Insulin resistance in systemic hypertension: pharmacotherapeutic implications

Elevated resistin levels in chronic kidney disease are associated with decreased glomerular filtration rate and inflammation, but not with insulin resistance

In the present study, we explore the role of decreased renal function and a genetic polymorphism on the recently discovered protein resistin, apparently able to inhibit hepatic insulin action in mice. We also investigate possible links with inflammation and the insulin resistance present in patients with chronic kidney disease (CKD). This is a post hoc, cross-sectional study comparing 239 prevalent CKD patients with varying degrees of renal function impairment with an age- and gender-matched randomly selected control group of 25 individuals. Glomerular filtration rate (GFR) was estimated by the mean of urea and creatinine clearance (24-h urine samples) (n=204) or by iohexol clearance (n=60). Plasma analysis of blood lipids, insulin, glucose, inflammatory markers (high-sensitivity C-reactive protein, interleukin-6, tumor necrosis factor-alpha, vascular cellular adhesion molecule, intercellular adhesion molecule) and resistin (kit from LINCO Research, St Charles, MS) was performed using commercially available assays or routine methods. Insulin resistance was estimated by quantitative insulin-sensitivity check index (QUICKI) and homeostasis model assessment for insulin resistance (HOMA-IR) and body composition by dual-energy X-ray absorptiometry. Genotyping of a C/G promoter single nucleotide polymorphism (n=168) at position -180 of the resistin gene was performed by PyroSequencing. Serum levels of resistin were markedly elevated in the CKD patients with both advanced (39.9+/-1.3 ng/ml) and mild to moderate (23.2+/-1.0 ng/ml) renal function impairment, as compared to controls (8.5+/-0.7 ng/ml; P<0.001). In a multiple linear regression model in patients (adjusted r(2)=0.60), only GFR (beta=3.4; P<0.0001), lean body mass (beta=2.2; P<0.001) and the inflammatory markers were independently associated with circulating resistin levels. There was a weak but significant impact of -180 C/G genotype on plasma levels of resistin (median 43.0+/-2.4 ng/ml in CC, 37.5+/-2.0 ng/ml in CG, and 41.1+/-4.9 ng/ml in GG; P<0.05). Univariate analysis of non-diabetic patients and controls showed that serum resistin was associated with markers of glucose metabolism. However, in a multiple regression model, resistin, as well as all the measured markers of inflammation, was only associated with insulin resistance if GFR was not taken into account. Circulating resistin levels are strongly associated with both GFR and inflammatory biomarkers in CKD. As the significant relationship between plasma resistin levels and insulin resistance was lost following the correction for GFR, resistin is not a likely mediator of insulin resistance in patients with CKD. Renal function is an important factor to take into account in clinical studies relating insulin sensitivity to inflammatory biomarkers in CKD as well as in patients with diabetes mellitus, who often have an impaired renal function.

Diabetes mellitus and coronary artery disease: therapeutic considerations

Diabetes mellitus affects about 6% of the U.S. population and represents a significant public health challenge, with numbers of those affected increasing every year. The most common cause of death in these patients is macrovascular disease, with coronary disease being the predominant form. The pathophysiology of coronary disease in patients with diabetes is complex and involves elements of hyperglycemia, dyslipidemia, hyperinsulinemia, as well as a procoagulant vascular milieu. First-generation trials looking at revascularization of multivessel disease in patients with diabetes have had long clinical follow-up periods and seem to consistently favor coronary bypass grafting over percutaneous interventions; however, newer trials that include the use of stents and glycoprotein IIb/IIIa inhibitor therapy as part of the latter strategy have raised some interesting questions, so that the issue remains controversial and by no means settled.

