Vascular signaling pathways in the metabolic syndrome

Risk factors and fetal outcomes for preeclampsia in a Colombian cohort

In Latin America and the Caribbean, hypertensive pregnancy disorders are responsible for almost 26% of all maternal deaths [1] and, in Colombia, they account for 59% of all severe maternal morbidity (SMM) cases, and 59.7% of all SMM cases in adolescents [2]. One of the most important hypertensive pregnancy disorders is preeclampsia (PE). Lives can be saved, if PE is prevented, or detected early and properly managed. Prevention and detection depend on identifying the risk factors associated with PE, and, as these have been shown vary by population, they should be determined on a population-by-population basis. The following study utilized the nested case-control model to evaluate 45 potential PE risk factors of a cohort in Bogotá, Colombia, making it perhaps the most comprehensive study of its kind in Colombia. It found PE to have a statistically significant association with 7 of the 45 factors evaluated: 1) pre-gestational BMI >30 kg/m², 2) pregnancy weight gain >12 kg, 3) previous history preeclampsia/eclampsia, 4) previous history of IUGR-SGA (Intrauterine Growth Restriction-Small for Gestational Age), 5) maternal age <20 or ≥35 years (20–34 was not associated), and 6) family history of diabetes. Finally, prenatal consumption of folic acid was found to lower the risk of PE. We recommend that, in Colombia, factors 1–6 be used to identify at risk mothers during pregnancy check-ups; that mothers be encouraged to take folic acid during pregnancy; and, that Colombia's health system and public policy address the problem of pregestational obesity.

Adiponectin and hypertension

Adipose tissue secretes a variety of bioactive molecules, also known as adipocytokines or adipokines. Obesity, in particular, visceral fat accumulation, is implicated in the dysregulated secretion of adipocytokines, which can contribute to the development of metabolic syndrome and cardiovascular diseases. Adiponectin is an adipocytokine that is exclusively secreted from adipose tissue, but its plasma levels are reduced in obese subjects, especially those with visceral fat accumulation. Adiponectin has a variety of protective properties against obesity-linked complications, such as hypertension, metabolic dysfunction, atherosclerosis, and ischemic heart disease. Adiponectin exerts the beneficial effects on vascular disorders by directly affecting components of vascular tissue. This review will discuss clinical and experimental findings that examine the role of adiponectin in regulation of hypertension and vascular function.

Lipid peroxidation in relation to ageing and the role of endogenous aldehydes in diabetes and other age-related diseases

Lipid intermediates which are generated by ROS have drawn more attention after it was found that lipid peroxidation and lipid-radical cycles are two alternative processes. In biological membranes alpha-tocopherol and cytochrome b5, as known, act synergistically to overcome free radical injury and to form lipid-radical cycles. These cycles activate membrane proteins, protect membrane lipids from oxidation and prevent from formation of endogenous aldehydes. Experimental and clinical evidence accumulated for 5-6 years suggests that endogenous aldehydes, such as malonic dialdehyde (MDA) and methylglyoxal (MG), are the major initiators of the metabolic disorders. The age-related diseases emerge when cells cannot control formation of aldehydes and/or cannot abolish the negative effect of methylglyoxal on their metabolism. If the efficiency of the glyoxalase system is insufficient toxic aldehydes cause cumulative damage over a lifetime. In this paper, we provide evidence to consider ageing as a process in which lipid-radical cycles gradually substitute for lipid peroxidation. There are always two opposing tendencies or actions which counteract each other - actions of melatonin, lipid-radical cycles and the glyoxalase system (anti-ageing effect) and negative actions of the toxic aldehydes (pro-ageing effect). Life span is determined by the balance of two opposing processes.

Aldehydes and disturbance of carbohydrate metabolism: some consequences and possible approaches to its normalization

There are many well-documented errors of metabolism involving genetic defects that affect carbohydrate utilization. The array of disorders includes the defective utilization of glucose, as well as enzymatic deficiencies in glycolysis and gluconeogenesis, and the pentose phosphate pathway. Besides, there is considerable literature about metabolic syndrome and diabetes. However, the main problem of their origin remains obscure. Also, it is presently beyond doubt that there are various causes of insulin resistance. The development of insulin resistance may be associated not only with insulin production disorders or presence of insulin antagonists but also with modification of the number of receptors and sensitivity of peripheral tissues. The insulin resistance originates from insulin signal transmission defects at its initial stages. It is presently uncertain which mechanisms of adaptation regulation are activated or should be activated under hyperglycemia conditions. This is the main problem of the selection of strategy of hyperglycemia treatment but it is important that aldehydes - the secondary products of lipid peroxidation and protein glycation (malondialdehyde and methylglyoxal) - make a contribution to abnormal metabolism. As far as the role of methylglyoxal in inhibition of antioxidant enzymes is concerned, the involvement of the ketoaldehyde in such processes as oxidative stress, cell proliferation control, and carbohydrate metabolism disorders does not cast any doubt.

