factors. Conspiracy mechanisms by which angiotensin II and insulin resistance interact in the pathogenesis of cardiovascular disease are reviewed, with particular attention to recent developments in this engaging area of human research.