Captopril does not improve insulin action in essential hypertension: a double-blind placebo-controlled study

Effects on insulin action of adding low-dose thiazide to angiotensin-converting enzyme inhibitor in essential hypertension

Concern exists regarding adverse metabolic effects of antihypertensive agents. In the United States, diuretics are recommended first-line but additional agents, usually angiotensin-converting enzyme (ACE) inhibitors, are often required to meet blood pressure targets. We have previously shown that the combination of low-dose diuretic with an ACE inhibitor has detrimental effects on insulin action compared with ACE inhibitor alone in hypertensive type 2 diabetic patients. Our aim was to establish whether similar effects occur in nondiabetic hypertensive patients using this combination. A randomized double-blind placebo-controlled crossover design was used. After a 6-week run-in, when regular antihypertensive medications were withdrawn and placebo substituted, patients received captopril 50 mg twice daily with either bendroflumethiazide 1.25 mg (CB) or placebo (CP) for 12 weeks with a 6-week wash-out between treatments. Insulin action was assessed by hyperinsulinemic euglycemic clamp after the 6-week run-in and at the end of each treatment period. There were no differences between treatments in fasting glucose or insulin concentrations. Glucose infusion rates required to maintain euglycemia were the same with each treatment (CP 22.1±2.2 vs CB 22.2±2.2 μmol/kg per minute). There was no difference in endogenous glucose production in the basal state (CP 8.9±0.5 vs CB 9.5±0.7 μmol/kg per minute; P=0.23) or during hyperinsulinemia (CP 2.2±0.6 vs CB 1.5±0.3 μmol/kg per minute; P=0.30). In contrast to the situation in type 2 diabetes mellitus, ACE inhibitor combined with low-dose thiazide diuretic does not adversely affect insulin action when compared with ACE inhibitor alone in nondiabetic hypertensive patients.

The renin-angiotensin system in the pathophysiology of type 2 diabetes

Increased activation of the renin-angiotensin system (RAS) has been related to cardiovascular disease and type 2 diabetes mellitus. Most randomized clinical trials have demonstrated that RAS blockade reduces the incidence of type 2 diabetes, which has been explained by improved insulin secretion and insulin sensitivity. In this review, an overview of the mechanisms that may underlie the association between the RAS and type 2 diabetes will be provided, with focus on skeletal muscle and adipose tissue function. This will include discussion of several human studies performed in our laboratory to investigate the metabolic and hemodynamic effects of the RAS, combining in vivo measurements of whole-body and tissue metabolism with molecular and immunohistochemical approaches. Available data suggest that the detrimental effects of the RAS on insulin secretion are mediated by a reduction in pancreatic blood flow and induction of islet fibrosis, oxidative stress as well as inflammation, whereas both impaired skeletal muscle function and adipose tissue dysfunction may underlie RAS-induced insulin resistance. Thus, although future studies in humans are warranted, current evidence supports that targeting the RAS in intervention studies may improve metabolic and cardiovascular function in conditions of insulin resistance like obesity and type 2 diabetes.

Blood pressure lowering efficacy of angiotensin converting enzyme (ACE) inhibitors for primary hypertension

BACKGROUND

ACE inhibitors are widely prescribed for hypertension so it is essential to determine and compare their effects on blood pressure (BP), heart rate and withdrawals due to adverse effects (WDAE).

OBJECTIVES

To quantify the dose-related systolic and/or diastolic BP lowering efficacy of ACE inhibitors versus placebo in the treatment of primary hypertension.

SEARCH STRATEGY

We searched CENTRAL (The Cochrane Library 2007, Issue 1), MEDLINE (1966 to February 2007), EMBASE (1988 to February 2007) and reference lists of articles.

SELECTION CRITERIA

Double-blind, randomized, controlled trials evaluating the BP lowering efficacy of fixed-dose monotherapy with an ACE inhibitor compared with placebo for a duration of 3 to 12 weeks in patients with primary hypertension.

DATA COLLECTION AND ANALYSIS

Two authors independently assessed the risk of bias and extracted data. Study authors were contacted for additional information. WDAE information was collected from the trials.

MAIN RESULTS

Ninety two trials evaluated the dose-related trough BP lowering efficacy of 14 different ACE inhibitors in 12 954 participants with a baseline BP of 157/101 mm Hg. The data do not suggest that any one ACE inhibitor is better or worse at lowering BP. A dose of 1/8 or 1/4 of the manufacturer's maximum recommended daily dose (Max) achieved a BP lowering effect that was 60 to 70% of the BP lowering effect of Max. A dose of 1/2 Max achieved a BP lowering effect that was 90% of Max. ACE inhibitor doses above Max did not significantly lower BP more than Max. Combining the effects of 1/2 Max and higher doses gives an estimate of the average trough BP lowering efficacy for ACE inhibitors as a class of drugs of -8 mm Hg for SBP and -5 mm Hg for DBP. ACE inhibitors reduced BP measured 1 to 12 hours after the dose by about 11/6 mm Hg.

