ACE inhibition and glucose transport in insulinresistant muscle: roles of bradykinin and nitric oxide

Hypertension in Patients with Insulin Resistance: Etiopathogenesis and Management in Children

Insulin resistance (IR) is a key component in the etiopathogenesis of hypertension (HS) in patients with diabetes mellitus (DM). Several pathways have been found to be involved in this mechanism in recent literature. For the above-mentioned reasons, treatment of HS should be specifically addressed in patients affected by DM. Two relevant recently published guidelines have stressed this concept, giving specific advice in the treatment of HS in children belonging to this group: the European Society of HS guidelines for the management of high blood pressure in children and adolescents and the American Academy of Pediatrics Clinical Practice Guideline for Screening and Management of High Blood Pressure in Children and Adolescents. Our aim is to summarize the main pathophysiological mechanisms through which IR causes HS and to highlight the specific principles of treatment of HS for children with DM.

Modulation of insulin resistance by renin angiotensin system inhibitors: implications for cardiovascular prevention

Insulin resistance (IR) and the related hyperinsulinamia play a key role in the genesis and progression of the continuum of cardiovascular (CV) disease. Thus, it is reasonable to pursue in primary and secondary CV prevention, the pharmacological strategies that are capable to interfere with the development of IR. The renin-angiotensin-aldosterone system (RAAS) plays an important role in the pathogenesis of IR. In particular, angiotensin II (Ang II) through the generation of reactive oxygen species, induces a low grade of inflammation, which impairs the insulin signal transduction. The angiotensin converting enzyme (ACE) inhibitors are effective not only as blood pressure-lowering agents, but also as modulators of metabolic abnormalities. Indeed, experimental evidence indicates that in animal models of IR, ACE inhibitors are capable to ameliorate the insulin sensitivity. The Ang II receptor blockers (ARBs) modulate the peroxisome proliferator-activated receptor (PPAR)-γ activity. PPARâ€"γ is a transcription factor that controls the gene expression of several key enzymes of glucose metabolism. A further mechanism that accounts for the favorable metabolic properties of ARBs is the capability to modulate the hypothalamicâ€"pituitary-adrenal (HPA) axis. The available clinical evidence is consistent with the concept that both ACE inhibitors and ARBs are able to interfere with the development of IR and its consequences like type 2 diabetes. In addition, pharmacological inhibition of the RAAS has favourable effects on dyslipidaemias, metabolic syndrome and obesity. Therefore, the pharmacological antagonism of the RAAS, nowadays, represents the first choice in the prevention of cardio-metabolic diseases.

ACE2 and energy metabolism: the connection between COVID-19 and chronic metabolic disorders

The renin-angiotensin system (RAS) has currently attracted increasing attention due to its potential function in regulating energy homeostasis, other than the actions on cellular growth, blood pressure, fluid, and electrolyte balance. The existence of RAS is well established in metabolic organs, including pancreas, liver, skeletal muscle, and adipose tissue, where activation of angiotensin-converting enzyme (ACE) - angiotensin II pathway contributes to the impairment of insulin secretion, glucose transport, fat distribution, and adipokines production. However, the activation of angiotensin-converting enzyme 2 (ACE2) - angiotensin (1-7) pathway, a novel branch of the RAS, plays an opposite role in the ACE pathway, which could reverse these consequences by improving local microcirculation, inflammation, stress state, structure remolding, and insulin signaling pathway. In addition, new studies indicate the protective RAS arm possesses extraordinary ability to enhance brown adipose tissue (BAT) activity and induces browning of white adipose tissue, and consequently, it leads to increased energy expenditure in the form of heat instead of ATP synthesis. Interestingly, ACE2 is the receptor of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which is threating public health worldwide. The main complications of SARS-CoV-2 infected death patients include many energy metabolism-related chronic diseases, such as diabetes. The specific mechanism leading to this phenomenon is largely unknown. Here, we summarize the latest pharmacological and genetic tools on regulating ACE/ACE2 balance and highlight the beneficial effects of the ACE2 pathway axis hyperactivity on glycolipid metabolism, as well as the thermogenic modulation.

Bradykinin B2 Receptor Signaling Increases Glucose Uptake and Oxidation: Evidence and Open Questions

The Kinin B2 receptor (B2R) is classically involved in vasodilation and inflammatory responses. However, through the observation of hypoglycemic effects of Angiotensin-I-Converting Enzyme (ACE) inhibitors, this protein has been related to metabolic glucose modulation in physiological and pathophysiological contexts. Although several studies have evaluated this matter, the different methodologies and models employed, combined with the distinct target organs, results in a challenge to summarize and apply the knowledge in this field. Therefore, this review aims to compile human and animal data in order to provide a big picture about what is already known regarding B2R and glucose metabolism, as well to suggest pending investigation issues aiming at evaluating the role of B2R in relation to glucose metabolism in homeostatic situations and metabolic disturbances. The data indicate that B2R signaling is involved mainly in glucose uptake in skeletal muscle and adipose tissue, acting as a synergic player beside insulin. However, most data indicate that B2R induces increased glucose oxidation, instead of storage, via activation of a broad signaling cascade involving Nitric Oxide (NO) and cyclic-GMP dependent protein kinase (PKG). Additionally, we highlight that this modulation is impaired in metabolic disturbances such as diabetes and obesity, and we provide a hypothetic mechanism to explain this blockade in light of literature data provided for this review, as well as other authors.

Comparison between calcium channel blocker with angiotensin converting enzyme inhibitor or angiotensin II type 1 receptor blocker combination on the development of new-onset diabetes in hypertensive Korean patients

Background and purpose

Rare comparative studies investigated the relationship between combination therapy of antihypertensive drugs and the incidence of new-onset diabetes mellitus (NODM). The aim of this study was to evaluate which combination therapy, calcium channel blocker (CCB) with angiotensin converting enzyme inhibitor (ACEI) or CCB with angiotensin II type 1 receptor blocker (ARB), is best in reducing/preventing the development of NODM during 4-year follow-up periods in non-diabetic hypertensive Korean patients.

Materials and methods

Finally, a total of 1221 consecutive hypertensive patients without a history of diabetes mellitus who had been prescribed CCB were retrospectively enrolled and divided into the two groups, an ACEI group (combination CCB with ACEI, n = 251) and an ARB group (combination CCB with ARB, n = 970). The primary endpoint was NODM, defined as a fasting blood glucose ≥126 mg/dL or hemoglobin A1c ≥ 6.5%. Secondary endpoint was major adverse cardiac events (MACE) defined as total death, non-fatal myocardial infarction (MI) and percutaneous coronary intervention (PCI).

