Is hypertension an insulin-resistant state? Metabolic changes associated with hypertension and antihypertensive therapy

Analyzing Blood Pressure Ascent during Aging in Non-Diabetics: Focusing on Links to Insulin Resistance and Body Fat Mass

BACKGROUND

A gradual upward progression of blood pressure (BP) occurs regularly in most humans during aging. This is unfortunate, because it is generally recognized that elevation of BP, even when relatively mild, is eventually detrimental to human health. Accordingly, considerably more understanding of the pathophysiology behind such a phenomenon is important in order to institute the correct remedies. Two components of the ubiquitous metabolic syndrome (MS) with nutritional implications, elevated insulin resistance (IR) and excess body fat mass (FM), are often postulated to be critical driving forces behind the elevated BP that is common with aging. The current study, therefore, focuses on the presence and importance of IR and/or body FM in BP regulation of non-diabetics over the lifespan.

METHODOLOGY

In cross sectional analyses, baseline data obtained from healthy, non-diabetic volunteers involved in prior clinical studies were analyzed by examining links between FBG measurements used as a surrogate for IR and body FM through their individual and combined effects on BP.

RESULTS

A significant positive correlation was found between FBG and FM and also between each employed individually as independent variables to the dependent BP and heart rate (HR) variables. In volunteers with higher body FM compared to lower, average systolic BP (SBP) values are increased to some extent at the same FBG measurement suggesting that other factors related to FM in addition to IR are the basis for slight pressure differences. Considering quartiles based upon levels of FM and FBG, low FM-low FBG display significantly reduced average SBP, diastolic blood pressure (DBP), and HR compared to the upper FM-FBG quartiles. While readings of FBG and FM display a decline in elderly subjects after age 70 years (aging paradox), such does not occur with SBP.

CONCLUSIONS

IR is a major driving force behind BP regulation even in non-diabetics. FM influences BP substantially through its relationship with IR and also via other mechanisms directly linked to FM.

Blood Pressure Regulation: Reviewing Evidence for Interplay Between Common Dietary Sugars and Table Salt

A popular concept is that the significant global progression in prevalence and intensification of elevated blood pressure (BP) levels is due in part to dietary indiscretions. Excess intake of several food sources causing overweight/obesity plays an important role in BP perturbations. However, certain nutrients are involved in ways other than via body fat accumulation, particularly table salt (sodium chloride) and popular refined carbohydrates like dietary sugars (sucrose, fructose, high fructose corn syrup). In nondiabetics and diabetics, several functions of salt and sugar influence BP and metabolism. For example, salt intake is linked to volume expansion, insulin resistance, and hypertension, while sugar intake is associated with enhanced salt sensitivity via urinary sodium retention, insulin resistance, and hypertension. The key postulate evaluated here is that when two popular nutrients-salt and dietary sugars-are consumed together in adequate amounts, their respective individual BP effects are significantly amplified. In previous laboratory studies, a sugar challenge did not increase BP in the face of marked sodium depletion, and combining sugar and salt challenges caused a synergistic BP elevation. Among examples of amplification on the clinical side, the greatest increases in BP following sugar challenges were seen in diabetic subjects having the highest sodium excretion. Interplay between table salt and common dietary sugars in BP regulation is a reasonable postulate and should be carefully considered when developing optimal prevention and treatment regimens to ameliorate the worldwide crisis arising from harmful elevated BP levels.

Fiber, protein, and lupin-enriched foods: role for improving cardiovascular health

Cardiovascular diseases (CVD) are the leading cause of death globally (World Health Organisation, 2011). Many of the risk factors for CVD are modifiable, including overweight and obesity. Numerous strategies have been proposed to fight CVD, with a special focus being placed on dietary interventions for weight management. The literature suggests that two nutrients, fiber and protein, may play significant roles in weight control and hence cardiovascular health. Increasing both protein and fiber in the diet can be difficult because popular low-carbohydrate and high-protein diets tend to have considerably low-fiber intakes (Slavin, 2005). One approach to obtain both is to develop functional foods using unique ingredients. Lupin flour is a novel food ingredient derived from the endosperm of lupin. It contains 40-45% protein, 25-30% fiber, and negligible sugar and starch (Petterson and Crosbie, 1990). Research conducted to date reveals that lupin-enriched foods, which are naturally high in protein and fiber, may have a significant effect on CVD risk factors. This review explores whether there is a role for fiber-, protein-, and lupin-enriched foods in improving cardiovascular health.

