Vasodilatory effect of the stable vasoactive intestinal peptide analog RO 25-1553 in murine and rat lungs

Abstract

Rationale: Stable analogs of vasoactive intestinal peptide (VIP) have been proposed as novel line of therapy in chronic obstructive pulmonary disease (COPD) based on their bronchodilatory and anti-inflammatory effects. We speculated that VIP analogs may provide additional benefits in that they exert vasodilatory properties in the lung, and tested this hypothesis in both ex vivo and in vivo models.

Methods: In isolated perfused mouse lungs and in an in vivo rat model, pulmonary blood vessels were preconstricted by hypoxia and hemodynamic changes in response to systemic (ex vivo) or inhaled (in vivo) administration of the cyclic VIP analog RO 25-1553 were determined.

Results: In mouse lungs, RO 25-1553 reduced intrinsic vascular resistance at normoxia, and attenuated the increase in pulmonary artery pressure in response to acute hypoxia. Consistently, inhalation of RO 25-1553 (1 mg · mL(-1) for 3 min) caused an extensive and sustained (> 60 min) inhibition of the pulmonary arterial pressure increase in response to hypoxia in vivo that was comparable to the effects of inhaled sildenafil. This effect was not attributable to systemic cardiovascular effects of RO 25-1553, but to a lung specific reduction in pulmonary vascular resistance, while cardiac output and systemic arterial hemodynamics remained unaffected. No adverse effects of RO 25-1553 inhalation on pulmonary gas exchange, ventilation-perfusion matching, or lung fluid content were detected.

Conclusion: Our findings demonstrate that inhaled delivery of the stable VIP analog RO 25-1553 induces a potent and sustained vasodilatory effect in the pulmonary circulation with no detectable adverse effects. Therapeutic inhalation of RO 25-1553 may provide vascular benefits in addition to its reported anti-inflammatory and bronchodilatory effects in COPD, yet caution is warranted given the overall poor results of vasodilator therapies for pulmonary hypertension secondary to COPD in a series of recent clinical trials.

Figure 1. RO 25-1553 attenuates HPV in isolated murine lungs.

A) Representative tracings of pulmonary arterial pressure (PAP; lower panel) in isolated mouse lungs perfused in the absence (control) or presence of RO 25-1553 (1 mg·mL⁻¹) during stepwise changes in lung perfusion (Q; upper panel) at normoxia (21% O2) or hypoxia (1% O2). B) Group data showing the increase in pulmonary artery pressure (ΔPAP) relative to baseline measured 10 min after the change from normoxic (21% O₂) to hypoxic (1% O₂) ventilation in isolated mouse lungs perfused with buffer alone (control), with RO 25-1553 at final concentrations of 0.01, 0.1 or 1 mg·mL⁻¹, and in lungs perfused with sildenafil (100 nMol·L⁻¹) as positive control. C) Non-linear regression analysis according to the distensible vessel model yields representative pressure-flow (P-Q) curves for lungs perfused in the absence (control) or presence of RO 25-1553 (1 mg·mL⁻¹) at normoxia and hypoxia. The pressure at Q = 0 ml·kg⁻¹·min⁻¹ reflects the LAP which was set to 2 mmHg, while the corresponding slope of the P-Q curve reflects R₀. D) Group data showing intrinsic vascular resistance R₀ at normoxia (21% O₂) or hypoxia (1% O₂) in isolated mouse lungs perfused with buffer alone (control), with RO 25-1553 at final concentrations of 0.01, 0.1 or 1 mg·mL⁻¹, and in lungs perfused with sildenafil (100 nMol·L⁻¹) as positive control. Group data are means±SEMs; * p<0.05 vs. control, # p<0.05 vs. normoxia, n = 8 experiments each.

Figure 2. Inhaled RO 25-1553 attenuates HPV in the absence of systemic cardiovascular effects in vivo.

Group data showing A) mean pulmonary artery pressure (PAP), B) pulmonary vascular resistance (PVR), and C) mean systemic arterial pressure (AP) in rats at normoxic baseline (t = –25 min), after switch to hypoxic ventilation (11% O₂, open symbols) or during continued normoxic ventilation (21% O₂, black symbols), respectively (t = –10 min), and 5, 30 and 60 min following a 3 min inhalation of either 0.9% NaCl (circles), RO 25-1553 (1 mg·mL⁻¹; triangles) or sildenafil (10 mg·mL⁻¹; squares). Interval of hypoxic ventilation (for hypoxia groups) is indicated by dashed line, time of drug inhalation (t = 0 min) by arrow. Lines connecting individual data points serve assignment to the different study groups and do not reflect exact time course of parameters. Data are means±SEMs; * p<0.05 vs. corresponding normoxia group, # p<0.05 vs. NaCl group under similar ventilation; n = 8 experiments each.

Figure 3. Inhaled RO 25-1553 does not impair gas exchange or ventilation-perfusion matching in vivo.

Group data showing A) arterial partial pressure of O₂ (PaO₂), B) arterial partial pressure of CO₂ (PaCO₂), and C) pulmonary shunt fraction (Qs/Qt) in rats at normoxic baseline (t = –25 min), after switch to hypoxic ventilation (11% O₂, open symbols) or during continued normoxic ventilation (21% O₂, black symbols), respectively (t = –10 min), and 60 min following a 3 min inhalation of either 0.9% NaCl (circles), RO 25-1553 (1 mg·mL⁻¹; triangles) or sildenafil (10 mg·mL⁻¹; squares). Interval of hypoxic ventilation (for hypoxia groups) is indicated by dashed line, time of drug inhalation (t = 0 min) by arrow. Lines connecting individual data points serve assignment to the different study groups and do not reflect exact time course of parameters. Data are means±SEMs; * p<0.05 vs. corresponding normoxia group; n = 8 experiments each.

Figure 4. Inhaled RO 25-1553 does not increase lung water content in vivo.

Group data showing lung wet-to-dry weight ratio as a measure of lung edema in rats after normoxic (21% O₂, black bars) or hypoxic (11% O₂, open bars) ventilation for 70 min and a 3 min inhalation of either 0.9% NaCl, RO 25-1553 (1 mg·mL⁻¹) or sildenafil (10 mg·mL⁻¹) 60 min prior to tissue harvesting. Data are means+SEMs; * p<0.05 vs. corresponding normoxia group, n = 8 experiments each.