Results

After propensity-score matched (PSM) analysis, two propensity-matched groups (243 pairs, n = 486, C-statistic = 0.696) were generated. During 4-year follow-up periods, there were similar incidence of NODM (Hazard ratio [HR]; 1.198, 95% confidence interval [CI]; 0.591-2.431, P = 0.616), MACE (HR; 1.324, 95% CI; 0.714-2.453, P = 0.373), total death, MI and PCI between the two groups after PSM analysis.

Conclusion

CCB with ACE or CCB with ARB combination strategies are equally acceptable in hypertensive Korean patients regarding the occurrence of NODM.

The Vasculature in Prediabetes

The frequency of prediabetes is increasing as the prevalence of obesity rises worldwide. In prediabetes, hyperglycemia, insulin resistance, and inflammation and metabolic derangements associated with concomitant obesity cause endothelial vasodilator and fibrinolytic dysfunction, leading to increased risk of cardiovascular and renal disease. Importantly, the microvasculature affects insulin sensitivity by affecting the delivery of insulin and glucose to skeletal muscle; thus, endothelial dysfunction and extracellular matrix remodeling promote the progression from prediabetes to diabetes mellitus. Weight loss is the mainstay of treatment in prediabetes, but therapies that improved endothelial function and vasodilation may not only prevent cardiovascular disease but also slow progression to diabetes mellitus.

Renal Denervation Reverses Hepatic Insulin Resistance Induced by High-Fat Diet

Activation of the sympathetic nervous system (SNS) constitutes a putative mechanism of obesity-induced insulin resistance. Thus, we hypothesized that inhibiting the SNS by using renal denervation (RDN) will improve insulin sensitivity (S_I) in a nonhypertensive obese canine model. S_I was measured using euglycemic-hyperinsulinemic clamp (EGC), before (week 0 [w0]) and after 6 weeks of high-fat diet (w6-HFD) feeding and after either RDN (HFD + RDN) or sham surgery (HFD + sham). As expected, HFD induced insulin resistance in the liver (sham 2.5 ± 0.6 vs. 0.7 ± 0.6 × 10^-4 dL ⋅ kg^-1 ⋅ min^-1 ⋅ pmol/L^-1 at w0 vs. w6-HFD [P < 0.05], respectively; HFD + RDN 1.6 ± 0.3 vs. 0.5 ± 0.3 × 10^-4 dL ⋅ kg^-1 ⋅ min^-1 ⋅ pmol/L^-1 at w0 vs. w6-HFD [P < 0.001], respectively). In sham animals, this insulin resistance persisted, yet RDN completely normalized hepatic S_I in HFD-fed animals (1.8 ± 0.3 × 10^-4 dL ⋅ kg^-1 ⋅ min^-1 ⋅ pmol/L^-1 at HFD + RDN [P < 0.001] vs. w6-HFD, [P not significant] vs. w0) by reducing hepatic gluconeogenic genes, including G6Pase, PEPCK, and FOXO1. The data suggest that RDN downregulated hepatic gluconeogenesis primarily by upregulating liver X receptor α through the natriuretic peptide pathway. In conclusion, bilateral RDN completely normalizes hepatic S_I in obese canines. These preclinical data implicate a novel mechanistic role for the renal nerves in the regulation of insulin action specifically at the level of the liver and show that the renal nerves constitute a new therapeutic target to counteract insulin resistance.

Angiotensin-II blockage, muscle strength, and exercise capacity in physically independent older adults

[Purpose] This study aimed to assess the exercise capacity and muscle strength in elderly people using drugs for angiotensin-II blockage. [Subjects and Methods] Four hundred and seven older adults were recruited for this study. Data about comorbidities and medication use were recorded and the individuals were divided into three groups: control group- elderly people with normal exercise capacity (n=235); angiotensin-converting enzyme inhibitor group - individuals using angiotensin-converting enzyme inhibitors (n=140); and angiotensin-II receptor blocker group- patients using angiotensin-II receptor blockers (n= 32). Exercise capacity was evaluated by a 6-minute walking test and muscle strength was measured using a handgrip dynamometer. [Results] Patients from the angiotensin-converting enzyme inhibitor group (mean: 99 ± 12%) and the angiotensin-II receptor blocker group (mean: 101 ± 14%) showed higher predicted values in the 6-minute walking test than the control group patients (mean: 96 ± 10%). Patients from the angiotensin-converting enzyme inhibitor group (mean: 105 ± 19%) and the angiotensin-II receptor blocker group (mean: 105.1 ± 18.73%) showed higher predicted values of muscle strength than control group patients (mean: 98.15 ± 18.77%). [Conclusion] Older adults using angiotensin-converting enzyme inhibitors or angiotensin-II receptor blockers have better functional exercise capacity and muscle strength.

The role of the renin-angiotensin system in the development of insulin resistance in skeletal muscle

The canonical renin-angiotensin system (RAS) involves the initial action of renin to cleave angiotensinogen to angiotensin I (ANG I), which is then converted to ANG II by the angiotensin converting enzyme (ACE). ANG II plays a critical role in numerous physiological functions, and RAS overactivity underlies many conditions of cardiovascular dysregulation. In addition, ANG II, by acting on both endothelial and myocellular AT1 receptors, can induce insulin resistance by increasing cellular oxidative stress, leading to impaired insulin signaling and insulin-stimulated glucose transport activity. This insulin resistance associated with RAS overactivity, when coupled with progressive ß-cell dysfunction, eventually leads to the development of type 2 diabetes. Interventions that target RAS overactivity, including ACE inhibitors, ANG II receptor blockers, and, most recently, renin inhibitors, are effective both in reducing hypertension and in improving whole-body and skeletal muscle insulin action, due at least in part to enhanced Akt-dependent insulin signaling and insulin-dependent glucose transport activity. ANG-(1-7), which is produced from ANG II by the action of ACE2 and acts via Mas receptors, can counterbalance the deleterious actions of the ACE/ANG II/AT1 receptor axis on the insulin-dependent glucose transport system in skeletal muscle. This beneficial effect of the ACE2/ANG-(1-7)/Mas receptor axis appears to depend on the activation of Akt. Collectively, these findings underscore the importance of RAS overactivity in the multifactorial etiology of insulin resistance in skeletal muscle, and provide support for interventions that target the RAS to ameliorate both cardiovascular dysfunctions and insulin resistance in skeletal muscle tissue.