The atherogenic potential of dietary carbohydrate

OBJECTIVE

To investigate the role of dietary carbohydrate in atherogenesis.

METHOD

Search of the literature for relevant papers concerning the relationship of insulin/hyperinsulinemia and carbohydrate on the one hand, and the renin-angiotensin system, the sympathetic nervous system, growth factors, i.e. platelet-derived growth factor and insulin-like growth factor-I, C-reactive protein, and dyslipemia, on the other hand, factors well known to be involved in the atherogenic process, as well as for epidemiologic studies investigating the relationship between high-carbohydrate diets and the development of cardiovascular disease.

RESULTS

High-carbohydrate nutrition is shown to have the ability to induce vascular inflammation and plaque formation through an insulin-mediated activation of the RAS, growth factors, cytokines, the SNS, and C-reactive protein and to cause an atherogenic lipid profile in normal humans. Epidemiologic studies as well as studies in experimental animals corroborate an important role of dietary carbohydrate in atherogenesis.

CONCLUSION

High-carbohydrate diets, particularly in the form of high-glycemic index carbohydrate, have the ability to directly induce atherosclerosis. Based on anthropologic facts, the reason for these dietary-induced, insulin-mediated, atherogenic metabolic perturbations are suggested to be an insufficient adaptation to starch and sugars during human evolution. Restriction of insulinogenic food (starch and sugars) may help to prevent the development of atherosclerosis, one of the most common and costliest human diseases.

Temporal profiling of the transcriptional basis for the development of corticosteroid-induced insulin resistance in rat muscle

Elevated systemic levels of glucocorticoids are causally related to peripheral insulin resistance. The pharmacological use of synthetic glucocorticoids (corticosteroids) often results in insulin resistance/type II diabetes. Skeletal muscle is responsible for close to 80% of the insulin-induced systemic disposal of glucose and is a major target for glucocorticoid-induced insulin resistance. We used Affymetrix gene chips to profile the dynamic changes in mRNA expression in rat skeletal muscle in response to a single bolus dose of the synthetic glucocorticoid methyl-prednisolone. Temporal expression profiles (analyzed on individual chips) were obtained from tissues of 48 drug-treated animals encompassing 16 time points over 72 h following drug administration along with four vehicle-treated controls. Data mining identified 653 regulated probe sets out of 8799 present on the chip. Of these 653 probe sets we identified 29, which represented 22 gene transcripts, that were associated with the development of insulin resistance. These 29 probe sets were regulated in three fundamental temporal patterns. 16 probe sets coding for 12 different genes had a profile of enhanced expression. 10 probe sets coding for eight different genes showed decreased expression and three probe sets coding for two genes showed biphasic temporal signatures. These transcripts were grouped into four general functional categories: signal transduction, transcription regulation, carbohydrate/fat metabolism, and regulation of blood flow to the muscle. The results demonstrate the polygenic nature of transcriptional changes associated with insulin resistance that can provide a temporal scaffolding for translational and post-translational data as they become available.

Coenzyme Q10 and diabetic endotheliopathy: oxidative stress and the 'recoupling hypothesis'

Increased oxidative stress in diabetes mellitus may underlie the development of endothelial cell dysfunction by decreasing the availability of nitric oxide (NO) as well as by activating pro-inflammatory pathways. In the arterial wall, redox imbalance and oxidation of tetrahydrobiopterin (BH4) uncouples endothelial nitric oxide synthase (eNOS). This results in decreased production and increased consumption of NO, and generation of free radicals, such as superoxide and peroxynitrite. In the mitochondria, increased redox potential uncouples oxidative phosphorylation, resulting in inhibition of electron transport and increased transfer of electrons to molecular oxygen to form superoxide and other oxidant radicals. Coenzyme Q10 (CoQ), a potent antioxidant and a critical intermediate of the electron transport chain, may improve endothelial dysfunction by 'recoupling' eNOS and mitochondrial oxidative phosphorylation. CoQ supplementation may also act synergistically with anti-atherogenic agents, such as fibrates and statins, to improve endotheliopathy in diabetes.

