Predictors of renal and cardiovascular mortality in patients with non-insulin-dependent diabetes: a brief overview of microalbuminuria and insulin resistance

Review: Renin-angiotensin-aldosterone system intervention in the cardiometabolic syndrome and cardio-renal protection

The metabolic syndrome, also known as the cardiometabolic syndrome (CMS), is a state of metabolic and vascular dysregulation that is associated with activation of the renin-angiotensin-aldosterone system (RAAS). Clinical components of the CMS include central or visceral obesity, hypertension (HTN), dyslipidemia, insulin resistance/hyperinsulinemia, and microalbuminuria that collectively convey increases in oxidative stress, inflammation, and subsequent endothelial dysfunction. The cardio-renal inflammation and oxidative stress enhanced in the CMS increases the risk for cardiovascular disease (CVD) and renal disease end-points such as stroke, congestive heart failure, and chronic kidney disease (CKD). The development of proteinuria is known to herald progressive kidney disease (e.g. CKD) and both are now well accepted as CVD risk factors. Evidence suggests a role for visceral obesity, insulin resistance/hyperinsulinemia, HTN, and other components of the CMS lead to an increased risk for proteinuria and progressive loss of renal function. Intervention with agents that block the RAAS (e.g. ACE inhibitors and Angiotensin type 1 receptor blockers) have been shown to reduce proteinuria, CKD progression, and CVD events. Herein, we will examine the relationship between RAAS intervention and reductions in CKD and CVD events.

The kidney in acromegaly: renal structure and function in patients with acromegaly during active disease and 1 year after disease remission

BACKGROUND

The GH/insulin-like growth factor 1 axis is physiologically involved in the regulation of electrolytes and water homeostasis by kidneys, and influences glomerular filtration and tubular re-absorption processes. The aim of the study was to investigate renal structure and function in acromegalic patients during active disease and disease remission.

PATIENTS

Thirty acromegalic patients (15 males and 15 females), aged 32-70 years, were enrolled for the study. Ten de novo patients had active disease, whereas 20 patients showed disease remission 1 year after medical treatment with somatostatin analogs (SA) (ten patients) or surgery (ten patients). Thirty healthy subjects matched for age, gender, and body surface area were enrolled as controls.

RESULTS

In both active (A) and controlled (C) patients, creatinine clearance (P<0.001) and citrate (P<0.05) and oxalate levels (P<0.001) were higher, whereas filtered Na (P<0.001) and K (P<0.001) fractional excretions were lower than those in the controls. Urinary Ca (P<0.001) and Ph (P<0.05) levels were significantly increased compared with the controls, and in patients with disease control, urinary Ca (P<0.001) levels were significantly reduced compared with active patients. Microalbuminuria was significantly increased in active patients (P<0.05) compared with controlled patients and healthy control subjects. The longitudinal (P<0.05) and transverse (P<0.05) diameters of kidneys were significantly higher than those in the controls. In all patients, the prevalence of micronephrolithiasis was higher than that in the controls (P<0.001), and was significantly correlated to disease duration (r=0.871, P<0.001) and hydroxyproline values (r=0.639, P<0.001).

CONCLUSIONS

The results of the current study demonstrated that acromegaly affects both renal structure and function. The observed changes are not completely reversible after disease remission.

Microalbuminuria in insulin sensitivity in patients with growth hormone-secreting pituitary tumor

CONTEXT

Impaired glucose tolerance and diabetes mellitus are frequently present in acromegalic patients in whom the degree of impaired glucose metabolism seems directly correlated with GH levels. Microalbuminuria is reported to be directly correlated with insulin resistance, and both conditions predict cardiovascular disease mortality.

OBJECTIVE

Our objective was to investigate the microalbuminuria levels as a marker of endothelial dysfunction in acromegalic patients.

DESIGN

We conducted an observational, multicenter, open prospective study.

SUBJECTS

Subjects included 74 patients with active acromegaly (52 with normal glucose tolerance, 16 with impaired glucose tolerance, and six with diabetes), and 50 healthy subjects matched for age, gender, and body mass index were studied as controls.