Renin-angiotensin system blockers protect pancreatic islets against diet-induced obesity and insulin resistance in mice

Background

The associations between obesity, hypertension and diabetes are well established, and the renin-angiotensin system (RAS) may provide a link among them. The effect of RAS inhibition on type 2 diabetes is still unclear; however, RAS seems to play an important role in the regulation of the pancreas and glucose intolerance of mice fed high-fat (HF) diet.

Methods

C57BL/6 mice fed a HF diet (8 weeks) were treated with aliskiren (50 mg/kg/day), enalapril (30 mg/kg/day) or losartan (10 mg/kg/day) for 6 weeks, and the protective effects were extensively compared among groups by morphometry, stereological tools, immunostaining, Western blotting and hormonal analysis.

Results

All RAS inhibitors significantly attenuated the increased blood pressure in mice fed a HF diet. Treatment with enalapril, but not aliskiren or losartan, significantly attenuated body mass (BM) gain, glucose intolerance and insulin resistance, improved the alpha and beta cell mass and prevented the reduction of plasma adiponectin. Furthermore, enalapril treatment improved the protein expression of the pancreatic islet Pdx1, GLUT2, ACE2 and Mas receptors. Losartan treatment showed the greatest AT2R expression.

Conclusion

Our findings indicate that ACE inhibition with enalapril attenuated several of the deleterious effects of the HF diet. In summary, enalapril appears to be responsible for the normalization of islet morphology and function, of alpha and beta cell mass and of Pdx1 and GLUT2 expression. These protective effects of enalapril were attributed, primarily, to the reduction in body mass gain and food intake and the enhancement of the ACE2/Ang (1-7) /Mas receptor axis and adiponectin levels.

Diabetic cardiomyopathy: ongoing controversies in 2012

Diabetic cardiomyopathy is a controversial clinical entity that in its initial state is usually characterized by left ventricular diastolic dysfunction in patients with diabetes mellitus that cannot be explained by coronary artery disease, hypertension, or any other known cardiac disease. It was reported in up to 52-60% of well-controlled type-II diabetic subjects, but more recent studies, using standardized tissue Doppler criteria and more strict patient selection, revealed a much lower prevalence. The pathological substrate is myocardial damage, left ventricular hypertrophy, interstitial fibrosis, structural and functional changes of the small coronary vessels, metabolic disturbance, and autonomic cardiac neuropathy. Hyperglycemia causes myocardial necrosis and fibrosis, as well as the increase of myocardial free radicals and oxidants, which decrease nitric oxide levels, worsen the endothelial function, and induce myocardial inflammation. Insulin resistance with hyperinsulinemia and decreased insulin sensitivity may also contribute to the left ventricular hypertrophy. Clinical manifestations of diabetic cardiomyopathy may include dyspnea, arrhythmias, atypical chest pain, and dizziness. Currently, there is no specific treatment of diabetic cardiomyopathy that targets its pathophysiological substrate, but various therapeutic options are discussed that include improving diabetic control with both diet and drugs (metformin and thiazolidinediones), the use of ACE inhibitors, beta blockers, and calcium channel blockers. Daily physical activity and a reduction in body mass index may improve glucose homeostasis by reducing the glucose/insulin ratio and the increase of both insulin sensitivity and glucose oxidation by the skeletal and cardiac muscles.

Diabetic cardiomyopathy: understanding the molecular and cellular basis to progress in diagnosis and treatment

Diabetes mellitus is an important and prevalent risk factor for congestive heart failure. Diabetic cardiomyopathy has been defined as ventricular dysfunction that occurs in diabetic patients independent of a recognized cause such as coronary artery disease or hypertension. The disease course consists of a hidden subclinical period, during which cellular structural insults and abnormalities lead initially to diastolic dysfunction, later to systolic dysfunction, and eventually to heart failure. Left ventricular hypertrophy, metabolic abnormalities, extracellular matrix changes, small vessel disease, cardiac autonomic neuropathy, insulin resistance, oxidative stress, and apoptosis are the most important contributors to diabetic cardiomyopathy onset and progression. Hyperglycemia is a major etiological factor in the development of diabetic cardiomyopathy. It increases the levels of free fatty acids and growth factors and causes abnormalities in substrate supply and utilization, calcium homeostasis, and lipid metabolism. Furthermore, it promotes excessive production and release of reactive oxygen species, which induces oxidative stress leading to abnormal gene expression, faulty signal transduction, and cardiomyocytes apoptosis. Stimulation of connective tissue growth factor, fibrosis, and the formation of advanced glycation end-products increase the stiffness of the diabetic hearts. Despite all the current information on diabetic cardiomyopathy, translational research is still scarce due to limited human myocardial tissue and most of our knowledge is extrapolated from animals. This paper aims to elucidate some of the molecular and cellular pathophysiologic mechanisms, structural changes, and therapeutic strategies that may help struggle against diabetic cardiomyopathy.

Effect of Inhibition of Angiotensin-Converting Enzyme and/or Neutral Endopeptidase on Neuropathy in High-Fat-Fed C57Bl/6J Mice

We have demonstrated that treating diet-induced obese (DIO) mice with the vasopeptidase inhibitor ilepatril improved neural function. Vasopeptidase inhibitors block angiotensin-converting enzyme (ACE) and neutral endopeptidase (NEP) activity. We propose that increased activity of ACE and NEP contributes to pathophysiology of DIO. To address this issue C57Bl/6J mice or mice deficient in NEP were fed a high-fat diet and treated with ilepatril, enalapril, ACE inhibitor, or candoxatril, NEP inhibitor, using both prevention and intervention protocols. Endpoints included glucose utilization and neural function determination. In the prevention study glucose tolerance was impaired in DIO C57Bl/6J mice and improved with ilepatril or enalapril. Sensory nerve conduction velocity, thermal nociception, and intraepidermal nerve fiber density were impaired in DIO C57Bl/6J mice and improved with ilepatril or candoxatril. In the intervention study only enalapril improved glucose tolerance. Sensory nerve conduction velocity and intraepidermal nerve fiber density were improved by all three treatments, whereas thermal nociception was improved by ilepatril or candoxatril. In NEP-deficient mice DIO impaired glucose utilization and this was improved with enalapril. Nerve function was not impaired by DIO in NEP-deficient mice. These studies suggest that ACE and NEP play a role in pathophysiology associated with DIO.