Angiotensin‐converting enzyme 2 as a novel target for gene therapy for hypertension

Less than one-third of patients with hypertension have their blood pressures (BP) controlled with current traditional therapeutic approaches for the treatment and control of hypertension. Pharmacological approaches may have reached a plateau in their effectiveness and thus newer innovative strategies need to be studied not only to increase the number of patients that can achieve BP control, but also to find a way to cure, not just manage, the disease. Continuous advances in gene delivery systems coupled with the completion of the Human Genome Project, now make it possible to investigate genetic means for the treatment and possible cure for hypertension. The renin-angiotensin system (RAS) has long been known to regulate BP, and salt and water metabolism. This system is unique in having both a peripheral circulating system and a tissue-based system. Each of these components have been ascribed a variety of physiological effects that have been associated with not only an increase in BP, but also in a variety of the pathophysiological manifestations associated with hypertension, such as cardiac hypertrophy and kidney dysfunction. We and others have used an antisense gene therapy approach, targeting the classical components of the RAS, to effectively attenuate the development of hypertension and related cardiovascular pathophysiologies in numerous experimental models of hypertension. Recently other components of the RAS have been elucidated and some of these components may be potential targets in a gene therapy approach. This article will focus on angiotensin-converting enzyme 2 (ACE2) as a new, potential target of gene therapy for hypertensive disorders.

Increase in blood glucose concentration during antihypertensive treatment as a predictor of myocardial infarction: population based cohort study

OBJECTIVE

To investigate the impact of an increase in blood glucose on the risk of developing myocardial infarction, with particular emphasis on people taking antihypertensive drugs.

DESIGN

Prospective population based cohort study.

SETTING

Uppsala, Sweden.

PARTICIPANTS

1860 men who had participated in 1970-3 at age 50 in a health survey aimed at identifying risk factors for cardiovascular disease and were re-examined at age 60 and then followed for 17.4 years. MIN OUTCOME MEASURE: Myocardial infarction after age 60.

RESULTS

The incidence of myocardial infarction was significantly higher in men treated for hypertension than in those without such treatment (23% v 13.5%, P<0.0001). Participants who developed myocardial infarction after the age of 60 (n=253) showed a significantly larger increase in blood glucose between age 50 and 60 than did those without myocardial infarction. In multivariate Cox proportional hazard models increase in blood glucose was an independent risk factor for myocardial infarction (P=0.0001) in men receiving antihypertensive treatment at age 60 (n=291, mainly beta blockers and thiazide diuretics) but not in those without such treatment. The impact of increase in blood glucose declined after inclusion of serum proinsulin concentrations at baseline but was still significant. A significant interaction existed between proinsulin concentration (a marker of insulin resistance) at baseline and antihypertensive treatment on increase in blood glucose.

CONCLUSIONS

Increase in blood glucose between the ages of 50 and 60 and baseline proinsulin concentration were important risk factors for myocardial infarction in men receiving antihypertensive treatment, indicating that both an insulin resistant state and the metabolic impact of beta blockers and diuretics increase the risk of myocardial infarction.

Effects of a water-soluble extract of maitake mushroom on circulating glucose/insulin concentrations in KK mice

AIM

We examined benefits of a water-soluble extract of maitake mushroom designated as Fraction X (FXM) on the glucose/insulin metabolism of insulin-resistant KK mice, and compared the results of FXM with those of a sulphonylurea, Glipizide.

DESIGN

In several acute studies, insulin-resistant KK mice were gavaged with a single dose of varying concentrations of FXM, or a single dose of one concentration of the oral hypoglycaemic drug, Glipizide. In the one chronic study, KK mice were gavaged with FXM, Glipizide, or an equal volume of isotonic saline (baseline control) twice daily. Retro-orbital blood was drawn on the morning of the 4th and 7th days before the early gavage. Blood glucose was measured by routine laboratory procedures, and serum insulin was estimated by a radioimmunoassay (RIA) assay developed specifically for rodents.