RESULTS

In the whole group, mean GH and IGF-I levels were 24.2+/-3.9 ng/ml and 700.1+/-23.0 microg/liter, respectively. The insulin sensitivity index (ISI) in the patients was lower than in the controls (P<0.0005). In impaired glucose tolerance and diabetic patients, microalbuminuria was higher than in normal glucose tolerance patients (P<0.05 and P<0.0005 respectively). Hypertensive patients had higher levels of microalbuminuria than normotensive ones (P<0.005). The levels of microalbuminuria related to creatinine were directly correlated with fasting glucose levels (r=0.27; P=0.0019), fasting insulin levels (r=0.28; P=0.017), and insulin after 90 (r=0.26; P=0.027) and 120 min after glucose load (r=0.26; P=0.023) and indirectly correlated with ISI composite (P<0.0001; r=-0.48). By a multivariate analysis, the log-ISI composite was the strongest predictor of microalbuminuria (t=-3.19; P=0.0021).

CONCLUSIONS

Impairment of glucose tolerance in acromegaly is associated with high levels of microalbuminuria. For this reason, microalbuminuria should be part of cardiovascular risk assessment in these patients.

Obesity, cardiometabolic syndrome, and chronic kidney disease: the weight of the evidence

The epidemic of obesity experienced in both industrialized and nonindustrialized countries largely accounts for the increase in the prevalence of the cardiometabolic syndrome (CMS). Obesity and the CMS significantly increase the risk for cardiovascular disease (CVD) and chronic kidney disease (CKD). Multiple abnormalities that can lead to kidney injury have been identified in overweight and obese people, including insulin resistance, compensatory hyperinsulinemia, inappropriate activation of the renin-angiotensin-aldosterone system and increased oxidative stress, endoplasmic reticulum stress, coagulability, and impaired fibrinolysis. The combined effects of these conditions induce in the kidneys impaired pressure natriuresis, glomerular hypertension, endothelial dysfunction, and vasoconstriction, as well as matrix proliferation and expansion. Among the consequences are microalbuminuria, now known to be a surrogate of diffuse endothelial dysfunction as well as a predictor of CVD, and CKD. Diet and regular physical activity are the cornerstones of weight management, and they add to currently available pharmacologic agents and bariatric surgery. The understanding of the pathophysiology of obesity/CMS helps to explain the benefits of agents that improve insulin sensitivity, control inflammation, and block the renin-angiotensin-aldosterone system. The increasing prevalence of obesity and CMS contribute to the growing frequency of CKD and demands the development of multifactorial strategies directed at identifying people at risk, as well as preventing excessive weight gain and its deleterious consequences.

Effects of melatonin and zinc on lipid profile and renal function in type 2 diabetic patients poorly controlled with metformin

Glycemic control and prevention of secondary complications are the most important goals of using pharmacologic treatment of diabetes mellitus (DM). The inadequate responses to oral hypoglycemic agents may be attributed to inadequate postreceptor events even when insulin levels are quite sufficient, and associated with oxidative stress induced by long-term hyperglycemia. The administration of antioxidants such as melatonin and zinc may improve tissue responses to insulin and increase the efficacy of drugs, e.g. metformin, which act through this pathway. This project was designed to evaluate the effects of melatonin and zinc on the lipid profile and renal function in type 2 DM patients poorly controlled with metformin. A placebo-controlled, double-blind clinical trial was performed in which 46 type 2 diabetic patients were selected and allocated into three groups. These groups were treated with single daily oral doses of both 10 mg of melatonin and 50 mg of zinc acetate alone: 10 mg of melatonin and 50 mg of zinc acetate in addition to the regularly used metformin or placebo, given at bedtime for 90 days. Fasting lipid profiles and microalbuminuria (MAU) were measured before initiating the treatments (zero time) and after 30 and 90 days of treatment. Daily administration of melatonin and zinc improved the impaired lipid profile and decreased the level of MAU; the addition of this treatment regimen in combination with metformin improved the tissue responses to this oral hypoglycemic agent. In conclusion, the combination of melatonin and zinc acetate, when used alone or in combination with metformin, improves DM-related complications such as the impaired lipid profile and MAU in type 2 DM patients.

