Carbonic anhydrase inhibition improves pulmonary artery reactivity and nitric oxide-mediated relaxation in sugen-hypoxia model of pulmonary hypertension

Current Overview of the Biology and Pharmacology in Sugen/Hypoxia-Induced Pulmonary Hypertension in Rats

The Sugen 5416/hypoxia (Su/Hx) rat model of pulmonary arterial hypertension (PAH) demonstrates most of the distinguishing features of PAH in humans, including increased wall thickness and obstruction of the small pulmonary arteries along with plexiform lesion formation. Recently, significant advancement has been made describing the epidemiology, genomics, biochemistry, physiology, and pharmacology in Su/Hx challenge in rats. For example, there are differences in the overall reactivity to Su/Hx challenge in different rat strains and only female rats respond to estrogen treatments. These conditions are also encountered in human subjects with PAH. Also, there is a good translation in both the biochemical and metabolic pathways in the pulmonary vasculature and right heart between Su/Hx rats and humans, particularly during the transition from the adaptive to the nonadaptive phase of right heart failure. Noninvasive techniques such as echocardiography and magnetic resonance imaging have recently been used to evaluate the progression of the pulmonary vascular and cardiac hemodynamics, which are important parameters to monitor the efficacy of drug treatment over time. From a pharmacological perspective, most of the compounds approved clinically for the treatment of PAH are efficacious in Su/Hx rats. Several compounds that show efficacy in Su/Hx rats have advanced into phase II/phase III studies in humans with positive results. Results from these drug trials, if successful, will provide additional treatment options for patients with PAH and will also further validate the excellent translation that currently exists between Su/Hx rats and the human PAH condition.

Effect of 5 weeks of oral acetazolamide on patients with pulmonary vascular disease: A randomized, double-blind, cross-over trial

BACKGROUND

The carbonic anhydrase inhibitor acetazolamide stimulates ventilation through metabolic acidosis mediated by renal bicarbonate excretion. In animal models, acetazolamide attenuates acute hypoxia-induced pulmonary hypertension (PH), but its efficacy in treating patients with PH due to pulmonary vascular disease (PVD) is unknown.

METHODS

28 PVD patients (15 pulmonary arterial hypertension, 13 distal chronic thromboembolic PH), 13 women, mean±SD age 61.6±15.0 years stable on PVD medications, were randomised in a double-blind crossover protocol to 5 weeks acetazolamide (250mg b.i.d) or placebo separated by a ≥2 week washout period. Primary endpoint was the change in 6-minute walk distance (6MWD) at 5 weeks. Additional endpoints included safety, tolerability, WHO functional class, quality of life, arterial blood gases, and hemodynamics (by echocardiography).

RESULTS

Acetazolamide had no effect on 6MWD compared to placebo (treatment effect: mean change [95%CI] -18 [-40 to 4]m, p=0.102) but increased arterial blood oxygenation through hyperventilation induced by metabolic acidosis. Other measures including pulmonary hemodynamics were unchanged. No severe adverse effects occurred, side effects that occurred significantly more frequently with acetazolamide vs. placebo were change in taste (22/0%), paraesthesia (37/4%) and mild dyspnea (26/4%).

CONCLUSIONS

In patients with PVD, acetazolamide did not change 6MWD compared to placebo despite improved blood oxygenation. Some patients reported a tolerable increase in dyspnoea during acetazolamide treatment, related to hyperventilation, induced by the mild drug-induced metabolic acidosis. Our findings do not support the use of acetazolamide to improve exercise in patients with PVD at this dosing.

CLINICALTRIALS

GOV IDENTIFIER

NCT02755298.

A peripheral system disease-Pulmonary hypertension

Pulmonary hypertension (PH) is a cardiovascular disorder characterized by substantial morbidity and mortality rates. It is a chronic condition characterized by intricate pathogenesis and uncontrollable factors. We summarized the pathological effects of estrogen, genetics, neuroinflammation, intestinal microbiota, metabolic reorganization, and histone modification on PH. PH is not only a pulmonary vascular disease, but also a systemic disease. The findings emphasize that the onset of PH is not exclusively confined to the pulmonary vasculature, consequently necessitating treatment approaches that extend beyond targeting pulmonary blood vessels. Hence, the research on the pathological mechanism of PH is not limited to target organs such as pulmonary vessels, but also focuses on exploring other fields (such as estrogen, genetics, neuroinflammation, intestinal microbiota, metabolic reorganization, and histone modification).

Mechanisms of pulmonary vascular dysfunction in pulmonary hypertension and implications for novel therapies

Pulmonary hypertension (PH) is a serious disease characterized by various degrees of pulmonary vasoconstriction and progressive fibroproliferative remodeling and inflammation of the pulmonary arterioles that lead to increased pulmonary vascular resistance, right ventricular hypertrophy, and failure. Pulmonary vascular tone is regulated by a balance between vasoconstrictor and vasodilator mediators, and a shift in this balance to vasoconstriction is an important component of PH pathology, Therefore, the mainstay of current pharmacological therapies centers on pulmonary vasodilation methodologies that either enhance vasodilator mechanisms such as the NO-cGMP and prostacyclin-cAMP pathways and/or inhibit vasoconstrictor mechanisms such as the endothelin-1, cytosolic Ca2+, and Rho-kinase pathways. However, in addition to the increased vascular tone, many patients have a "fixed" component in their disease that involves altered biology of various cells in the pulmonary vascular wall, excessive pulmonary artery remodeling, and perivascular fibrosis and inflammation. Pulmonary arterial smooth muscle cell (PASMC) phenotypic switch from a contractile to a synthetic and proliferative phenotype is an important factor in pulmonary artery remodeling. Although current vasodilator therapies also have some antiproliferative effects on PASMCs, they are not universally successful in halting PH progression and increasing survival. Mild acidification and other novel approaches that aim to reverse the resident pulmonary vascular pathology and structural remodeling and restore a contractile PASMC phenotype could ameliorate vascular remodeling and enhance the responsiveness of PH to vasodilator therapies.