Postexercise skeletal muscle glucose transport is normal in kininogen-deficient rats

A single exercise bout stimulates skeletal muscle glucose transport (GT) in the absence or presence of insulin. It has been suggested that the kallikrein-kinin system may contribute to exercise effects on both insulin-independent and insulin-dependent GT. Plasma kininogen, a key kallikrein-kinin system component, is a protein substrate for the enzyme kallikrein and the source of the peptide bradykinin.

PURPOSE

This study aimed to determine whether the postexercise (PEX) increase in insulin-dependent or insulin-independent GT is reduced in rats deficient in plasma kininogen versus normal rats.

METHODS

Male Brown Norway (BN) and Brown Norway Katholiek (BNK; plasma kininogen-deficient) rats were studied. BN and BNK rats were assigned to exercise (4×30-min swim) or sedentary (SED) groups. Rats were anesthetized immediately (0hPEX) or 3 h (3hPEX) after exercise. For 0hPEX and 0hSED rats, one epitrochlearis muscle per rat was used for AMPK phosphorylation and muscle glycogen analyses. The contralateral muscle was incubated with [H]-3-O-methylglucose (3-MG) for GT assay. For 3hPEX and 3hSED rats, one muscle from each rat was incubated without insulin, and the contralateral muscle was incubated with 60 μU·mL insulin, and both muscles were incubated with 3-MG for GT measurement.

RESULTS

For 0hPEX versus 0hSED, both BN and BNK rats had greater insulin-independent GT and AMPK phosphorylation with reduced glycogen after exercise. No genotype effects were found 0hPEX. There was a significant main effect of exercise (3hPEX>3hSED) and no interaction between exercise and genotype for basal or insulin-stimulated GT.

CONCLUSIONS

Plasma kininogen deficiency did not alter insulin-independent GT, AMPK phosphorylation, or glycogen depletion 0hPEX or insulin-dependent GT 3hPEX, suggesting that normal plasma kininogen is not essential for these important exercise effects.

Treatment of diabetic vasculopathy with rosiglitazone and ramipril: Hype or hope?

Cardiovascular diseases are responsible for increased morbidity and mortality in people with diabetes. Diabetic macrovasculopathy is associated with structural and functional changes in large arteries, which causes endothelial dysfunction, increased arterial stiffness, or decreased arterial distensability. Diabetic complications can be controlled and avoided by strict glycemic control, maintaining normal lipid profiles, regular physical exercise, adopting a healthy lifestyle and pharmacological interventions. Treatment goals for patients with type 2 diabetes specify targets for glycemia and other cardiometabolic risk factors, for example, hypertension and dyslipidemia. In recent years, special attention has been devoted to both thiazolidindiones (TZDs) and angiotensin converting enzyme (ACE) inhibitors as clinical trials revealed that these drugs may reduce the rate of progression to diabetes or delay the onset of diabetes, regression of impaired glucose tolerance (IGT) to normoglycemia and reduces the composite of all-cause mortality, nonfatal myocardial infarction and stroke in patients with diabetes. This review focuses on the potential roles of rosiglitazone, a member of TZD class of antidiabetic agents, and ramipril, an ACE inhibitor, in preventing the preclinical macrovasculopathy in diabetes and IGT population.

The B2 receptor of bradykinin is not essential for the post-exercise increase in glucose uptake by insulin-stimulated mouse skeletal muscle

Bradykinin can enhance skeletal muscle glucose uptake (GU), and exercise increases both bradykinin production and muscle insulin sensitivity, but bradykinin's relationship with post-exercise insulin action is uncertain. Our primary aim was to determine if the B2 receptor of bradykinin (B2R) is essential for the post-exercise increase in GU by insulin-stimulated mouse soleus muscles. Wildtype (WT) and B2R knockout (B2RKO) mice were sedentary or performed 60 minutes of treadmill exercise. Isolated soleus muscles were incubated with [³H]-2-deoxyglucose +/-insulin (60 or 100 microU/ml). GU tended to be greater for WT vs. B2RKO soleus with 60 microU/ml insulin (P=0.166) and was significantly greater for muscles with 100 microU/ml insulin (P<0.05). Both genotypes had significant exercise-induced reductions (P<0.05) in glycemia and insulinemia, and the decrements for glucose (approximately 14 %) and insulin (approximately 55 %) were similar between genotypes. GU tended to be greater for exercised vs. sedentary soleus with 60 microU/ml insulin (P=0.063) and was significantly greater for muscles with 100 microU/ml insulin (P<0.05). There were no significant interactions between genotype and exercise for blood glucose, plasma insulin or GU. These results indicate that the B2R is not essential for the exercise-induced decrements in blood glucose or plasma insulin or for the post-exercise increase in GU by insulin-stimulated mouse soleus muscle.

The sweeter side of ACE2: physiological evidence for a role in diabetes

Diabetes mellitus is a growing problem in all parts of the world. Both clinical trials and animal models of type I and type II diabetes have shown that hyperactivity of angiotensin-II (Ang-II) signaling pathways contribute to the development of diabetes and diabetic complications. Of clinical relevance, blockade of the renin-angiotensin system prevents new-onset diabetes and reduces the risk of diabetic complications. Angiotensin-converting enzyme (ACE) 2 is a recently discovered mono-carboxypeptidase and the first homolog of ACE. It is thought to inhibit Ang-II signaling cascades mostly by cleaving Ang-II to generate Ang-(1-7), which effects oppose Ang-II and are mediated by the Mas receptor. The enzyme is present in the kidney, liver, adipose tissue and pancreas. Its expression is elevated in the endocrine pancreas in diabetes and in the early phase during diabetic nephropathy. ACE2 is hypothesized to act in a compensatory manner in both diabetes and diabetic nephropathy. Recently, we have shown the presence of the Mas receptor in the mouse pancreas and observed a reduction in Mas receptor immuno-reactivity as well as higher fasting blood glucose levels in ACE2 knockout mice, indicating that these mice may be a new model to study the role of ACE2 in diabetes. In this review we will examine the role of the renin-angiotensin system in the physiopathology and treatment of diabetes and highlight the potential benefits of the ACE2/Ang-(1-7)/Mas receptor axis, focusing on recent data about ACE2.