AUTHORS' CONCLUSIONS

There are no clinically meaningful BP lowering differences between different ACE inhibitors. The BP lowering effect of ACE inhibitors is modest; the magnitude of trough BP lowering at one-half the manufacturers' maximum recommended dose and above is -8/-5 mm Hg. Furthermore, 60 to 70% of this trough BP lowering effect occurs with recommended starting doses. The review did not provide a good estimate of the incidence of harms associated with ACE inhibitors because of the short duration of the trials and the lack of reporting of adverse effects in many of the trials.

Effect of short-term ACE inhibitor treatment on peripheral insulin sensitivity in obese insulin-resistant subjects

AIMS/HYPOTHESIS

This study was designed to investigate the effect of short-term ACE inhibitor treatment on insulin sensitivity and to examine possible underlying metabolic and haemodynamic effects in obese insulin-resistant subjects.

METHODS

A randomised, double-blind placebo-controlled trial was performed in 18 obese insulin-resistant men (age, 53 +/- 2 years; BMI, 32.6 +/- 0.8 kg/m(2); homeostasis model assessment of insulin resistance, 5.6 +/- 0.5; systolic blood pressure [SBP], 140.8 +/- 3.2; diastolic blood pressure [DBP], 88.8 +/- 1.6 mmHg), who were free of any medication. The aim was to examine the effects of 2 weeks of ACE inhibitor treatment (ramipril, 5 mg/day) on insulin sensitivity, forearm blood flow, substrate fluxes across the forearm, whole-body substrate oxidation and intramuscular triacylglycerol (IMTG) content.

RESULTS

Ramipril treatment decreased ACE activity compared with placebo (-22.0 +/- 1.7 vs 0.2 +/- 1.1 U/l, respectively, p < 0.001), resulting in a significantly reduced blood pressure (SBP, -10.8 +/- 2.1 vs -2.7 +/- 2.0 mmHg, respectively, p = 0.01; DBP, -10.1 +/- 1.3 vs -4.2 +/- 2.1 mmHg, respectively, p = 0.03). Ramipril treatment had no effect on whole-body insulin-mediated glucose disposal (before: 17.9 +/- 2.0, after: 19.1 +/- 2.4 micromol kg body weight(-1) min(-1), p = 0.44), insulin-mediated glucose uptake across the forearm (before: 1.82 +/- 0.39, after: 1.92 +/- 0.29 micromol 100 ml forearm tissue(-1) min(-1), p = 0.81) and IMTG content (before: 45.4 +/- 18.8, after: 48.8 +/- 27.5 micromol/mg dry muscle, p = 0.92). Furthermore, the increase in carbohydrate oxidation (p < 0.001) and forearm blood flow (p < 0.01), and the decrease in fat oxidation (p < 0.001) during insulin stimulation were not significantly different between treatments.

CONCLUSIONS/INTERPRETATION

Short-term ramipril treatment adequately reduced ACE activity and blood pressure, but had no significant effects on insulin sensitivity, forearm blood flow, substrate fluxes across the forearm, whole-body substrate oxidation and IMTG content in obese insulin-resistant subjects.

Diabetes, prediabetes, and cardiovascular risk: shifting the paradigm

As the prevalence of diabetes continues to increase worldwide, diabetes-related macrovascular morbidity and mortality are becoming major health care problems. Epidemiologic evidence suggests this relationship begins early in the progression from normal glucose tolerance to frank diabetes. This report reviews this epidemiologic evidence linking early stages of glucose dysregulation with cardiovascular disease and discusses the results of major clinical trials demonstrating that lifestyle or pharmacologic intervention can reduce the incidence of diabetes in high-risk individuals. These observations indicate that early identification and aggressive treatment of subjects with impaired fasting glucose or impaired glucose tolerance have the potential to reduce both the incidence of diabetes and its related cardiovascular disease. Three clinical trials are being conducted to test whether early pharmacotherapy can reduce or delay the incidence of diabetes, and their results may well begin to shift the treatment paradigm toward earlier intervention.

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.

