Exhaled nitric oxide measurement to monitor pulmonary hypertension in a pneumonectomy-monocrotaline rat model

The Nitric Oxide Pathway in Pulmonary Arterial Hypertension: Pathomechanism, Biomarkers and Drug Targets

The altered Nitric Oxide (NO) pathway in the pulmonary endothelium leads to increased vascular smooth muscle tone and vascular remodelling, and thus contributes to the development and progression of pulmonary arterial hypertension (PAH). The pulmonary NO signalling is abrogated by the decreased expression and dysfunction of the endothelial NO synthase (eNOS) and the accumulation of factors blocking eNOS functionality. The NO deficiency of the pulmonary vasculature can be assessed by detecting nitric oxide in the exhaled breath or measuring the degradation products of NO (nitrite, nitrate, S-nitrosothiol) in blood or urine. These non-invasive biomarkers might show the potential to correlate with changes in pulmonary haemodynamics and predict response to therapies. Current pharmacological therapies aim to stimulate pulmonary NO signalling by suppressing the degradation of NO (phosphodiesterase- 5 inhibitors) or increasing the formation of the endothelial cyclic guanosine monophosphate, which mediates the downstream effects of the pathway (soluble guanylate cyclase sensitizers). Recent data support that nitrite compounds and dietary supplements rich in nitrate might increase pulmonary NO availability and lessen vascular resistance. This review summarizes current knowledge on the involvement of the NO pathway in the pathomechanism of PAH, explores novel and easy-to-detect biomarkers of the pulmonary NO.

Combined oral administration of L-arginine and tetrahydrobiopterin in a rat model of pulmonary arterial hypertension

Alterations in the nitric oxide (NO) pathway play a major role in pulmonary arterial hypertension (PAH). L-arginine (LA) and tetrahydrobiopterin (BH₄) are main substrates in the production of NO, which mediates pulmonary vasodilation. Administration of either LA or BH₄ decrease pulmonary artery pressure (PAP). A combined administration of both may have synergistic effects in the therapy of PAH. In a telemetrically monitored model of unilateral pneumonectomy and monocrotaline-induced PAH, male Sprague-Dawley rats received either LA (300 mg/kg; n = 15), BH₄ (20 mg/kg; n = 15), the combination of LA and BH₄ (300 mg/kg, 20 mg/kg; n = 15), or vehicle (control group; n = 10) from day 28 after monocrotaline induction. Therapy was orally administered once daily over consecutive 14 days. LA, BH₄, or both equally lowered PAP, increased pulmonary vascular elasticity, restored spontaneous locomotoric activity, prevented body weight loss and palliated small vessel disease of severely pulmonary hypertensive rats. BH₄ substitution lowered asymmetric dimethylarginine levels sustainably at 60 min after administration and downregulated endothelial NO synthase mRNA expression. No significant survival, macro- and histomorphologic or hemodynamic differences were found between therapy groups at the end of the study period. Administration of LA and BH₄ both mediated a decrease of mean PAP, attenuated right ventricular hypertrophy and small vessel disease in monocrotaline-induced pulmonary hypertensive rats, though a combined administration of both substances did not reveal any synergistic therapy effects in our animal model.

A review of recent developments and applications of morphometry/stereology in lung research

Design-based stereology is the gold standard of morphometry in lung research. Here, we analyze the current use of morphometric and stereological methods in lung research and provide an overview on recent methodological developments and biological observations made by the use of stereology. Based on this analysis we hope to provide useful recommendations for a good stereological practice to further the use of advanced and unbiased stereological methods.

Application of nitric oxide measurements in clinical conditions beyond asthma

Fractional exhaled nitric oxide (FeNO) is a convenient, non-invasive method for the assessment of active, mainly Th2-driven, airway inflammation, which is sensitive to treatment with standard anti-inflammatory therapy. Consequently, FeNO serves as a valued tool to aid diagnosis and monitoring in several asthma phenotypes. More recently, FeNO has been evaluated in several other respiratory, infectious, and/or immunological conditions. In this short review, we provide an overview of several clinical studies and discuss the status of potential applications of NO measurements in clinical conditions beyond asthma.