Angiotensin-converting enzyme in skeletal muscle: sentinel of blood pressure control and glucose homeostasis

Recent evidence suggests a coordinated regulation by the local renin-angiotensin system (RAS) and tissue kallikrein-kinin system (TKKS) of blood flow and substrate supply in oxidative red myofibres of skeletal muscle tissue during endurance exercise. The performance of these myofibres is dependent on the increased oxidation of substrates facilitated by augmenting nutritive blood flow and glucose uptake. Humoral factors released by the contracting fibres, such as adenosine and kinins, are suggested to be responsible for this metabolic adjustment. The considerable drain of blood volume and the enormous consumption of glucose during endurance exercise require a control mechanism for the maintenance of blood pressure (BP) and glucose homeostasis. This is achieved by the sympathetic nervous system and its subordinate RAS, which is located in the nutritive vessels and parenchyma of the red myofibres. The angiotensin-converting enzyme (ACE) is the primary enzyme responsible for kinin degradation during exercise, underscoring the important interrelationship between the RAS and the TKKS in the critical role of kinins in the multifactorial regulation of muscle bioenergetics and glucose and BP homeostasis. Importantly, overactivity of the ACE, as occurs in individuals displaying risk factors such as overweight, causes exaggerated BP response and reduced glucose disposal. If they persist over years, compensatory responses to this ACE overactivity, such as hypersecretion of insulin and compliance of the vessel walls, will inevitably be exhausted, leading ultimately to the manifestation of type 2 diabetes and hypertension. This concept also provides a unifying explanation for the beneficial effects of ACE-inhibitors and Angiotensin II receptor antagonists in the treatment of hypertension and insulin resistance.

Treating hypertension while protecting the vulnerable islet in the cardiometabolic syndrome

Hypertension, a multifactorial-polygenic disease, interacts with multiple environmental stressors and results in functional and structural changes in numerous end organs, including the cardiovascular system. This can result in coronary heart disease, stroke, peripheral vascular disease, congestive heart failure, end-stage renal disease, insulin resistance, and damage to the pancreatic islet. Hypertension is the most important modifiable risk factor for major health problems encountered in clinical practice. Whereas hypertension was once thought to be a medical condition based on discrete blood pressure readings, a new concept has emerged defining hypertension as part of a complex and progressive metabolic and cardiovascular disease, an important part of a cardiometabolic syndrome. The central role of insulin resistance, oxidative stress, endothelial dysfunction, metabolic signaling defects within tissues, and the role of enhanced tissue renin-angiotensin-aldosterone system activity as it relates to hypertension and type 2 diabetes mellitus are emphasized. Additionally, this review focuses on the effect of hypertension on functional and structural changes associated with the vulnerable pancreatic islet. Various classes of antihypertensive drugs are reviewed, especially their roles in delaying or preventing damage to the vulnerable pancreatic islet, and thus delaying the development of type 2 diabetes mellitus.

Role of the renin-angiotensin system in age-related sarcopenia and diastolic dysfunction

The purpose of this review is to describe how recent pharmacological and genetic studies have contributed to our understanding of the role of the renin-angiotensin system (RAS) in age-related sarcopenia and diastolic dysfunction. Treatment strategies are limited in the context of both of these conditions, although interventions, which include blockade of the RAS (using angiotensin-converting enzyme inhibitors and angiotensin-receptor blockers) are successful and lead to improvements in functional outcomes that are not necessarily mediated by hemodynamic effects of the drugs. Studies in animal models of sarcopenia and diastolic dysfunction point to ubiquitous effects of RAS blockade on multiple biological mechanisms, including inflammation, oxidative damage and metabolic dysregulation. Therefore, a re-evaluation of the use of these drugs in other conditions should be considered for maintaining functional independence in older individuals.

ACE ID genotype affects blood creatine kinase response to eccentric exercise

Unaccustomed exercise may cause muscle breakdown with marked increase in serum creatine kinase (CK) activity. The skeletal muscle renin-angiotensin system (RAS) plays an important role in exercise metabolism and tissue injury. A functional insertion (I)/deletion (D) polymorphism in the angiotensin I-converting enzyme (ACE) gene (rs4646994) has been associated with ACE activity. We hypothesized that ACE ID genotype may contribute to the wide variability in individuals' CK response to a given exercise. Young individuals performed maximal eccentric contractions of the elbow flexor muscles. Pre- and postexercise CK activity was determined. ACE genotype was significantly associated with postexercise CK increase and peak CK activity. Individuals harboring one or more of the I allele had a greater increase and higher peak CK values than individuals with the DD genotype. This response was dose-dependent (mean +/- SE U/L: II, 8,882 +/- 2,362; ID, 4,454 +/- 1,105; DD, 2,937 +/- 753, ANOVA, P = 0.02; P = 0.009 for linear trend). Multivariate stepwise regression analysis, which included age, sex, body mass index, and genotype subtypes, revealed that ACE genotype was the most powerful independent determinant of peak CK activity (adjusted odds ratio 1.3, 95% confidence interval 1.03-1.64, P = 0.02). In conclusion, we indicate a positive association of the ACE ID genotype with CK response to strenuous exercise. We suggest that the II genotype imposes increased risk for developing muscle damage, whereas the DD genotype may have protective effects. These findings support the role of local RAS in the regulation of exertional muscle injury.

Genotype modulators of clinical severity in McArdle disease

The phenotypic manifestation of McArdle disease varies considerably from one individual to the next. The purpose of this study was to assess the possible association between the clinical severity of the disease, and each of the genotypes PYGM (R50X), ACE (I/D), AMPD1 (Q12X), PPARGC1A (G482S) and ACTN3 (R577X). We also assessed links between clinical disease severity and other potential phenotype modulators such as age or gender. McArdle disease was diagnosed in 99 patients of Spanish origin (60 male, 39 female; age range 8-81 years) by identifying the two mutant alleles of the PYGM gene. Disease severity was assessed using the grading scheme previously reported by Martinuzzi et al. [A. Martinuzzi, E. Sartori, M. Fanin, et al., Phenotype modulators in myophosphorylase deficiency, Ann. Neurol. 53 (2003) 497-502]. Significant correlation was observed (exact two-sided P<0.0001) between the number of D alleles of the ACE gene and the disease severity score. Rank-order correlation coefficients were 0.296 (95% CI: 0.169, 0.423) (Kendall's tau) and 0.345 (95% CI: 0.204, 0.486) (Somer's D). No significant relationships were detected between clinical severity and the remaining genotypes examined. Finally, disease severity was significantly worse in women with the disease. Our findings indicate that both ACE genotype and gender contribute to how McArdle disease manifests in an individual patient. The role of other candidate genes remains to be elucidated.

