Essential hypertension: is there a role for inflammatory mechanisms?

Periodontitis and blood pressure: the concept of dental hypertension

Chronic periodontitis is a common inflammatory disorder that is being contemplated as a risk factor for atherosclerotic complications. Current epidemiological evidence also supports its potential association with increases in blood pressure levels and hypertension prevalence. Furthermore, data from cross-sectional studies suggest that in hypertensive subjects periodontitis may enhance the risk and degree of target organ damage. A possible pathogenetic background of an effect of periodontitis on blood pressure should include the systemic generalization of the local oral inflammation, the role of the host immune response, the direct microbial effect on the vascular system and alterations in endothelial function. Inversely, the concept of hypertension unfavorably affecting periodontal tissues cannot be excluded. The two conditions share multiple common risk factors that should be readily controlled for when assessing a possible association. Thoroughly designed prospective and interventional trials are needed in order to determine the impact of periodontitis on blood pressure regulation and incident hypertension and its integration in the clinical approach of both dental and hypertensive patients.

Sphingosine-1-phosphate-induced inflammation involves receptor tyrosine kinase transactivation in vascular cells: upregulation in hypertension

Sphingosine-1-phosphate (S1P), a multifunctional phospholipid, regulates vascular cell function. Whether S1P influences vascular inflammatory responses, particularly in hypertension, is unclear. We tested the hypothesis that S1P is a proinflammatory mediator signaling through receptor tyrosine kinase transactivation and that responses are amplified in vascular smooth muscle cells from stroke-prone spontaneously hypertensive rats (SHRSPs), a model in which we demonstrated Edg1 (S1P1 receptor) to be a candidate gene for salt-sensitive hypertension. Vascular smooth muscle cell from Wistar-Kyoto rats and SHRSPs were studied. S1P receptor subtypes, S1P1 and S1P2, were similarly expressed in Wistar-Kyoto rats and SHRSPs. S1P induced phosphorylation of epidermal growth factor receptor and platelet-derived growth factor and activation of p38 mitogen-activated protein kinase and c-Jun N-terminal kinase, with amplified effects in SHRSPs versus Wistar-Kyoto rats. Inhibition of epidermal growth factor receptor and platelet-derived growth factor (with AG1478 and AG1296, respectively) abolished S1P-induced phosphorylation of p38 mitogen-activated protein kinase and c-Jun N-terminal kinase in Wistar-Kyoto rats with variable effects in SHRSPs. Vascular smooth muscle cell inflammation was evaluated by expression of adhesion molecules and functional responses assessed by monocyte adhesion. S1P stimulated expression of intercellular adhesion molecule 1 and vascular cell adhesion protein 1 and promoted monocyte adhesion, particularly in SHRSP cells. S1P-mediated inflammation was blunted by AG1478 and AG1296 in SHRSP cells. VPC23019, a S1P1 receptor antagonist, inhibited S1P-induced mitogen-activated protein kinase phosphorylation, intercellular adhesion molecule 1 and vascular cell adhesion protein 1 expression, and monocyte adhesion. Our data indicate that molecular processes underlying vascular inflammation and cell adhesion in SHRSPs involve S1P/S1P1 receptors and phosphorylation of receptor tyrosine kinases. We identify a novel pathway linking S1P/S1P1 receptors to specific proinflammatory signaling pathways through epidermal growth factor receptor and platelet-derived growth factor transactivation, a process that is upregulated in SHRSPs. Such molecular events may contribute to vascular inflammation in hypertension.

The association of plasma resistin with dietary sodium manipulation, the renin-angiotensin-aldosterone system, and 25-hydroxyvitamin D3 in human hypertension

OBJECTIVE

Both resistin and vitamin D have been associated with the renin-angiotensin-aldosterone system (RAAS). We investigated the association between resistin and the RAAS, and resistin and vitamin D under controlled dietary sodium conditions.

DESIGN

Retrospective cross-sectional study of subjects from the HyperPATH Consortium, who were maintained in high dietary sodium (HS) and low dietary sodium (LS) balance for 1 week each.

PATIENTS

Caucasian subjects with hypertension (n=177).

MEASUREMENTS

25-Hydroxyvitamin D (25[OH]D) levels were used to assess vitamin D status. Plasma resistin and RAAS measures were evaluated on each dietary intervention.

RESULTS

Resistin levels were significantly higher in LS, where RAAS activity was high, when compared with HS balance, where RAAS activity was suppressed (6.36 vs 5.86 μg/l, P < 0.0001); however, resistin concentrations were not associated with plasma renin activity or serum aldosterone on either diet. 25(OH)D levels were positively and independently associated with resistin in both dietary conditions (HS: β=0.400, P-trend=0.027; LS: β=0.540, P-trend=0.014).

