Cytokines, Interleukin-18, and the Genetic Determinants of Vascular Inflammation

Cytokines trigger disruption of endothelium barrier function and p38 MAP kinase activation in BMPR2-silenced human lung microvascular endothelial cells

The bone morphogenetic protein receptor II (BMPRII) signaling pathway is impaired in pulmonary arterial hypertension and mutations in the BMPR2 gene have been observed in both heritable and idiopathic pulmonary arterial hypertension. However, all BMPR2 mutation carriers do not develop pulmonary arterial hypertension, and inflammation could trigger the development of the disease in BMPR2 mutation carriers. Circulating levels and/or lung tissue expression of cytokines such as tumor necrosis factor-α or interleukin-18 are elevated in patients with pulmonary arterial hypertension and could be involved in the pathogenesis of pulmonary arterial hypertension. We consequently hypothesized that cytokines could trigger endothelial dysfunction in addition to impaired BMPRII signaling. Our aim was to determine whether impairment of BMPRII signaling might affect endothelium barrier function and adhesiveness to monocytes, in response to cytokines. BMPR2 was silenced in human lung microvascular endothelial cells (HLMVECs) using lentiviral vectors encoding microRNA-based hairpins. Effects of tumor necrosis factor-α and interleukin-18 on HLMVEC adhesiveness to the human monocyte cell line THP-1, adhesion molecule expression, endothelial barrier function and activation of P38MAPK were investigated in vitro. Stable BMPR2 silencing in HLMVECs resulted in impaired endothelial barrier function and constitutive activation of P38MAPK. Adhesiveness of BMPR2-silenced HLMVECs to THP-1 cells was enhanced by tumor necrosis factor-α and interleukin-18 through ICAM-1 adhesion molecule. Interestingly, tumor necrosis factor-α induced activation of P38MAPK and disrupted endothelial barrier function in BMPR2-silenced HLMVECs. Altogether, our findings showed that stable BMPR2 silencing resulted in impaired endothelial barrier function and activation of P38MAPK in HLMVECs. In BMPR2-silenced HLMVECs, cytokines enhanced adhesiveness capacities, activation of P38MAPK and impaired endothelial barrier function suggesting that cytokines could trigger the development of pulmonary arterial hypertension in a context of impaired BMPRII signaling pathway.

Macrophage-derived IL-18 and increased fibrinogen deposition are age-related inflammatory signatures of vascular remodeling

Aging has been associated with pathological vascular remodeling and increased neointimal hyperplasia. The understanding of how aging exacerbates this process is fundamental to prevent cardiovascular complications in the elderly. This study proposes a mechanism by which aging sustains leukocyte adhesion, vascular inflammation, and increased neointimal thickness after injury. The effect of aging on vascular remodeling was assessed in the rat balloon injury model using microarray analysis, immunohistochemistry, and LINCOplex assays. The injured arteries in aging rats developed thicker neointimas than those in younger animals, and this significantly correlated with a higher number of tissue macrophages and increased vascular IL-18. Indeed, IL-18 was 23-fold more abundant in the injured vasculature of aged animals compared with young rats, while circulating levels were similar in both groups of animals. The depletion of macrophages in aged rats with clodronate liposomes ameliorated vascular accumulation of IL-18 and significantly decreased neointimal formation. IL-18 was found to inhibit apoptosis of vascular smooth muscle cells (VSMC) and macrophages, thus favoring both the formation and inflammation of the neointima. In addition, injured arteries of aged rats accumulated 18-fold more fibrinogen-γ than those of young animals. Incubation of rat peritoneal macrophages with immobilized IL-18 increased leukocyte adhesion to fibrinogen and suggested a proinflammatory positive feedback loop among macrophages, VSMC, and the deposition of fibrinogen during neointimal hyperplasia. In conclusion, our data reveal that concentration changes in vascular cytokine and fibrinogen following injury in aging rats contribute to local inflammation and postinjury neointima formation.

Relationship between single nucleotide polymorphism of interleukin-18 and susceptibility to pulmonary tuberculosis in the Chinese Han population

Interleukin-18 (IL-18) is a multi-functional cytokine capable of inducing either Th1 or Th2 polarization depending on the immunologic milieu. IL-18 may influence the host response to Mycobacterium tuberculosis (M.tb) infection. To investigate the relationship between single nucleotide polymorphisms of the IL-18 and susceptibility to pulmonary tuberculosis in the Chinese Han population, the IL-18 gene was sequenced to detect polymorphisms and to examine the genotype frequencies in 300 patients and 702 healthy controls. DNA sequencing revealed three IL-18 variants: rs1946518, rs5744247, and rs549908. It also revealed that allele A of rs1946518 confers a 1.47-fold increased risk of developing tuberculosis (TB) (P = 0.0001, OR [95%CI] = 1.47 [1.21-1.78]), and that the C allele of rs5744247 confers a 0.77-fold decreased risk of disease (P = 0.01, R [95%CI] = 0.77 [0.632-0.937]). The genotypes rs1946518, rs5744247 and rs549908 were found to be significantly associated with TB. Estimation of the frequencies of haplotypes revealed a potential risk haplotype AGA (P = 0.01, OR [95%CI] = 1.41 [1.15-1.72]) and a protective haplotype CCA (P = 0.01, OR [95%CI] = 0.70 [0.57-0.85]) for TB. The present findings suggest that polymorphisms in the IL-18 gene may affect susceptibility to TB and increase the risk of developing the disease in the Chinese Han population.