ACE inhibitors and angiotensin receptor antagonists and the incidence of new-onset diabetes mellitus: an emerging theme

The prevalence of type 2 diabetes mellitus continues to rise. Given the associated co-morbidities of obesity, hypertension and cardiovascular disease, the rising incidence of diabetes has important health consequences and efforts to reduce this incidence are critical. Although lifestyle modifications, including weight loss and exercise, are instrumental in the prevention of diabetes, pharmacological therapies that reduce the incidence of diabetes have the significant potential to lower risk. The results of several large clinical trials have demonstrated that treatment with ACE inhibitors and angiotensin receptor antagonists (angiotensin receptor blockers; ARBs) may prevent or delay the onset of diabetes. These trials have demonstrated an approximately 15-30% reduction in the new onset of diabetes in those receiving ACE inhibitors and ARBs when compared with placebo or other active therapy. Although the exact mechanism underlying the effects are not entirely clear, multiple animal and human studies have demonstrated that the renin-angiotensin system plays an important role in glucose homeostasis. Although future prospective studies to clarify the role of ACE inhibitors and ARBs in preventing diabetes are ongoing, there is substantial existing evidence from completed trials that these agents may prevent the onset of diabetes.

Inhalation of human insulin (exubera) augments the efficiency of muscle glucose uptake in vivo

This study assessed the site of increased glucose uptake resulting from insulin inhalation, quantified its effect under steady-state glucose concentrations, and identified the time to onset of effect. Human insulin was administered to 13 beagles via inhalation (Exubera [insulin human (rDNA origin)] Inhalation Powder; n = 7) or infusion into the inferior vena cava (Humulin R; n = 6) using an algorithm to match plasma insulin levels and kinetics for both groups. Somatostatin and glucagon were infused. Glucose was delivered into the portal vein (4 mg x kg(-1) x min(-1)) and a peripheral vein, as needed, to maintain arterial plasma glucose levels at 180 mg/dl. Hepatic exposure to insulin and glucose and liver glucose uptake were similar in both groups. Despite comparable arterial insulin and glucose levels, hind-limb glucose uptake increased 2.4-fold after inhalation compared with infusion due to increased muscle glucose uptake. Glucose infusion rate, nonhepatic glucose uptake, and tracer-determined glucose disposal were about twice as great compared with intravenous insulin. The effect appeared after 1 h, persisting at least as long as arterial insulin levels remained above basal. Pulmonary administration of insulin increases nonhepatic glucose uptake compared with infusion, and skeletal muscle is the likely site of that effect.

Bradykinin augments insulin-stimulated glucose transport in rat adipocytes via endothelial nitric oxide synthase-mediated inhibition of Jun NH2-terminal kinase

An increase in bradykinin has been suggested to contribute to the enhanced insulin sensitivity observed in the presence of ACE inhibitors. To investigate a potential direct, nonvascular effect on an insulin target tissue, the effect of bradykinin on glucose uptake and insulin signaling was studied in primary rat adipocytes. Whereas basal glucose uptake was not altered, bradykinin augmented insulin-stimulated glucose uptake twofold, which was blocked by HOE-140, a bradykinin B2 receptor antagonist. The bradykinin effect on glucose uptake was nitric oxide (NO) dependent, mimicked by NO donors and absent in adipocytes from endothelial NO synthase-/- mice. Investigation of insulin signaling revealed that bradykinin enhanced insulin receptor substrate-1 (IRS-1) Tyr phosphorylation, Akt/protein kinase B phosphorylation, and GLUT4 translocation. In contrast, insulin-stimulated extracellular signal-regulated kinase1/2 and Jun NH2-terminal kinase (JNK) activation were decreased in the presence of bradykinin, accompanied by decreased IRS-1 Ser307 phosphorylation. Furthermore, bradykinin did not enhance insulin action in the presence of the JNK inhibitor, SP-600125, or in adipocytes from JNK1-/- mice. These data indicate that bradykinin enhances insulin sensitivity in adipocytes via an NO-dependent pathway that acts by modulating the feedback inhibition of insulin signaling at the level of IRS-1.

Advanced-glycation end products in insulin-resistant states

Insulin resistance is a central component of a number of clinical conditions, including the metabolic syndrome, diabetes, and hypertension. There is emerging evidence that the consequent hyperinsulinemia and visceral adiposity may be directly responsible for the excess cardiovascular morbidity and mortality seen in these conditions. Advanced-glycation end products, a chemically diverse group of compounds found in higher levels in insulin-resistant states, have also been shown to adversely affect endothelial function as well as activate numerous intracellular signaling pathways implicated in the atherosclerotic pathway. In this review, we summarize the factors thought to be important in both the initiation and exacerbation of the insulin-resistant state, and directly examine the potential role of advanced-glycation end products in this process.

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.

Modulation of metabolic control by angiotensin converting enzyme (ACE) inhibition

Angiotensin converting enzyme (ACE) inhibitors are a widely used intervention for blood pressure control, and are particularly beneficial in hypertensive type 2 diabetic subjects with insulin resistance. The hemodynamic effects of ACE inhibitors are associated with enhanced levels of the vasodilator bradykinin and decreased production of the vasoconstrictor and growth factor angiotensin II (ATII). In insulin-resistant conditions, ACE inhibitors can also enhance whole-body glucose disposal and glucose transport activity in skeletal muscle. This review will focus on the metabolic consequences of ACE inhibition in insulin resistance. At the cellular level, ACE inhibitors acutely enhance glucose uptake in insulin-resistant skeletal muscle via two mechanisms. One mechanism involves the action of bradykinin, acting through bradykinin B(2) receptors, to increase nitric oxide (NO) production and ultimately enhance glucose transport. A second mechanism involves diminution of the inhibitory effects of ATII, acting through AT(1) receptors, on the skeletal muscle glucose transport system. The acute actions of ACE inhibitors on skeletal muscle glucose transport are associated with upregulation of insulin signaling, including enhanced IRS-1 tyrosine phosphorylation and phosphatidylinositol-3-kinase activity, and ultimately with increased cell-surface GLUT-4 glucose transporter protein. Chronic administration of ACE inhibitors or AT(1) antagonists to insulin-resistant rodents can increase protein expression of GLUT-4 in skeletal muscle and myocardium. These data support the concept that ACE inhibitors can beneficially modulate glucose control in insulin-resistant states, possibly through a NO-dependent effect of bradykinin and/or antagonism of ATII action on skeletal muscle.