Pathophysiological implications of insulin resistance on vascular endothelial function

BACKGROUND

Insulin resistance is a key component of the insulin resistance syndrome and is a crucially important metabolic abnormality in Type 2 diabetes. Insulin-resistant individuals are at significantly increased risk of cardiovascular disease, although the underlying mechanisms remain incompletely understood. The endothelium is thought to play a critical role in maintaining vascular homeostasis, a process dependent on the balance between the production of nitric oxide, superoxide and other vasoactive substances. Endothelial dysfunction has been demonstrated in insulin-resistant states in animals and humans and may represent an important early event in the development of atherosclerosis. Insulin resistance may be linked to endothelial dysfunction by a number of mechanisms, including disturbances of subcellular signalling pathways common to both insulin action and nitric oxide production. Other potential unifying links include the roles of oxidant stress, endothelin, the renin angiotensin system and the secretion of hormones and cytokines by adipose tissue. Lifestyle measures and drug therapies which improve insulin sensitivity and ameliorate endothelial dysfunction may be important in delaying the progression to overt cardiovascular disease in at risk individuals.

METHODS

We conducted a literature search using Medline, restricted to articles published in the English language between 1966 and the present, and reviewed bibliographies of relevant articles. An initial search strategy employing combinations of the MeSH terms: insulin resistance; endothelium, vascular; insulin; nitric oxide or hyperinsulinaemia produced over 300 references. Focused searches using keywords relevant to the molecular aspects of endothelial function and insulin signalling, and lifestyle or pharmacological interventions relevant to insulin resistance or endothelial function, produced over 300 further references. Abstracts of all references were screened before selecting those relevant to this review.

Influence of captopril on symptomatic and hormonal responses to hypoglycaemia in humans

AIMS

Hypoglycaemic symptoms and hormonal counter-regulation are of high importance to avoid the risk of severe hypoglycaemia in patients with diabetes mellitus. Various antihypertensive drugs, such as angiotensin-converting enzyme (ACE) inhibitors, have been suspected for a long time to reduce this response to hypoglycaemia in diabetic subjects. Although ACE inhibitors are approved for controlling diabetic complications, previous investigations regarding this putative side-effect are controversial.

METHODS

We performed clamp experiments in 16 healthy men lasting for 6 h each. The subjects were pretreated for 7 days with captopril 3 x 25 mg day-1 vs placebo in a randomized, double-blind, crossover study. Plasma glucose was decreased in a stepwise manner during a hypoglycaemic clamp session and counter-regulatory hormones [epinephrine (adrenaline), norepinephrine (adrenaline), ACTH, cortisol, glucagon], symptoms, and haemodynamic parameters (blood pressure, heart rate] were measured.

RESULTS

Counter-regulatory hormone concentrations significantly increased in both sessions (ACE inhibitor vs placebo) during hypoglycaemia. The rise of counter-regulatory hormones as well as symptom scores were equal under both ACE inhibitor and placebo treatment. Systolic blood pressure and heart rate increased (from 110 +/- 3 vs 115 +/- 3 mmHg to 132 +/- 4 vs 133 +/- 4 mmHg) whereas diastolic blood pressure slightly decreased (from 63 +/- 2 vs 70 +/- 3 mmHg to 61 +/- 2 vs 64 +/- 2 mmHg) independent of pretreatment. Systolic and diastolic blood pressure were significantly lower in the captopril session vs placebo (P < 0.05).

CONCLUSIONS

Our results demonstrate that subchronic treatment with captopril does not attenuate symptomatic and hormonal response to hypoglycaemia. Thus, to patients at risk of hypoglycaemia who require antihypertensive or nephroprotective treatment, we would continue giving an ACE inhibitor.

ACE inhibitor improves insulin resistance in diabetic mouse via bradykinin and NO

Improvement of insulin resistance by ACE inhibitors has been suggested; however, this mechanism has not been proved. We postulated that activation of the bradykinin-nitric oxide (NO) system by an ACE inhibitor enhances glucose uptake in peripheral tissues by means of an increase in translocation of glucose transporter 4 (GLUT4), resulting in improvement of insulin resistance. Administration of an ACE inhibitor, temocapril, significantly decreased plasma glucose and insulin concentrations in type 2 diabetic mouse KK-Ay. Mice treated with temocapril showed a smaller plasma glucose increase after glucose load. We demonstrated that temocapril treatment significantly enhanced 2-[3H]-deoxy-D-glucose (2-DG) uptake in skeletal muscle but not in white adipose tissue. Administration of a bradykinin B2 receptor antagonist, Hoe140, or an NO synthase inhibitor, L-NAME, attenuated the enhanced glucose uptake by temocapril. Moreover, we observed that translocation of GLUT4 to the plasma membrane was significantly enhanced by temocapril treatment without influencing insulin receptor substrate-1 phosphorylation. In L6 skeletal muscle cells, 2-DG uptake was increased by temocaprilat, and Hoe140 inhibited this effect of temocaprilat but not that of insulin. These results suggest that temocapril would improve insulin resistance and glucose intolerance through increasing glucose uptake, especially in skeletal muscle at least in part through enhancement of the bradykinin-NO system and consequently GLUT4 translocation.