The effect of fiber-rich carbohydrates on features of Syndrome X

There has been much debate among nutritionists and scientists regarding the optimal dietary approach for the treatment of the Insulin Resistance Syndrome, also called Syndrome X. This condition, which may affect as many as 47 million individuals in the United States, significantly increases risk of coronary heart disease and stroke. Major health organizations have historically recommended high-carbohydrate, low-fat (HCLF) diets to reduce chronic disease risk. However, there is evidence that a high intake of carbohydrates may adversely affect one or more of the abnormalities associated with this syndrome. Studies in this area have often had limitations. For example, some studies showing adverse effects of an HCLF diet have not taken into account the dietary fiber content of the diet. This article describes abnormalities often associated with Syndrome X, reviews the beneficial effects of fiber-rich carbohydrates, discusses the effect of fiber-rich carbohydrates on features of this syndrome, and concludes with applications of these findings for those involved in treating individuals with features of this disorder. This review indicates that an HCLF dietary pattern such as that used in the DASH trial, with a level of dietary fiber consistent with the recommendations of the American Dietetic Association (eg, 20-35g/day), containing from 3 to 10 g soluble fiber/day, may be beneficial for treating those with Syndrome X.

Biologic markers as predictors of cardiovascular disease

Epidemiologic data obtained over the past 30 years suggest that a number of new biologic markers are associated with increased risk for cardiovascular disease. These include indices related to (1) altered glucose metabolism, particularly insulin resistance; (2) hyperlipidemia; (3) elevated levels of lipoprotein(a) and homocysteine; (4) increased levels of molecules reflecting decreased fibrinolysis and increased activation of the coagulation cascade; (5) elevations in cell adhesion molecules and other markers of endothelial function; and (6) elevations in molecules associated with infection, inflammation, and vascular remodeling. Changes in molecules associated with increased risk usually occur in clusters. This clustering suggests that effective treatment of one marker may have positive effects on multiple markers. Indeed, several studies have demonstrated that therapies designed to reduce hyperlipidemia may also lower the plasma levels of factors associated with increased coagulation and reduced fibrinolysis. Thus, careful assessment of patient risk factors, and the development of therapies directed toward chains of markers associated with increased risk, may significantly alter the course of cardiovascular disease.

Insulin sensitivity in a long-term crossover trial with celiprolol and other antihypertensive agents

The effects of a vasodilating beta-blocker, celiprolol, on insulin sensitivity and cardiovascular risk factors were compared with those of another beta1-selective adrenoceptor blocker, calcium channel blockers, and angiotensin-converting enzyme (ACE) inhibitors. A randomized 21-month crossover trial was carried out with 25 patients with dyslipidemia receiving antihypertensive monotherapy. The study consisted of a 3-month active run-in period and two treatment periods, during which the patients received celiprolol (200-400 mg daily) or the control drug for 12 and 6 months in a crossover manner. A hyperinsulinemic euglycemic clamp and an oral glucose tolerance test (OGTT) were performed every 6 months. According to the clamp tests, the insulin-sensitivity index increased on average by 32% (p < 0.0001) during celiprolol treatment compared with that with the other antihypertensive agents, including ACE inhibitors. In OGTT, area under the incremental glucose curve decreased by 36% (p = 0.002) during celiprolol treatment, whereas insulin secretion diminished on average by 26% (p = 0.006). The mean decrease in fasting serum triglycerides was 11% (NS), whereas the high-density lipoprotein to low-density lipoprotein (HDL/LDL) ratio increased by 15% (p = 0.012). The results suggest that celiprolol improves insulin sensitivity of hypertensive patients with dyslipidemia in long-term therapy.

