Beneficial Effects of Pulmonary Vasodilators on Pre-Capillary Pulmonary Hypertension in Patients with Chronic Kidney Disease on Hemodialysis.

BACKGROUND: In patients with chronic kidney disease (CKD) on hemodialysis, comorbid pulmonary hypertension (PH) aggravates exercise tolerance and eventually worsens the prognosis. The treatment strategy for pre-capillary PH, including combined pre- and post-capillary PH (Cpc-PH), has not been established. OBJECTIVES: This study aimed to evaluate the impact of pulmonary vasodilators on exercise tolerance and pulmonary hemodynamics in patients with CKD on hemodialysis. METHODS AND RESULTS: The medical records of 393 patients with suspected PH who underwent right heart catheterization were reviewed. Of these, seven patients had isolated pre-capillary PH and end-stage CKD on hemodialysis. Pulmonary vasodilators decreased pulmonary vascular resistance from 5.9 Wood units (interquartile range (IQR), 5.5-7.6) at baseline to 3.1 Wood units (IQR, 2.6-3.3) post-treatment (p = 0.02) as well as increased pulmonary capillary wedge pressure from 10 mmHg (IQR, 7-11) to 11 mmHg (IQR, 8-16) (p = 0.04). Pulmonary vasodilators increased the World Health Organization functional class I or II from 0% to 100% (p = 0.0002) and the 6 min walk distance from 273 m (IQR, 185-365) to 490 m (IQR, 470-550) (p = 0.03). CONCLUSIONS: Pulmonary vasodilators for PH in patients with CKD on hemodialysis decrease pulmonary vascular resistance and eventually improve exercise tolerance. Pulmonary vasodilators may help hemodialysis patients with pre-capillary PH, although careful management considering the risk of pulmonary edema is required.

Increased Lung Uric Acid Deteriorates Pulmonary Arterial Hypertension.

Background Recent studies have demonstrated that uric acid (UA) enhances arginase activity, resulting in decreased NO in endothelial cells. However, the role of lung UA in pulmonary arterial hypertension (PAH) remains uncertain. We hypothesized that increased lung UA level contributes to the progression of PAH. Methods and Results In cultured human pulmonary arterial endothelial cells, voltage-driven urate transporter 1 (URATv1) gene expression was detected, and treatment with UA increased arginase activity. In perfused lung preparations of VEGF receptor blocker (SU5416)/hypoxia/normoxia-induced PAH model rats, addition of UA induced a greater pressure response than that seen in the control and decreased lung cGMP level. UA-induced pressor responses were abolished by benzbromarone, a UA transporter inhibitor, or L-norvaline, an arginase inhibitor. In PAH model rats, induction of hyperuricemia by administering 2% oxonic acid significantly increased lung UA level and induced greater elevation of right ventricular systolic pressure with exacerbation of occlusive neointimal lesions in small pulmonary arteries, compared with nonhyperuricemic PAH rats. Administration of benzbromarone to hyperuricemic PAH rats significantly reduced lung UA levels without changing XOR (xanthine oxidoreductase) activity, and attenuated right ventricular systolic pressure increase and occlusive lesion development. Topiroxostat, a XOR inhibitor, significantly reduced lung XOR activity in PAH rats, with no effects on increase in right ventricular systolic pressure, arterial elastance, and occlusive lesions. XOR-knockout had no effects on right ventricular systolic pressure increase and arteriolar muscularization in hypoxia-exposed mice. Conclusions Increased lung UA per se deteriorated PAH, whereas XOR had little impact. The mechanism of increased lung UA may be a novel therapeutic target for PAH complicated with hyperuricemia.

Chronic Inhibition of Toll-Like Receptor 9 Ameliorates Pulmonary Hypertension in Rats.

Background Recent accumulating evidence suggests that toll-like receptor 9 (TLR9) is involved in the pathogenesis of cardiovascular diseases. However, its role in pulmonary hypertension remains uncertain. We hypothesized that TLR9 is involved in the development of pulmonary hypertension. Methods and Results A rat model of monocrotaline-induced pulmonary hypertension was used to investigate the effects of TLR9 on hemodynamic parameters, vascular remodeling, and survival. Monocrotaline-exposed rats significantly showed increases in plasma levels of mitochondrial DNA markers, which are recognized by TLR9, TLR9 activation in the lung, and interleukin-6 mRNA level in the lung on day 14 after monocrotaline injection. Meanwhile, monocrotaline-exposed rats showed elevated right ventricular systolic pressure, total pulmonary vascular resistance index and vascular remodeling, together with macrophage accumulation on day 21. In the preventive protocol, administration (days -3 to 21 after monocrotaline injection) of selective (E6446) or nonselective TLR9 inhibitor (chloroquine) significantly ameliorated the elevations of right ventricular systolic pressure and total pulmonary vascular resistance index as well as vascular remodeling and macrophage accumulation on day 21. These inhibitors also significantly reduced NF-κB activation and interleukin-6 mRNA levels to a similar extent. In the short-term reversal protocol, E646 treatment (days 14-17 after monocrotaline injection) almost normalized NF-κB activation and interleukin-6 mRNA level, and reduced macrophage accumulation. In the prolonged reversal protocol, E6446 treatment (days 14-24 after monocrotaline injection) reversed total pulmonary vascular resistance index and vascular remodeling, and improved survival in monocrotaline-exposed rats. Conclusions TLR9 is involved in the development of pulmonary hypertension concomitant via activation of the NF-κB‒IL-6 pathway. Inhibition of TLR9 may be a novel therapeutic strategy for pulmonary hypertension.