Cholesterol-induced upregulation of angiotensin II and its effects on monocyte-endothelial interaction and superoxide production

Lipid profiles and the risk of new-onset hypertension in a Chinese community-based cohort

BACKGROUND AND AIMS

Dyslipidemia and hypertension, key risk factors for cardiovascular disease, may share similar pathophysiological processes. A longitudinal association was reported between dyslipidemia and new-onset hypertension, but few data were published in Asian. We aimed to investigate the association of lipid profiles with new-onset hypertension in a Chinese community-based non-hypertensive cohort without lipid-lowering treatment (n = 1802).

METHODS AND RESULTS

New-onset hypertension was defined as any self-reported history of hypertension, systolic blood pressure ≥140 mmHg, or diastolic blood pressure ≥90 mmHg, or receiving antihypertensive medications at follow-up. Logistic regression models were used to evaluate the associations. Participants were aged 53.97 ± 7.49 years, 31.19% were men, and 64.54% with dyslipidemia. During a median of 2.30 years follow-up, the incidence of new-onset hypertension was 12.99%. Multivariate adjusted risks of new-onset hypertension increased with triglyceride increases (odds ratio [OR] = 1.14, 95% confidence interval [CI]: 1.03-1.27) and high-density lipoprotein cholesterol (HDL-C) decreases (OR = 0.47, 95% CI: 0.29-0.76) for one unit. However, threshold effects were observed for total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C) and non-HDL-C. Compared with subjects with hyperlipidemia, in those with normal concentrations of TC, LDL-C, and non-HDL-C increased risks of new-onset hypertension were observed with OR (95% CI) of 1.65 (1.10-2.46), 1.58 (1.07-2.33), and 1.57 (1.15-2.15) for one unit increasement, respectively, after adjusting for all covariates.

CONCLUSION

Higher TG and lower HDL-C increased the risk of new-onset hypertension, but for TC, LDL-C and non-HDLC, the risk of new-onset hypertension was increased only at normal concentrations in a Chinese community-based cohort.

Serum LDL cholesterol levels and new onset of arterial hypertension: an 8-year follow-up

BACKGROUND

Serum cholesterol has been demonstrated to correlate with blood pressure values; therefore, abnormal levels of serum cholesterol might contribute to the development of hypertension. The aim of this study was to assess the new onset of hypertension over a period of 8 years in a pharmacologically untreated population sample in normo- and hypercholesterolemic individuals.

DESIGN

1864 Caucasian subjects with baseline blood pressure values <140/90 mmHg were subdivided into two different groups, according to LDL cholesterol changes observed over a period of 8 years. Group 1 included subjects whose LDL cholesterol levels remained or decreased within the normal range, while Group 2 included those whose LDL cholesterol levels were persistently increased above the normal range. The 8-year incidence of new-onset hypertension was 7·1% in Group 1 and 13·8% in Group 2 (P = 0·02), after adjustment for the main confounding risk factors. The difference between Groups 1 and 2 was confirmed in men (8·2 vs. 13·1%, P = 0·04) and women (6·1. vs. 14·5%, P = 006), as well as in subjects younger than 65 years (5·7 vs. 10·9%; P = 0·011), but not in older ones.

CONCLUSIONS

Baseline serum LDL cholesterol levels are related to the rate of new-onset hypertension in patients with normal or marginally elevated blood pressure values.

Rate of control of LDL cholesterol and incident hypertension requiring antihypertensive treatment in hypercholesterolemic subjects in daily clinical practice

INTRODUCTION

Preliminary evidence suggests that hypercholesterolemia is associated to an increased risk to develop hypertension. We aimed at evaluating the association between low-density lipoprotein cholesterol (LDL-C) level and incidence of new onset of hypertension in a large population sample.

MATERIALS AND METHODS

A population-based cohort of 20,074 subjects with at least one LDL-C measurement between July 2006 and June 2007 and free of antihypertensive treatment (AHT) at baseline was followed from the LDL-C date until death or 31 December 2009.

RESULTS

During the follow-up, 10.7% of patients with LDL-C < 130 mg/dL, 13.2% of patients with LDL-C between 130 and 159 mg/dL, 12.2% of patients with LDL-C between 160 and 189 mg/dL, and 13.9% of patients with LDL-C ≥ 190 mg/dL had new-onset hypertension requiring the initiation of AHT. Compared with the LDL-C < 130 mg/dL group, the hazard ratio (HR) of initiation of AHT increased among those with LDL-C level between 130 and 159 mg/dL (HR 1.23; 95% CI: 1.08-1.40), those with LDL-C level between 160 and 189 mg/dL (HR 1.24; 95% CI: 1.01-1.51), and those with LDL-C ≥ 190 mg/dL (HR 1.45; 95% CI: 1.11-1.89).

CONCLUSION

A better control of cholesterolemia seems to be associated to a lower incidence of new-onset of hypertension requiring AHT in a large cohort of general population.

Renal and metabolic disorders depend on the renin-angiotensin system in Lyon hypertensive rats associated with diabetes

BACKGROUND

In Lyon genetically hypertensive (LH) rats with diabetes, the effects of angiotensin converting enzyme (ACE) inhibition with perindopril on the prevention of dyslipidemia and proteinuria were evaluated by comparison with a nonspecific antihypertensive treatment.