Angiotensin II type-1 receptor blocker valsartan enhances insulin sensitivity in skeletal muscles of diabetic mice

Angiotensin II has been shown to contribute to the pathogenesis of insulin resistance; however, the mechanism is not well understood. The present study was undertaken to investigate the potential effect of an angiotensin II type-1 (AT1) receptor blocker, valsartan, to improve insulin resistance and to explore the signaling basis of cross-talk of the AT1 receptor- and insulin-mediated signaling in type 2 diabetic KK-Ay mice. Treatment of KK-Ay mice with valsartan at a dose of 1 mg/kg per day, which did not influence systolic blood pressure, significantly increased insulin-mediated 2-[3H]deoxy-d-glucose (2-[3H]DG) uptake into skeletal muscle and attenuated the increase in plasma glucose concentration after a glucose load and plasma concentrations of glucose and insulin. In contrast, insulin-mediated 2-[3H]DG uptake into skeletal muscle was not influenced in AT2 receptor null mice, and an AT2 receptor blocker, PD123319, did not affect 2-[3H]DG uptake and superoxide production in skeletal muscle of KK-Ay mice. Moreover, we observed that valsartan treatment exaggerated the insulin-induced phosphorylation of IRS-1, the association of IRS-1 with the p85 regulatory subunit of phosphoinositide 3 kinase (PI 3-K), PI 3-K activity, and translocation of GLUT4 to the plasma membrane. It also reduced tumor necrosis factor-alpha (TNF-alpha) expression and superoxide production in skeletal muscle of KK-Ay mice. Specific AT1 receptor blockade increases insulin sensitivity and glucose uptake in skeletal muscle of KK-Ay mice via stimulating the insulin signaling cascade and consequent enhancement of GLUT4 translocation to the plasma membrane.

Insulin-mediated regulation of the endothelial renin???angiotensin system and vascular cell growth

OBJECTIVE

Insulin has a growth-stimulating effect for vascular tissue. At the tissue level, the vascular renin-angiotensin system (RAS) may be involved in the progression of atherosclerosis or vascular hypertrophy. We previously reported that the vascular RAS activity is activated in vascular smooth muscle cells (SMC) by insulin stimulation. However, the effect of insulin on the RAS in endothelial cells (EC) is not fully understood.

METHODS

Cultured human EC were incubated with or without insulin. After incubation for 48 h, cellular angiotensinogen and renin mRNA expression and levels in the cells were quantified by slot-blot hybridization and radioimmunoassay. Angiotensin I converting enzyme (ACE) activity in EC homogenates was measured by modified Cushman and Cheung method. EC growth and SMC with or without EC using co-culture were assessed by 3H-thymidine uptake for evaluation of their growth.

RESULTS

All doses of insulin (10, 100, 1000 microU/ml) decreased angiotensinogen and renin mRNA expression (angiotensinogen: 19.3%, P < 0.05; 25.4%, P < 0.01; 26.2%, P < 0.01, renin: 12.9%, P < 0.05; 21.3%, P < 0.01; 14.3%, P < 0.05, respectively). Both cellular angiotensinogen and renin level were also reduced by high levels of insulin. Neither 10 nor 100 microU/ml insulin increased cellular angiotensin converting enzyme (ACE) activity (2.17 to 3.48-folds, P = 0.077, 0.125, respectively) significantly, but 1000 microU/ml insulin strongly up-regulated ACE activity by 16.67-folds (P = 0.001) in cultured EC. For the co-culture with EC and SMC, 100 microU/ml insulin was not able to induce SMC but 1000 microU/ml insulin accelerated SMC growth in the co-culture. In contrast insulin that was over 100 microU/ml induced SMC growth in the sole culture of SMC.

CONCLUSION

Either low or high levels of insulin suppressed angiotensinogen and renin expression, however, high doses of insulin stimulated ACE activity in cultured human aortic EC. This may indicate that insulin regulates vascular cell growth and endothelial function via bifunctional modification of the vascular angiotensin generation.