High dietary sucrose triggers hyperinsulinemia, increases myocardial β-oxidation, reduces glycolytic flux and delays post-ischemic contractile recovery

Although the causal relationship between insulin resistance (IR) and hypertension is not fully resolved, the importance of IR in cardiovascular dysfunction is recognized. As IR may follow excess sucrose or fructose diet, the aim of this study was to test whether dietary starch substitution with sucrose results in myocardial dysfunction in energy substrate utilization and contractility during normoxic and post-ischemic conditions. Forty-eight male Wistar rats were randomly allocated to three diets, differing only in their starch to sucrose (S) ratio (13, 2 and 0 for the Low S, Middle S and High S groups, respectively), for 3 weeks. Developed pressure and rate x pressure product (RPP) were determined in Langendorff mode-perfused hearts. After 30 min stabilization, hearts were subjected to 25 min of total normothermic global ischemia, followed by 45-min reperfusion. Oxygen consumption, beta-oxidation rate (using 1-13C hexanoate and Isotopic Ratio Mass Spectrometry of CO2 produced in the coronary effluent) and flux of non-oxidative glycolysis were also evaluated. Although fasting plasma glucose levels were not affected by increased dietary sucrose, high sucrose intake resulted in increased plasma insulin levels, without significant rise in plasma triglyceride and free fatty acid concentrations. Sucrose-rich diet reduced pre-ischemic baseline measures of heart rate, RPP and non-oxidative glycolysis. During reperfusion, post-ischemic recovery of RPP was impaired in the Middle S and High S groups, as compared to Low S, mainly due to delayed recovery of developed pressure, which by 45 min of reperfusion eventually resumed levels matching Low S. At the start of reperfusion, delayed post-ischemic recovery of contractile function was accompanied by: (i) reduced lactate production; (ii) decreased lactate to pyruvate ratio; (iii) increased beta-oxidation; and (iv) depressed metabolic efficiency. In conclusion, sucrose rich-diet increased plasma insulin levels, in intact rat, and increased cardiac beta-oxidation and coronary flow-rate, but reduced glycolytic flux and contractility during normoxic baseline function of isolated perfused hearts. Sucrose rich-diet impaired early post-ischemic recovery of isolated heart cardiac mechanical function and further augmented cardiac beta-oxidation but reduced glycolytic and lactate flux.

Cardiometabolic syndrome and chronic kidney disease

Chronic kidney disease (CKD) is increasingly recognized as a major risk factor for end-stage renal disease (ESRD), cardiovascular (CV) disease, and CV-related premature death. More than 8 million people in the United States have CKD; therefore, preventive stratiegies should be directed at identifying risk factors for this condition. There is growing evidence implicating the cardiometabolic syndrome, a clustering of CV risk factors that include obesity, insulin resistance, compensatory hyperinsulinemia, dysglycemia, atherogenic dyslipidemia, and hypertension. Factors mediating this relationship include increased glomerular filtration, increased vascular permeability, oxidative and endoplasmic reticulum stress, activation of the renin-angiotensin system, and inappropriate secretion of growth factors. The consequences are microalbuminuria, a marker of inflammation and endothelial dysfunction, renal vascular proliferation, extracellular matrix expansion, and CKD. Prevention of CKD should be directed at controlling all components of the cardiometabolic syndrome, with the ultimate goal of reducing the burden imposed by ESRD.

Improving macrovascular outcomes in type 2 diabetes: Outcome studies in cardiovascular risk and metabolic control

BACKGROUND

Type 2 diabetes is accompanied by a host of potentially modifiable cardiovascular disease risk factors. Consequently, people with type 2 diabetes have a higher risk of macrovascular disease than the non-diabetic population, and a poor prognosis following an event. Several large-scale primary and secondary outcome studies have included large diabetes subgroups for post-hoc analysis, and a limited number of studies have focused specifically on type 2 diabetes.