RESULTS

At a dose of FXM (140 mg/mouse), a statistically significant lowering of circulating glucose concentrations was again seen at 8-12 h and 16-18 h after oral gavage. The lowering approximated 25% of the original concentration. Oral gavage of Glipizide resulted in statistically significantly lower values of circulating glucose (25-37% lower compared with baseline) at 8-24 h post dosing. In the chronic study, the circulating concentrations of glucose and insulin of mice taking 140 mg FXM per day were decreased significantly at days 4 and 7.

CONCLUSIONS

FXM, a natural extract obtained from maitake mushroom, favourably influences glucose/insulin metabolism in insulin-resistant KK mice. The lowering of both circulating glucose and insulin concentrations suggests that FXM works primarily by enhancing peripheral insulin sensitivity.

Insulin induces upregulation of vascular AT1 receptor gene expression by posttranscriptional mechanisms

BACKGROUND

An interaction of insulin with angiotensin II effects could be pathophysiologically important for the pathogenesis of atherosclerosis and hypertension.

METHODS AND RESULTS

We examined the effect of insulin on AT1 receptor gene expression in cultured vascular smooth muscle cells (VSMCs). A 24-hour incubation with insulin (100 nmol/L) produced a 2-fold increase in AT1 receptor density on VSMCs, as assessed by radioligand binding assays. This enhanced AT1 receptor expression was caused by a time- and concentration-dependent upregulation of the AT1 receptor mRNA levels, as assessed by Northern analysis. The maximal effect was detected after a 24-hour incubation of cells with 100 nmol/L insulin (270+/-20%). AT1 receptor upregulation was caused by a stabilization of the AT1 receptor mRNA, because the AT1 receptor mRNA half-life was prolonged from 5 hours under basal conditions to 10 hours after insulin stimulation. In contrast, insulin had no influence on AT1 receptor gene transcription, as assessed by nuclear run-on assays. The insulin-induced AT1 receptor upregulation was followed by an increased functional response, because angiotensin II evoked a significantly elevated intracellular release of calcium in cells that were preincubated with 100 nmol/L insulin for 24 hours. The insulin-induced AT1 receptor upregulation was dependent on tyrosine kinases, as assessed by experiments with the tyrosine kinase inhibitor genistein. Furthermore, experiments using the intracellular calcium chelator bis(2-amino-5-methylphenoxy)ethane-N, N,N',N'-tetraacetic acid tetraacetoxymethyl ester suggest that intracellular calcium release may be involved in AT1 receptor regulation.

CONCLUSIONS

Insulin-induced upregulation of the AT1 receptor by posttranscriptional mechanisms may explain the association of hyperinsulinemia with hypertension and arteriosclerosis, because activation of the AT1 receptor plays a key role in the regulation of blood pressure and fluid homeostasis.

Sugar-induced blood pressure elevations over the lifespan of three substrains of Wistar rats

OBJECTIVE

Since the majority of studies concerned with sugar-induced blood pressure elevation have principally been short-term, the present investigation followed the effects of heavy sucrose ingestion on systolic blood pressure (SBP) and related parameters over the lifespan of three substrains of Wistar rats.

METHODS

Two hundred twenty-five rats (75 spontaneously hypertensive rats (SHR), 75 Wistar Kyoto rats (WKY), 75 Munich Wistar rats (WAM) were given one of five diets. The baseline diet in terms of calories derived 32% from sucrose, 33% from protein, and 35% from fat. The remaining four diets derived their calories as follows: a high sugar-low protein diet--52% of calories from sucrose, 15% from protein, and 33% from fat; a high sugar-low fat diet--53% of calories from sucrose, 37% from protein, and 10% from fat; a low sugar-high protein diet--11% calories from sucrose, 56% from protein, and 33% from fat, and a low sugar-high fat--13% of calories from sucrose, 32% from protein, and 55% from fat.