The choice of antihypertensive drugs in patients with diabetes: angiotensin II and beyond

Affecting over 16 million individuals, diabetes mellitus is among the leading causes of mortality in the United States. Hypertension is a common finding among diabetic patients and increases their morbidity and mortality. Control of blood pressure in this population has been shown to improve outcomes. Recent randomized trials have proven the benefit of lower blood pressure goals in the treatment of hypertensive patients as compared with nondiabetic patients. Randomized controlled trials have also demonstrated that the selection of the antihypertensive agent used to treat hypertension in diabetic patients is as important as the reduction of blood pressure levels to the recommended levels. In this article, we first focus on the importance of the renin angiotensin system in the development of diabetic complications, and then we review the results of the recent studies that have had a major impact on the treatment of hypertension in diabetes.

Preventing diabetes by treating aspects of the metabolic syndrome

The metabolic syndrome often develops into and is usually present in type 2 diabetes in association with premature cardiovascular disease. Treating diabetes can prevent some of its devastating consequences, but it does not eliminate them all. With the goal to eliminate all the adverse consequences of the syndrome, the optimal approach would be through its prevention. Insulin resistance appears to be pivotal to development of the syndrome complex that includes features such as intra-abdominal or visceral obesity, hypertension, impaired glucose homeostasis, dyslipidemia with elevated triglycerides and low high-density lipoprotein without elevations of low-density lipoprotein, a procoagulant state, and impaired vascular function. Improving the insulin resistance needs to be the primary target of the therapy. Hyperglycemia, which is one feature of the metabolic syndrome, may range from impaired glucose tolerance (IGT) to overt diabetes. The risk of progression of the disease from IGT to diabetes is increased with time and the presence of various risk factors. Diabetes is a disease of serious concern because of the associated complication of the disease and the huge impact on the health care costs. Many short- and longer-term trials have shown promise in the prevention of diabetes and its metabolic and cardiovascular consequences.

Invited review: Effects of acute exercise and exercise training on insulin resistance

Insulin resistance of skeletal muscle glucose transport is a key defect in the development of impaired glucose tolerance and Type 2 diabetes. It is well established that both an acute bout of exercise and chronic endurance exercise training can have beneficial effects on insulin action in insulin-resistant states. This review summarizes the present state of knowledge regarding these effects in the obese Zucker rat, a widely used rodent model of obesity-associated insulin resistance, and in insulin-resistant humans with impaired glucose tolerance or Type 2 diabetes. A single bout of prolonged aerobic exercise (30-60 min at approximately 60-70% of maximal oxygen consumption) can significantly lower plasma glucose levels, owing to normal contraction-induced stimulation of GLUT-4 glucose transporter translocation and glucose transport activity in insulin-resistant skeletal muscle. However, little is currently known about the effects of acute exercise on muscle insulin signaling in the postexercise state in insulin-resistant individuals. A well-established adaptive response to exercise training in conditions of insulin resistance is improved glucose tolerance and enhanced skeletal muscle insulin sensitivity of glucose transport. This training-induced enhancement of insulin action is associated with upregulation of specific components of the glucose transport system in insulin-resistant muscle and includes increased protein expression of GLUT-4 and insulin receptor substrate-1. It is clear that further investigations are needed to further elucidate the specific molecular mechanisms underlying the beneficial effects of acute exercise and exercise training on the glucose transport system in insulin-resistant mammalian skeletal muscle.

Changes in blood glucose and plasma insulin levels induced by bradykinin in anaesthetized rats

1. The influence of bradykinin (BK) on blood glucose and plasma insulin levels was investigated in anaesthetized rats. 2. Blood glucose level was dose-dependently increased by intravenous infusion of BK. This effect of BK was enhanced by captopril, an inhibitor of angiotensin-converting enzyme (ACE). Des-Arg9-bradykinin (DABK), a kinin B1 receptor agonist, did not modify blood glucose levels while the effect of BK was inhibited by Hoe-140, a kinin B2 receptor antagonist. 3. The effect of BK was reduced by the NO-synthase inhibitor, N(omega)-nitro-L-arginine methyl ester (L-NAME), and by the cyclo-oxygenase inhibitor, indomethacin. The effect of BK was suppressed by the association of propranolol with phentolamine or phenoxybenzamine. It was also reduced by hexamethonium, a ganglion-blocking drug. In adrenalectomized rats, the infusion of BK slightly decreased blood glucose levels. 4. The hyperglycaemic effect of adrenaline was suppressed by propranolol associated with phentolamine or phenoxybenzamine, but it was not modified by L-NAME. 5. Infusion of BK did not modify plasma insulin levels. However, after phentolamine and propranolol, BK induced a transient 2 fold rise in plasma insulin levels. The release of insulin was dose-dependent and inhibited by Hoe-140. 6. We conclude that infusion of BK induces, via a stimulation of B2 receptors, the release of NO and of prostanoids. The latter agents activate through a reflex pathway the release of catecholamines from the adrenal medulla. This release increases blood glucose levels and reduces plasma insulin levels. After adrenoceptor inhibition, BK induces a secretion of insulin, via the stimulation of B2 receptors.

Acute effect of the dual angiotensin-converting enzyme and neutral endopeptidase 24-11 inhibitor mixanpril on insulin sensitivity in obese Zucker rat

