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Interleukin-6 Causes Mild Pulmonary Hypertension and Augments Hypoxia-Induced Pulmonary Hypertension in Mice

Pulmonary arterial hypertension (PAH) is a severe cardiopulmonary dysfunctional disease, characterized by progressive vascular remodeling. Inflammation is an increasingly recognized feature of PAH, which is important for the initiation and maintenance of vascular remodeling. High levels of various inflammatory mediators have been documented in both PAH patients and experimental models of PAH. Similarly, multiple immune cells were found to accumulate in and around the wall of remodeled pulmonary vessels and in the vicinity of plexiform lesions, respectively. On the other hand, inflammation is also a bridge from autoimmune diseases to PAH. Autoimmune diseases always lead to chronic inflammation, characterized by the low-level persistent infiltration of immune cells, and elevated levels of several pro-inflammatory cytokines and chemokines. In addition, circulating autoantibodies are found in the peripheral blood of patients, indicating a possible role of autoimmunity in the pathogenesis of PAH. Thus, anti-inflammatory and immunotherapy might be new strategies to prevent or even reverse the process of PAH. Many anti-inflammatory agents and immunotherapies have been confirmed in animal models while some clinical trials employing immunotherapies are completed or currently underway. Here, we review pathological mechanisms associated with inflammation and immunity in the development of PAH, and discuss potential interventions for the treatment of PAH.

Cardiovascular disease (CVD), especially ischemic heart disease and stroke, is the major cause of death worldwide, accounting for more than one-third of all deaths annually. Hypertension is the most prevalent and modifiable risk factor of CVD-related deaths. The same is true for obesity, which is currently being recognized as a major global epidemic. The prevalence of obesity in the United States has increased dramatically, from 13.4% in 1960 to 36.5% in 2014, with as much as 70.7% of the American adult population being overweight or obese (CDC). Epidemiological studies have shown that obesity predisposes to hypertension and CVD – with the relationship between markers of obesity and blood pressure being almost linear across different populations. In this review, we discuss systemic and pulmonary hypertension in the context of obesity.

Cardiovascular fibrosis refers to the scar tissue that develops in the injured heart and blood vessels from an aberrant wound healing response to organ injury or insult. Established fibrosis becomes a hallmark of chronic disease progression and a key contributor to tissue stiffness and dysfunction, which ultimately leads to heart failure. As wound healing and fibrotic responses to myocardial injury are multifactorial processes, current therapies that only target specific contributing factors to disease pathogenesis offer limited overall anti-fibrotic efficacy. As such, recent attention has turned to targeting the body’s immune system, which orchestrates the wound healing response to tissue injury. This review focuses on the increasing body of work that has identified the NLRP3 inflammasome, a multiprotein oligomer complex responsible for activation of inflammatory responses via its production of IL-1β and IL-18, as an immune system-initiated facilitator of cardiovascular healing, but also an important contributor to tissue scarring following its persistent activation. The review summarises the factors that can elicit priming and activation of the inflammasome complex, how the activated inflammasome complex contributes to cardiovascular pathophysiology and fibrosis progression, and the molecular mechanisms involved from various cell culture and animal model studies that have utilised genetic deletion or pharmacological inhibition of specific components of the inflammasome. Finally, it outlines currently known and previously unrecognised cardiovascular receptors that may be pharmacologically targeted to ablate the contribution of the NLRP3 inflammasome to cardiovascular diseases characterised by fibrosis, by compounds that may be developed as effective adjunct therapies to current standard of care medication.

Pulmonary artery hypertension (PAH) is a chronic and deadly disease, for which effective medical treatments are lacking. Here, we investigated whether 2R,3R-dihydromyricetin (DHM) could prevent monocrotaline (MCT)-induced PAH in rats. The MCT-injected rats were treated with normal saline or DHM (100 mg/kg body weight/d) for 4 weeks, followed by measurements of right ventricular systolic pressure (RVSP), right ventricular hypertrophy index (RVHI), pulmonary arterial remodeling (PAR), and expression levels of IL-6, TNF-α, and IL-10. In vitro, we assessed the role of DHM on IL-6-induced migration of primary human pulmonary arterial smooth muscle cells (HPASMCs). We found that DHM treatment attenuated changes in RVSP, RVHI, and PAR in MCT-injected PAH rats. The observed increase of IL-6 levels in PAH rats was inhibited by DHM treatment. In vitro, DHM pretreatment reduced IL-6-induced HPASMC migration. Furthermore, MCT- and IL-6-mediated increases in MMP9 and P-STAT3 (tyr705) PY-STAT3 levels were suppressed by DHM treatment in vivo and in vitro. These results suggest that DHM could prevent MCT-induced rat PAH and IL-6-induced HPASMC migration through a mechanism involving inhibiting of the STAT3/MMP9 axis.

Interleukin 6 (IL-6) is a multifunctional proinflammatory cytokine that is elevated in patients with pulmonary arterial hypertension (PAH). Single nucleotide polymorphisms in the promoter region of IL-6 have been reported to transcriptional regulate the expression of IL-6. The aim of the present study is to investigate the roles of two common polymorphisms (-572C/G [rs1800796] and -6331T/C [rs10499563]) of IL-6 in idiopathic PAH (IPAH). A total of 338 IPAH patients and 352 age- and gender-matched healthy controls were enrolled. Genotyping of the two polymorphisms was performed by polymerase chain reaction and direct sequencing. Serum IL-6 levels were determined by ELISA assay. The frequencies of -572C/G genotypes CC, CG, and GG were found to be 63.6%, 32.3%, and 4.1% in IPAH patients group and 51.7%, 39.5%, and 8.8% in the controls, respectively. Compared with the individuals carrying the common genotype CC, the individuals carrying the GG genotype had a decreased risk of IPAH (adjusted odds ratio, 0.40; 95% confidence interval, 0.20–0.77; P = .006). The CG genotype and G allele carriers (CG/GG genotypes) were also observed to be associated with decreased risks of IPAH. Moreover, we found that individuals harboring -572GG or GC genotype showed significantly lower IL-6 levels than those harboring the -572CC genotype. No association between -6331T/C polymorphism and risk of IPAH or IL-6 levels was found. These results suggest that IL-6 promoter polymorphism -572C/G, but not -6331T/C, is associated with serum IL-6 levels and risk of IPAH.