RESULTS

All substrains showed the highest systolic blood pressure when ingesting the two diets highest in sucrose. The highest sugar-induced SBP elevation, which remained over the lifespan of all substrains, was found in SHR. WKY had an intermediate elevation. WAM showed the lowest responses, although the average elevation of 6-8 mm Hg was statistically significant. The following parameters could not be correlated with long-term elevation of SBP; body weight, catecholamine excretion, renal function, and plasma renin activity. Only insulin concentrations correlated: insulin concentrations were consistently higher in the two groups of WKY and WAM consuming the high sucrose diets.

CONCLUSIONS

High dietary sucrose can chronically increase SBP in three substrains of Wistar rats. Increased concentrations of circulating insulin were found in WKY and WAM suggesting that the glucose/insulin system was involved, at least in these two substrains, in the maintenance of high SBP levels during chronic, heavy sugar ingestion.

Effects of glucose/insulin perturbations on aging and chronic disorders of aging: the evidence

Among changes associated with aging is a decline in glucose tolerance. The reported causes are increased insulin resistance from receptor and/or post receptor disturbances and diminished pancreatic islet B-cell sensitivity to glucose. Many recent reports indicate that insulin resistance with hyperinsulinemia and/or hyperglycemia contribute to or even causes many chronic disorders associated with aging, i.e., chronic metabolic perturbations including noninsulin-dependent diabetes mellitus, obesity, hypertension, lipid abnormalities, and atherosclerosis. How could such disturbances in glucose/insulin metabolism lead to many chronic disorders associated with aging? In aging, similar to diabetes, the elevation in circulating glucose and other reducing sugars secondary to age-induced insulin resistance can react nonenzymatically with proteins and nucleic acids to form products that affect function and diminish tissue elasticity. Also, perturbations in glucose/insulin metabolism are associated with enhanced lipid peroxidation secondary to greater free radical formation. Free radicals of oxygen are important known causes of tissue damage and have been associated with many aspects of aging including inflammatory diseases, cataracts, diabetes, and cardiovascular diseases. Augmented free radical formation and lipid peroxidation are not uncommon in diabetes mellitus, commonly associated with "premature aging". Ingestion of sugars, fats, and sodium have been linked to decreased insulin sensitivity, while caloric restriction, exercise, ingestion of chromium, vanadium, soluble fibers, magnesium, and certain antioxidants are associated with greater insulin sensitivity. Thus, manipulation of diet by influencing the glucose/insulin system may favorably affect lifespan and reduce the incidence of chronic disorders associated with aging.

Effects of calcium antagonists on insulin sensitivity and other metabolic parameters

The antihypertensive efficacy of calcium antagonists appears to be comparable to that of oral diuretics when used as monotherapy. Peripheral vascular dilation appears to be the principal mechanism of the long-term blood pressure-lowering effects of calcium antagonists. The calcium antagonists appear to have beneficial effects with respect to maintenance of renal blood flow and glomerular filtration rate. Metabolic abnormalities associated with diuretic and beta-blocker antihypertensive therapy, such as hypokalemia, hypercalcemia, hyperuricemia, lipid changes, and hyperglycemia, are generally not observed with calcium antagonists.

Calcium channel blockers and hypertension: evolving perspective--1996

In recent years, calcium channel blockers (CCBs) have been used extensively in the United States and elsewhere as antihypertensive agents, and their availability has been an important advance in the management of hypertension. As antihypertensive agents, the CCBs thus appear considerably more versatile than most previous vasodilators. The available studies indicate that CCBs are metabolically neutral and do not exacerbate dyslipidemia or impair glucose tolerance. In contrast to diuretics and beta-blockers, CCBs do not appear to alter insulin sensitivity. The CCBs also differ from previous vasodilators because of their favorable accompanying effects on the heart and kidney. Despite the attributes of CCBs enumerated earlier, a number of recent retrospective analyses by Psaty et al. (JAMA 1995;274:620-625) have suggested that CCBs may be detrimental and may promote adverse cardiovascular events. I have recently reviewed the results of Psaty's meta-analysis and report (Arch Intern Med 1995;155: 2150-2156). I have emphasized that it is the rate of drug delivery into the systemic circulation that produces profound effects on the hemodynamic and neurohumoral responses to a dihydropyridine CCB drug. During chronic treatment with dihydropyridines, major fluctuations in blood pressure (rapid onset and offset of antihypertensive effects) during the dosing interval may persist for drugs and formulations that are short acting. In contrast, slow-release formulations of otherwise rapidly absorbed dihydropyridines achieve a more gradual and sustained antihypertensive effect. It is probable that newer CCB formulations that do not provoke intermittent sympathetic activation and do not evoke a cardioacceleratory response would not be expected to promote adverse cardiovascular events.