The aim of this study was to determine whether acute dual angiotensin-converting enzyme (ACE)/neutral endopeptidase 24-11 (NEP) inhibition could improve whole body insulin-mediated glucose disposal (IMGD) more than ACE inhibition alone and whether this effect was mediated by the kinin-nitric oxide (NO) pathway activation. We therefore compared in anaesthetized obese (fa/fa) Zucker rats (ZOs) the effects of captopril (2 mg kg(-1), i.v.+2 mg kg(-1) h(-1)), retrothiorphan (25 mg kg(-1), i.v. +25 mg kg(-1) h(-1)), a selective NEP inhibitor, and mixanpril (25 mg kg(-1), i.v. +25 mg kg(-1) h(-1)), a dual ACE/NEP inhibitor, on IMGD using hyperinsulinaemic euglycaemic clamp technique. The role of the kinin-NO pathway in the effects of mixanpril was tested using a bradykinin B2 receptor antagonist (Hoe-140, 300 microg kg(-1)) and a NO-synthase inhibitor (N(omega)-nitro-L-arginine methyl ester, L-NAME, 10 mg kg(-1) i.v. +10 mg kg(-1) h(-1)) as pretreatments. Insulin sensitivity index (ISI) was lower in ZO controls than in lean littermates. Increases in ISI were observed in captopril- and retrothiorphan-treated ZOs. In mixanpril-treated ZOs, ISI was further increased, compared to captopril- and retrothiorphan-treated ZOs. In ZOs, Hoe-140 and L-NAME alone did not significantly alter and slightly reduced the ISI respectively. Hoe-140 and L-NAME markedly inhibited the ISI improvement induced by mixanpril. These results show that in obese insulin-resistant Zucker rats, under acute conditions, NEP or ACE inhibition can improve IMGD and that dual ACE/NEP inhibition improves IMGD more effectively than does either single inhibition. This effect is linked to an increased activation of the kinin-NO pathway.

Diabetes, hypertension, and cardiovascular disease: an update

Cardiovascular diseases (CVDs) are the major causes of mortality in persons with diabetes, and many factors, including hypertension, contribute to this high prevalence of CVD. Hypertension is approximately twice as frequent in patients with diabetes compared with patients without the disease. Conversely, recent data suggest that hypertensive persons are more predisposed to the development of diabetes than are normotensive persons. Furthermore, up to 75% of CVD in diabetes may be attributable to hypertension, leading to recommendations for more aggressive treatment (ie, reducing blood pressure to <130/85 mm Hg) in persons with coexistent diabetes and hypertension. Other important risk factors for CVD in these patients include the following: obesity, atherosclerosis, dyslipidemia, microalbuminuria, endothelial dysfunction, platelet hyperaggregability, coagulation abnormalities, and "diabetic cardiomyopathy." The cardiomyopathy associated with diabetes is a unique myopathic state that appears to be independent of macrovascular/microvascular disease and contributes significantly to CVD morbidity and mortality in diabetic patients, especially those with coexistent hypertension. This update reviews the current knowledge regarding these risk factors and their treatment, with special emphasis on the cardiometabolic syndrome, hypertension, microalbuminuria, and diabetic cardiomyopathy. This update also examines the role of the renin-angiotensin system in the increased risk for CVD in diabetic patients and the impact of interrupting this system on the development of clinical diabetes as well as CVD.

Renin-angiotensin system gene polymorphisms, blood pressure, dyslipidemia, and diabetes in Hong Kong Chinese: a significant association of tne ACE insertion/deletion polymorphism with type 2 diabetes

OBJECTIVE

In Chinese populations, hypertension is common and is a major risk factor for cerebrovascular and coronary heart disease, particularly when associated with diabetes. The clustering of these disorders and dyslipidemia and obesity is termed the metabolic syndrome and is increasing in prevalence in the populations of modernizing Asian nations. The renin-angiotensin system (RAS) helps maintain blood pressure and salt homeostasis and may play a role in the pathogenesis of aspects of the metabolic syndrome. We investigated three RAS gene polymorphisms--the ACE insertion/deletion (I/D), angiotensinogen (AGT) M235T, and angiotensin II type 1 receptor (AT1R) A1166C polymorphisms--for a possible role in modulating these disorders in 853 Chinese subjects with varying components of the metabolic syndrome.

RESEARCH DESIGN AND METHODS

The three gene polymorphisms of this cross-sectional study were detected using polymerase chain reaction-based protocols. The genotype frequencies were compared between the controls (n = 119) and both overlapping and nonoverlapping groups of patients with type 2 diabetes, hypertension, and dyslipidemia using chi2 test. Differences in levels of the biochemical parameters between the genotypes were determined using analysis of variance.

RESULTS

No significant relationship was identified between these polymorphisms and blood pressure in this population. Although the AT1RA1166C polymorphism was not associated with any aspect of the metabolic syndrome examined, there was limited evidence to suggest that the AGT M235T polymorphism may be associated with cholesterol levels. The ACE I allele was significantly more frequent in each group comprising subjects with type 2 diabetes/glucose intolerance (GIT), and the I allele was associated with higher fasting plasma glucose levels.

CONCLUSIONS

These findings suggest that these polymorphisms are unlikely to be involved in the pathogenesis of hypertension. The ACE I/D polymorphism was associated with the metabolic syndrome, having a higher frequency of I allele-containing genotypes in those groups, but this appeared to result predominantly from the relationship with type 2 diabetes/GIT in this population of Chinese subjects.

Effects of exercise training and ACE inhibition on insulin action in rat skeletal muscle

Our laboratory has demonstrated (Steen MS, Foianini KR, Youngblood EB, Kinnick TR, Jacob S, and Henriksen EJ, J Appl Physiol 86: 2044-2051, 1999) that exercise training and treatment with the angiotensin-converting enzyme (ACE) inhibitor trandolapril interact to improve insulin action in insulin-resistant obese Zucker rats. The present study was undertaken to determine whether a similar interactive effect of these interventions is manifest in an animal model of normal insulin sensitivity. Lean Zucker (Fa/-) rats were assigned to either a sedentary, trandolapril-treated (1 mg. kg(-1). day(-1) for 6 wk), exercise-trained (treadmill running for 6 wk), or combined trandolapril-treated and exercise-trained group. Exercise training alone or in combination with trandolapril significantly (P < 0.05) increased peak oxygen consumption by 26-32%. Compared with sedentary controls, exercise training alone or in combination with ACE inhibitor caused smaller areas under the curve for glucose (27-37%) and insulin (41-44%) responses during an oral glucose tolerance test. Exercise training alone or in combination with trandolapril also improved insulin-stimulated glucose transport in isolated epitrochlearis (33-50%) and soleus (58-66%) muscles. The increases due to exercise training alone or in combination with trandolapril were associated with enhanced muscle GLUT-4 protein levels and total hexokinase activities. However, there was no interactive effect of exercise training and ACE inhibition observed on insulin action. These results indicate that, in rats with normal insulin sensitivity, exercise training improves oral glucose tolerance and insulin-stimulated muscle glucose transport, whereas ACE inhibition has no effect. Moreover, the beneficial interactive effects of exercise training and ACE inhibition on these parameters are not apparent in lean Zucker rats and, therefore, are restricted to conditions of insulin resistance.