SCOPE

This review provides an overview of macrovascular outcome studies in type 2 diabetes and discusses potential new targets for therapy based upon a MEDLINE literature search from January 1990 to April 2006.

FINDINGS

Large cardiovascular outcome studies show that treating cardiovascular disease risk factors significantly reduces the risk of primary and secondary macrovascular events in patients with type 2 diabetes. The evidence for targeting hypertension (using renin-angiotensin system inhibitors), dyslipidemia (statins), and coagulation factors (aspirin) appears robust. However, the macrovascular benefits of improved glucose control remain to be proven definitively, although metformin may have advantages over other glucose-lowering agents. Nevertheless, these studies reveal that significant excess residual risk remains, highlighting the need for new therapies. It is also apparent that some agents (e.g. metformin, statins, renin-angiotensin system inhibitors) may also have pleiotropic mechanisms. Newer strategies are investigating other lipid targets (especially HDL cholesterol) or using agents, such as thiazolidinediones, that address multiple established and emerging risk factors. A recent study with pioglitazone suggests that macrovascular risk can be reduced in very high-risk patients with type 2 diabetes who are already receiving contemporary lipid, anti-hypertensive, and anti-platelet therapy.

CONCLUSION

The core therapeutic paradigm targeting glycemia, hypertension, dyslipidemia, and coagulation factors has failed to remove excess residual risk in patients with type 2 diabetes completely. Emerging data, and on-going trials, should provide better guidance on new therapeutic opportunities in this high-risk patient group.

Differential Effects of β-Blockers on Albuminuria in Patients With Type 2 Diabetes

Increases in the cardiovascular risk marker microalbuminuria are attenuated by blood pressure reduction using blockers of the renin-angiotensin system. Such changes in microalbuminuria have not been observed when β-blockers are used. A prespecified secondary end point of the Glycemic Effects in Diabetes Mellitus Carvedilol-Metoprolol Comparison in Hypertensives (GEMINI) trial was to examine the effects of different β-blockers on changes in albuminuria in the presence of renin-angiotensin system blockade. Participants with hypertension and type 2 diabetes were randomized to either metoprolol tartrate (n=737) or carvedilol (n=498) in blinded fashion after a washout period of all antihypertensive agents except for angiotensin-converting enzyme inhibitors or angiotensin receptor blockers. Blinded medication was titrated to achieve target blood pressure, with a-5 month follow-up period. The current analysis examined microalbuminuria, using spot urine albumin:creatinine, in participants who had values at screening and trial end. A greater reduction in microalbuminuria was observed for those randomized to carvedilol (−16.2%Δ; 95% confidence interval, −25.3, −5.9; P =0.003). Of those with normoalbuminuria at baseline, fewer progressed to microalbuminuria on carvedilol versus metoprolol (20 of 302 [6.6%] versus 48 of 431 [11.1%], respectively; P =0.03). Microalbuminuria development was not related to differences in blood pressure or achievement of blood pressure goal (68% carvedilol versus 67%, metoprolol). Presence of metabolic syndrome at baseline was the only independent predictor of worsening albuminuria throughout the study ( P =0.004). β-Blockers have differential effects on microalbuminuria in the presence of renin-angiotensin system blockade. These differences cannot be explained by effects on blood pressure or α1-antagonism but may relate to antioxidant properties of carvedilol.

Kidney Disease and the Metabolic Syndrome

The epidemic of metabolic syndrome contributes to the rapid growth of cardiovascular and renal diseases. Hyper-hemodynamics, impaired pressure natriuresis, excess excretory load, insulin resistance, endothelial dysfunction, chronic inflammation, and prothrombotic status individually and interdependently initiate renal injury in metabolic syndrome. The prevention and treatment of kidney disease require a multifactorial approach. Weight loss through diet control and exercise can reverse many pathophysiologic processes. Pharmacologic intervention includes insulin sensitizers, tight glycemic and lipid control, blockage of renin angiotensin aldosterone system, and anti-inflammatory and antithrombotic therapies. Each peroxisome proliferator-activated receptor isoform plays a distinct role in metabolic syndrome, and their agonists may prevent or reverse the early renal injuries.