Diabetes mellitus and raised serum triglyceride concentration in treated hypertension--are they of prognostic importance? Observational study

OBJECTIVE

To analyse whether metabolic changes during long term treatment with antihypertensive drugs are associated with an increased risk of coronary heart disease.

DESIGN

Observational study.

SETTING

Gothenburg, Sweden.

SUBJECTS

686 middle aged hypertensive men, recruited after screening of a random population sample, and followed for 15 years during treatment with predominantly beta adrenoceptor blockers or thiazide diuretics, or both. Coronary heart disease and diabetes mellitus were registered at yearly patient examinations. Entry characteristics, as well as within study serum concentrations of cholesterol and triglycerides and the development of diabetes mellitus, were related to the incidence of coronary heart disease in a time dependent Cox's regression analysis.

MAIN OUTCOME VARIABLE

Coronary heart disease morbidity.

RESULTS

Diabetes mellitus, raised serum cholesterol and triglyceride concentrations present at the beginning of the study were all significantly predictive of coronary heart disease in univariate analysis. The relative risk of diabetes mellitus and of a 1 mmol/l increase in the cholesterol and triglyceride concentrations was 2.12 (95% confidence interval 1.11 to 4.07), 1.21 (1.05 to 1.39), and 1.21 (1.03 to 1.43) respectively. However, when the within study metabolic variables were analysed, only the serum cholesterol concentration was significantly and independently associated with coronary heart disease (relative risk 1.07 (1.02 to 1.13)). Although the triglyceride concentrations increased slightly during the follow up, the within study serum triglyceride concentrations were not associated with the incidence of coronary heart disease (1.04 (0.96 to 1.10)). New diabetes mellitus-that is, onset during follow up-was not significantly associated with an increased risk for coronary heart disease (1.48 (0.37 to 6.00)).

CONCLUSIONS

Metabolic disturbances such as diabetes mellitus and hyperlipidaemia presenting before the start of antihypertensive treatment have a prognostic impact in middle aged, treated hypertensive men. Moreover, while within study cholesterol concentration was an independent predictor of coronary heart disease, drug related diabetes mellitus and raised serum triglyceride concentrations that are associated with treatment do not seem to have any major impact on the coronary heart disease prognosis in this category of patients.

Vascular insulin abnormalities, hypertension, and accelerated atherosclerosis

There is accumulating evidence that insulin resistance, glucose intolerance, and hyperinsulinemia exist in people with high blood pressure, and it has been suggested that insulin resistance and hyperinsulinemia may be of great importance in the origin of hypertension and its ultimate clinical course. Of importance are the recent observations that persons with normal glucose tolerance, selected on the basis of hyperinsulinemia, had higher blood pressure than matched individuals with normoinsulinemia. Hypertension in in insulin-resistant states generally has been attributed to hyperinsulinemia, with resulting increases in sympathetic nervous system activity. However, recent data from our laboratory suggest that cellular insulin resistance rather than hyperinsulinemia per se may lead to hypertension. The basic tenet proposed in this article is that a deficiency of insulin at the cellular level represents a common mechanism that is involved in the development of hypertension in both type I and type II diabetes mellitus. Insulin has an important role in the modulation of cellular calcium metabolism. Decreased insulin action on vascular smooth muscle cells may contribute both to hypertension and to accelerated atherosclerosis. Recent observations suggest that an impaired cellular response to insulin predisposes to increased vascular smooth muscle tone (the hallmark of hypertension in the diabetic state). For example, recently reported studies from our laboratory demonstrate that insulin attenuates the vascular contractile response to phenylephrine, serotonin, and potassium chloride. Thus, it appears that insulin normally modulates (attenuates) vascular smooth muscle contractile responses to vasoactive factors, and insulin resistance should accordingly be associated with enhanced vascular reactivity.