Promoter polymorphism of interleukin-18 in angiographically proven coronary artery disease

Interleukin 18 (IL-18) is a pro-atherogenic cytokine associated with the occurrence of various cardiac complications. The IL-18 gene has a functional -137 G/C polymorphism (rs187238) in the promoter region. Using the ligase detection reaction-polymerase chain reaction, we genotyped a cohort of patients in Chinese Han population in Xiangfan region. Case patients of coronary artery disease and control patients were identified by coronary angiography. The plasma IL-18 concentrations were measured by ELISA. A significant increase of G allele or GG-genotype was observed in 241 case patients compared to 145 control individuals (frequency of G allele = 0.90 vs 0.83, p=0.004; frequency of GG-genotype = 0.81 vs 0.68, p = 0.005). In case patients, G allele carriers in multi-vessel disease patients had a higher occurrence rate when compared to single-vessel disease patients, but no significant difference was detected (frequency of G allele = 0.92 vs 0.88, p=0.107; frequency of GG-genotype = 0.84 vs 0.75, p = 0.089). IL-18 protein concentration of the -137GG genotype was much higher than concentration of the CG and CC genotype (case patients: 229.1+/-131.5 vs 122.7+/-73.6 pg/ml, P < 0.001; control patients: 65.9+/-31.6 vs 42.4+/-19.5 pg/ml, P < 0.001). To conclude, IL-18 promoter -137G/C polymorphism influences IL-18 levels and the occurrence of coronary artery disease, suggesting that IL-18 is causally involved in the development of atherosclerosis.

An interleukin-18 polymorphism is associated with reduced serum concentrations and better physical functioning in older people

BACKGROUND

The proinflammatory cytokine interleukin-18 (IL-18) is associated with major disabling conditions, although whether as byproduct or driver is unclear. The role of common variation in the IL-18 gene on serum concentrations and functioning in old age is unknown.

METHODS

We used 1671 participants aged 65-80 years from two studies: the InCHIANTI study and wave 6 of the Iowa-Established Populations for Epidemiological Study of the Elderly (EPESE). We tested three common polymorphisms against IL-18 concentration and measures of functioning.

RESULTS

In the InCHIANTI study, a 1 standard deviation increase in serum IL-18 concentrations was associated with an increased chance of being in the 20% of slowest walkers (odds ratio 1.45; 95% confidence interval, 1.17-1.80; p =.0007) and 20% of those with poorest function based on the Short Physical Performance Battery Score (odds ratio 1.52; 95% confidence interval, 1.22-1.89; p =.00016) in age sex adjusted logistic regression models. There was no association with Activities of Daily Living (p =.26) or Mini-Mental State Examination score (p =.66). The C allele of the IL-18 polymorphism rs5744256 reduced serum concentrations of IL-18 by 39 pmol/mL per allele (p =.00001). The rs5744256 single nucleotide polymorphism was also associated with shorter walk times in InCHIANTI (n = 662, p =.016) and Iowa-EPESE (n = 995, p =.026). In pooled ranked models rs5744256 was also associated with higher SPPB scores (n = 1671, p =.019). Instead of adjusting for confounders in the IL-18 walk time association, we used rs5744256 in a Mendelian randomization analysis: The association remained in instrumental variable models (p =.021).

CONCLUSION

IL-18 concentrations are associated with physical function in 65- to 80-year-olds. A polymorphism in the IL-18 gene alters IL-18 concentrations and is associated with an improvement in walk speed. IL-18 may play an active role in age-related functional impairment, but these findings need independent replication.

Inflammation, atherosclerotic burden and cardiovascular prognosis

BACKGROUND

The aim of this study was to evaluate the impact of various inflammatory markers on atherosclerotic burden and cardiovascular prognosis.

METHODS

In a prospective study 720 patients preceding coronary angiography were enrolled. In all patients carotid and leg arteries were examined using sonographic methods and C-reactive protein, fibrinogen, interleukin-18 (IL-18) and interleukin-6 have been determined. Patients were compared with regard to atherosclerotic burden: no clinically significant stenosis (N=57, 7.9%), coronary artery disease only (N=362, 50.3%), coronary artery disease with peripheral atherosclerosis (=multi-vascular atherosclerosis, N=301, 41.8%).

RESULTS

Follow-up data after a median of 6.5 years were available in 719 patients (99.9%), 75 patients (10.4%) died from cardiovascular causes. Presence of multi-vascular atherosclerosis, elevation of IL-18 and elevation of fibrinogen were independently related to cardiovascular death in a fully adjusted model Hazard ratio (95% confidence interval) 2.0 (1.2-3.5) for presence of multi-vascular atherosclerosis (P<0.01), 2.2 (1.2-3.9) for high fibrinogen (P<0.01) and 2.8 (1.6-4.9) for high IL-18 (P<0.0001)). Fibrinogen was achieved as independent predictor for both, mortality and atherosclerotic burden, whereas IL-18 was not related to atherosclerotic burden.

CONCLUSIONS

IL-18 was an independent predictor for future cardiovascular death but was not associated with extent of atherosclerosis, whereas fibrinogen was independently related to cardiovascular death and extent of disease.