Losartan titration versus diuretic combination in type 2 diabetic patients

METHODS

We compared the effects of Losartan dose titration to 100 mg versus the addition of 12.5 mg of hydrochlorothiazide, in 90 type 2 diabetic patients with microalbuminuria and blood pressure > 130/85 mmHg, receiving losartan 50 mg as initial treatment during 4 weeks.

RESULTS

With the first dose of losartan, systolic (SBP) and diastolic blood pressure (DBP) decreased from 154.5 (152.1-157.5) to 144.4 (141.3-147.5) mmHg (P < 0.001) and from 91.1 (89.4-92.8) to 84.6 (82.8-86.4) mmHg (P < 0.001), with 20 patients attaining the expected goal blood pressure (< 130/85 mmHg); albuminuria decreased from 109.8 (90.5-133.3) to 83.5 (63.6-109.5) mg per 24 h (P = 0.006). Patients not attaining the target blood pressure were randomly allocated to titration or to the combination arm. After an additional 4 weeks, patients titrated exhibited a fall in SBP and DBP from 157.1 (152.7-161.5) to 142.1 (136.4-147.8) mmHg (P < 0.001) and from 92.4 (89.5-95.3) to 83.6 (81.1-86.1) mmHg (P < 0.001); albuminuria decreased from 136.3 (97.8-189.9) to 99.7 (69.3-143.4) mg per 24 h (P = 0.002). In the combination arm, there were similar reductions in SBP and DBP from 155.3 (151.5-159.1) to 139.1 (132.1-146.1) mmHg (P < 0.001) and from 92.1 (89.3-94.9) to 80.9 (77.4-84.4) mmHg (P < 0.001); while albuminuria fell from 107.7 (82.2-141.0) to 64.2 (45.9-89.9) mg per 24 h (P = 0.001).

CONCLUSIONS

Losartan 50 mg was effective in reducing blood pressure and albuminuria in type 2 diabetic patients. When the blood pressure target was not reached, the two strategies tested seem to contribute similarly to further reductions in blood pressure and albuminuria.

Genetic polymorphism of heparan sulfate proteoglycan (perlecan, HSPG2), lipid profiles and coronary artery disease in the Australian population

Perlecan is one of the three major classes of heparan sulfate proteoglycans (HSPGs) within the cardiovascular system; it interacts with lipid metabolism by binding to lipoprotein lipase (LpL) and apolipoprotein B (apo B) and may be related to vascular disease. We explored interactions between an HSPG2 polymorphism (BamHI marker), and apo B and coronary artery disease (CAD) in patients undergoing coronary angiography. The frequencies of the HSPG2 BamHI +/+, +/-, and -/- genotypes were 4.7, 31.7 and 63.6%, respectively, with a '+' allele frequency of 20.6%. The genotype distribution was in Hardy-Weinberg equilibrium (chi(2)=0.669, P0.05). The +/+homozygotes had the lowest apo B levels (0.74+/-0.06 g/l, n=36) compared to +/- (0.89+/-0.03 g/l, n=241) and -/- (0.93+/-0.02 g/l, n=480) genotypes. Although plasma apo B concentration was the strongest lipid risk factor for significant CAD, the HSPG2 genotypes were not independently associated with the presence of CAD (P=0.640 in males; P=0.224 in females), with significant CAD (P=0.764; P=0.110) or with the number of significantly stenosed coronary arteries (P=0.945; P=0. 335). In Australian Caucasians undergoing coronary angiography the HSPG2 BamHI polymorphism is associated with lower circulating apo B but not with the occurrence or severity of CAD. This may be due to HSPG2-mediated alterations in the HSPG2-apo B-LpL system and requires further exploration.