Family history of hypertension and type 2 diabetes in relation to preeclampsia risk

In a case-control study of 190 preeclamptic patients and 373 control subjects, we assessed maternal family history of chronic hypertension and type 2 diabetes in relation to preeclampsia risk. Participants provided information on first-degree family history of the 2 conditions and other covariates during postpartum interviews. Logistic regression was used to estimate odds ratios and 95% confidence intervals adjusted for confounding by age, race, and obesity. Compared with women with no parental history of hypertension, women with maternal only (odds ratio=1.9), paternal only (odds ratio=1.8), or both maternal and paternal history of hypertension (odds ratio=2.6) had a statistically significant increased risk of preeclampsia. The odds ratio for women with at least one hypertensive parent and a hypertensive sibling was 4.7 (95% confidence interval, 1.9 to 11.6). Both maternal only (odds ratio=2.1; 95% confidence interval, 0.9 to 4.6) and paternal only (odds ratio=1.9; 95% confidence interval, 1.0 to 3.2) history of diabetes was associated with an increased risk of preeclampsia. Women with a diabetic sibling had a 4.7-fold increased risk of preeclampsia (95% confidence interval, 1.1 to 19.8). For women with at least one hypertensive parent and at least one diabetic parent, relative to those with parents with neither diagnosis, the odds ratio for preeclampsia was 3.2 (95% confidence interval, 1.6 to 6.2). Our results are consistent with the thesis that family history of hypertension and diabetes reflects genetic and behavioral factors whereby women may be predisposed to an increased preeclampsia risk.

Can coenzyme Q10 improve vascular function and blood pressure? Potential for effective therapeutic reduction in vascular oxidative stress

Coenzyme Q10 (CoQ) is an endogenously synthesised compound that acts as an electron carrier in the mitochondrial electron transport chain. The presence of adequate tissue concentrations of CoQ may be important in limiting oxidative and nitrosative damage in vivo. Oxidative and nitrosative stress are likely to be elevated in conditions such as diabetes and hypertension. In these conditions elevated oxidative and nitrosative stress within the arterial wall may contribute to increased blood pressure and vascular dysfunction. The major focus of this review is the potential of CoQ to improve vascular function and lower blood pressure. Although there is substantial indirect support for the putative mechanism of effect of CoQ on the vascular system, to date there is little direct support for an effect of CoQ on in vivo markers of oxidative or nitrosative stress. The limited data available from studies in animal models and from human intervention studies are generally consistent with a benefit of CoQ on vascular function and blood pressure. The observed effects of CoQ on these endpoints are potentially important therapeutically. However, before any firm clinical recommendations can be made about CoQ supplementation, further intervention studies in humans are needed to investigate the effects of CoQ on vascular function, blood pressure and cardiovascular outcomes. The particularly relevant groups of patients for these studies are those with insulin resistance, type 2 diabetes, hypertension and the metabolic syndrome.

Mechanisms linking angiotensin II and atherogenesis

PURPOSE OF REVIEW

The concept that angiotensin II plays a central role in early atherogenesis, progression to atherosclerotic plaque, and the most serious clinical sequelae of coronary artery disease is the subject of considerable current interest. Results from recent large clinical trials confirm that blunting of the renin-angiotensin system through either angiotensin converting enzyme inhibition or angiotensin II type 1 receptor blockade incurs significant beneficial outcomes in patients with coronary artery disease. The exact mechanisms for these effects are not yet clear, but are suggested by studies demonstrating that suppression of the renin-angiotensin system is associated with muted vascular oxidative stress.

RECENT FINDINGS

As most of the biological effects of the renin-angiotensin system occur through stimulation of the angiotensin II type 1 receptor, the focus of this review is on changes in the vascular wall mediated by this receptor and primarily related to endothelial and vascular smooth muscle cells, monocyte/macrophages and platelets. The interactions between angiotensin II and nitric oxide exert particular demands on the vascular capacity to adapt to dyslipidemia, hypertension, estrogen deficiency and diabetes mellitus that appear to exacerbate atherogenesis. Associated with each of these conditions is angiotensin II-mediated stimulation of macrophages, platelet aggregation, plasminogen activator inhibitor 1, endothelial dysfunction, vascular smooth muscle cell proliferation and migration, apoptosis, leukocyte recruitment, fibrogenesis and thrombosis.

SUMMARY

Inhibition of the actions of angiotensin II serves a dual purpose: indirectly through reduction of mechanical stress on the vascular wall, and directly by diminished stimulation for vascular restructuring and remodeling. Collectively, data from studies published over the last year confirm and extend the notion that angiotensin II is a true cytokine prevalent at all stages of atherogenesis.