METHODS

Diabetes was induced in 2-day-old male LH rats by intraperitoneal injection of streptozotocin (75 mg/kg). Glucose tolerance (glucose 2 g/kg by gavage), blood pressure (BP), plasma lipids, and urinary protein excretion were studied in: (i) untreated diabetic LH rats, (ii) diabetic LH rats treated from 8 to 16 weeks of age with oral perindopril at a low dose (0.01 mg/kg/day), (iii) similar rats treated with oral perindopril for the same duration at a high dose (1 mg/kg/day), and (iv) similar rats treated for the same duration with a triple therapy regimen consisting of hydralazine, hydrochlorothiazide, and reserpine (75, 15, and 0.75 mg/kg/day, respectively).

RESULTS

The neonatal administration of streptozotocin in LH rats increased nonfasting glycemia and induced a marked glucose intolerance which was accompanied by further increases in BP, plasma cholesterol, and urinary protein excretion. None of the treatments was able to modify glucose tolerance in diabetic LH rats. The low dose of perindopril was ineffective in the prevention of hypertension, dyslipidemia, and proteinuria in diabetic LH rats, while the high dose of perindopril normalized the BP, reduced the plasma lipids, and lowered the proteinuria. However, in spite of significant reduction in BP, the triple therapy failed to improve dyslipidemia and proteinuria; on the contrary, the therapy worsened these two conditions.

CONCLUSIONS

In diabetic LH rats, only ACE inhibition is of benefit to the kidney and lipidemia, thereby demonstrating that antihypertensive regimens may differ in their capacity to protect the target organs and lipid metabolism in a diabetic setting.

Hypercholesterolemia, not metabolic syndrome, related to adhesion of monocytes to cultured endothelium in nondiabetic subjects

The interaction of leukocytes and endothelium plays an important role in the development of atherosclerosis. Previous studies found that adhesion of leukocytes to endothelium is greater in subjects with hypercholesterolemia. It is not clear if metabolic syndrome, a contributing risk factor of cardiovascular disease, is related to this adhesion. Therefore, we conducted a study, in which 48 nondiabetic subjects were enrolled, to determine the relationship between leukocyte adhesion and the components of metabolic syndrome. After a 12-hour overnight fast, subjects' fasting blood was obtained for measurement of lipoprotein concentrations and glucose and insulin levels. Results of the number of monocyte adhesion to human umbilical vein endothelial cells were divided into high monocyte adhesion group and low monocyte adhesion group (n=24 in each group). Plasma concentrations of total cholesterol (245 +/- 5 vs 229+/- 4 mg/dL, P=.021) and low-density lipoprotein cholesterol (LDL-C) (162+/- 4 vs 146+/- 3 mg/dL, P=.003) were both higher in the high monocyte adhesion group than in the low monocyte adhesion group. Monocyte adhesion was significantly correlated to plasma concentrations of LDL-C (r=0.407, P=.002) but not to the total cholesterol (r=0.202, P=.085). However, there was no difference in monocyte adhesion to endothelium between subjects with or without metabolic syndrome, based on the modified criteria from the Adult Treatment Panel III of the National Cholesterol Education Program. Insulin resistance index, presented as homeostasis model assessment insulin resistance, and glucose or insulin responses to oral glucose tolerance test were similar between groups. Our study demonstrated that monocyte adhesion to endothelium has a stronger relationship with the plasma concentration LDL-C than with characteristics of metabolic syndrome.

Caveolin interacts with the angiotensin II type 1 receptor during exocytic transport but not at the plasma membrane

The mechanisms involved in angiotensin II type 1 receptor (AT1-R) trafficking and membrane localization are largely unknown. In this study, we examined the role of caveolin in these processes. Electron microscopy of plasma membrane sheets shows that the AT1-R is not concentrated in caveolae but is clustered in cholesterol-independent microdomains; upon activation, it partially redistributes to lipid rafts. Despite the lack of AT1-R in caveolae, AT1-R.caveolin complexes are readily detectable in cells co-expressing both proteins. This interaction requires an intact caveolin scaffolding domain because mutant caveolins that lack a functional caveolin scaffolding domain do not interact with AT1-R. Expression of an N-terminally truncated caveolin-3, CavDGV, that localizes to lipid bodies, or a point mutant, Cav3-P104L, that accumulates in the Golgi mislocalizes AT1-R to lipid bodies and Golgi, respectively. Mislocalization results in aberrant maturation and surface expression of AT1-R, effects that are not reversed by supplementing cells with cholesterol. Similarly mutation of aromatic residues in the caveolin-binding site abrogates AT1-R cell surface expression. In cells lacking caveolin-1 or caveolin-3, AT1-R does not traffic to the cell surface unless caveolin is ectopically expressed. This observation is recapitulated in caveolin-1 null mice that have a 55% reduction in renal AT1-R levels compared with controls. Taken together our results indicate that a direct interaction with caveolin is required to traffic the AT1-R through the exocytic pathway, but this does not result in AT1-R sequestration in caveolae. Caveolin therefore acts as a molecular chaperone rather than a plasma membrane scaffold for AT1-R.

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.