Moderately obese, insulin-resistant women exhibit abnormal vascular reactivity to stress

To define the hemodynamic implications of insulin resistance (IR), we compared 10 normotensive, insulin-resistant women who had abnormal glucose tolerance tests with 10 age-matched healthy normotensive women with normal glucose tolerance tests with respect to mental arithmetic and handgrip responses. Hemodynamic variables obtained at baseline and during stress included heart rate, blood pressure, cardiac output, and systemic vascular resistance. The IR group weighed more (84 versus 66 kg). Screening BP was similar (123/72 versus 120/68 mm Hg, P=NS) between groups although baseline diastolic BP at testing day was higher in the IR group than control group (75 versus 65 mm Hg, P<.05). The IR group showed a significantly greater increase in systolic (18% versus 10%, P<.O1) and diastolic (24% versus 12%, P<.01) blood pressure responses to mental stress than the control group. During mental stress, the control group demonstrated increased cardiac output (1.4 L/min) and decreased systemic vascular resistance (-120 dyne x s x cm[-5]), whereas IR subjects demonstrated increased systemic vascular resistance (119 dyne x s x cm(-5); group difference, P<.02) with only a small increase in cardiac output (0.5 L/min). Handgrip also caused a greater increase in systemic vascular resistance in the IR group (252 versus 64 dyne x s x cm(-5), P<.05), with a correspondingly greater increase in blood pressure than control subjects. Baseline blood pressure was correlated with weight (r=.41, P<.02) and stress blood pressure with fasting insulin (r=.51, P<.001) and glucose-to-insulin ratio (r= -.55, P<.001). We conclude that insulin resistance is associated with an exaggerated blood pressure response to stress; an enhanced vasoconstriction to stress may mediate this response. This hyperreactivity may be a marker for future hypertension in obese, normotensive, hyperinsulinemic individuals.

Lisinopril. A review of its pharmacology and use in the management of the complications of diabetes mellitus

Lisinopril, like other ACE inhibitors, lowers blood pressure and preserves renal function in hypertensive patients with non-insulin-dependent or insulin-dependent diabetes mellitus (NIDDM or IDDM) and early or overt nephropathy, without adversely affecting glycaemic control or lipid profiles. On available evidence, renoprotective effects appear to be greater with lisinopril than with comparator calcium channel blockers, diuretics and beta-blockers, despite similar antihypertensive efficacy. As shown by the EUCLID (EUrodiab Controlled trial of Lisinopril in Insulin-Dependent Diabetes) trial, lisinopril is also renoprotective in normotensive patients with IDDM and microalbuminuria. The effect in normotensive patients with normoalbuminuria was smaller than in those with microalbuminuria, and no conclusions can yet be made about its use in patients with normoalbuminuria. In complications other than nephropathy, lisinopril has shown some benefit. Progression to retinopathy was slowed during 2 years' lisinopril therapy in the EUCLID study. Although not yet fully published, these results provide the most convincing evidence to date for an effect of an ACE inhibitor in retinopathy. The drug may also improve neurological function, but this finding is preliminary. Lastly, post hoc analysis of the GISSI-3 trial indicates that lisinopril reduces 6-week mortality rates in diabetic patients when begun as early treatment after an acute myocardial infarction. The tolerability profile of lisinopril is typical of ACE inhibitors and appears to be similar in diabetic and nondiabetic individuals. Hypoglycaemia has occurred at a similar frequency with lisinopril and placebo, as shown in the EUCLID trial. In addition, the GISSI-3 study indicates that the incidence of persistent hypotension and renal dysfunction is increased with lisinopril in general, but the presence of diabetes does not appear to confer additional risk of these events in diabetic patients with acute myocardial infarction receiving lisinopril. In summary, lisinopril lowers blood pressure and produces a renoprotective effect in patients with IDDM and NIDDM without detriment to glycaemic control or lipid profiles. Like other ACE inhibitors, lisinopril should thus be viewed as a first-line agent for reducing blood pressure and preventing or attenuating nephropathy in hypertensive diabetic patients with IDDM or NIDDM and microalbuminuria or overt renal disease. The EUCLID study, using lisinopril, provides new data supporting an additional place in managing normotensive patients with microalbuminuria and IDDM. These findings, together with some evidence for an effect of lisinopril in delaying progression of retinopathy and in reducing mortality, suggest a broader role for the drug in managing diabetic vascular complications.