CONCLUSIONS

Dietary sodium loading reduced resistin levels, possibly by suppressing the RAAS; however, circulating RAAS components were not related to resistin concentrations within each specific dietary sodium condition. 25(OH)D was positively associated with resistin and may be involved in resistin regulation through an unknown mechanism. Further studies to understand resistin regulation in human hypertension better are warranted.

Uric acid levels and atrial fibrillation in hypertensive patients

OBJECTIVE

Uric acid (UA) is a cardiovascular risk marker associated with oxidative stress and inflammation. Recently, atrial fibrillation (AF) has been associated with inflammation and oxidative stress. The objective of this observational study was to investigate the association between UA levels and AF in hypertensive patients.

METHODS

Consecutive patients with hypertension were screened. We excluded subjects with coronary artery disease, congestive heart failure, diabetes, valvular heart disease, congenital heart disease, cardiomyopathy, renal failure, inflammatory conditions, thyroid dysfunction, respiratory diseases, and those who were taking drugs that affect UA metabolism (apart from diuretics). The final study population consisted of 451 patients. Fifty of them (11%) had AF (paroxysmal: 38; persistent: 8; permanent: 4). Demographic, clinical, laboratory, and echocardiographic characteristics were carefully recorded.

RESULTS

After univariate analysis, age, duration of hypertension, serum creatinine, serum UA, left atrial diameter (LAD), interventricular septum thickness, and left ventricular posterior wall thickness were significantly increased in patients with AF compared with non-AF patients, while the estimated glomerular filtration (eGFR) level was much lower in patients with AF than in those without AF. After multivariate logistic regression analysis, the independent predictors of AF were UA (OR: 1.008; 95% CI: 1.003-1.013, p=0.002) and LAD (OR: 1.160; 95% CI: 1.068-1.260; p<0.001).

CONCLUSION

We demonstrated an independent association between increased serum UA levels and AF in hypertensive patients. Undoubtedly, larger studies in different populations should further examine this potential association as well as the underlying pathophysiological mechanisms.

Pre-eclampsia: fitting together the placental, immune and cardiovascular pieces

The success of pregnancy is a result of countless ongoing interactions between the placenta and the maternal immune and cardiovascular systems. Pre-eclampsia is a serious pregnancy complication that arises from multiple potential aberrations in these systems. The pathophysiology of pre-eclampsia is established in the first trimester of pregnancy, when a range of deficiencies in placentation affect the key process of spiral artery remodelling. As pregnancy progresses to the third trimester, inadequate spiral artery remodelling along with multiple haemodynamic, placental and maternal factors converge to activate the maternal immune and cardiovascular systems, events which may in part result from increased shedding of placental debris. As we understand more about the pathophysiology of pre-eclampsia, it is becoming clear that the development of early- and late-onset pre-eclampsia, as well as intrauterine growth restriction (IUGR), does not necessarily arise from the same underlying pathology.

Ribonucleic acid interference knockdown of interleukin 6 attenuates cold-induced hypertension

The purpose of this study was to determine the role of the proinflammatory cytokine interleukin (IL) 6 in cold-induced hypertension. Four groups of male Sprague-Dawley rats were used (6 rats per group). After blood pressure was stabilized, 3 groups received intravenous delivery of adenoassociated virus carrying IL-6 small hairpin RNA (shRNA), adenoassociated virus carrying scrambled shRNA, and PBS, respectively, before exposure to a cold environment (5 degrees C). The last group received PBS and was kept at room temperature (25 degrees C, warm) as a control. Adenoassociated virus delivery of IL-6 shRNA significantly attenuated cold-induced elevation of systolic blood pressure and kept it at the control level for < or =7 weeks (length of the study). Chronic exposure to cold upregulated IL-6 expression in aorta, heart, and kidneys and increased macrophage and T-cell infiltration in kidneys, suggesting that cold exposure increases inflammation. IL-6 shRNA delivery abolished the cold-induced upregulation of IL-6, indicating effective silence of IL-6. Interestingly, RNA interference knockdown of IL-6 prevented cold-induced inflammation, as evidenced by a complete inhibition of tumor necrosis factor-alpha expression and leukocyte infiltration by IL-6 shRNA. RNA interference knockdown of IL-6 significantly decreased the cold-induced increase in vascular superoxide production. It is noted that IL-6 shRNA abolished the cold-induced increase in collagen deposition in the heart, suggesting that inflammation is involved in cold-induced cardiac remodeling. Cold exposure caused glomerular collapses, which could be prevented by knockdown of IL-6, suggesting an important role of inflammation in cold-induced renal damage. In conclusion, cold exposure increased IL-6 expression and inflammation, which play critical roles in the pathogenesis of cold-induced hypertension and cardiac and renal damage.