Reactive oxygen species (ROS) formed during acute high altitude exposure contribute to cerebral vascular leak and development of acute mountain sickness (AMS). Nuclear factor (erythroid-derived 2)-related factor 2 (Nrf2) is a transcription factor that regulates expression of greater than 90% of antioxidant genes, but prophylactic treatment with Nrf2 activators has not yet been tested as an AMS therapy. We hypothesized that prophylactic activation of the antioxidant genome with Nrf2 activators would attenuate high-altitude-induced ROS formation and cerebral vascular leak and that some drugs currently used to treat AMS symptoms have an additional trait of Nrf2 activation. Drugs commonly used to treat AMS were screened with a luciferase reporter cell system for their effectiveness to activate Nrf2, as well as being tested for their ability to decrease high altitude cerebral vascular leak in vivo. Compounds that showed favorable results for Nrf2 activation from our screen and attenuated high altitude cerebral vascular leak in vivo were further tested in brain microvascular endothelial cells (BMECs) to determine if they attenuated hypoxia-induced ROS production and monolayer permeability. Of nine drugs tested, with the exception of dexamethasone, only drugs that showed the ability to activate Nrf2 (Protandim, methazolamide, nifedipine, amlodipine, ambrisentan, and sitaxentan) decreased high-altitude-induced cerebral vascular leak in vivo. In vitro, Nrf2 activation in BMECs before 24 h hypoxia exposure attenuated hypoxic-induced hydrogen peroxide production and permeability. Prophylactic Nrf2 activation is effective at reducing brain vascular leak from acute high altitude exposures. Compared to acetazolamide, methazolamide may offer better protection against AMS. Nifedipine, in addition to its known vasodilatory activities in the lung and protection against high altitude pulmonary edema, may provide protection against brain vascular leak as well.

Cell-free hemoglobin (Hb) exposure may be a pathogenic mediator in the development of pulmonary arterial hypertension (PAH), and when combined with chronic hypoxia the potential for exacerbation of PAH and vascular remodeling is likely more pronounced. We hypothesized that Hb may contribute to hypoxia-driven PAH collectively as a prooxidant, inflammatory, and nitric oxide (NO) scavenger. Using programmable micropump technology, we exposed male Sprague-Dawley rats housed under room air or hypoxia to 12 or 30 mg per day Hb for 3, 5, and 7 wk. Blood pressure, cardiac output, right ventricular hypertrophy, and indexes of pulmonary vascular remodeling were evaluated. Additionally, markers of oxidative stress, NO bioavailability and inflammation were determined. Hb increased pulmonary arterial (PA) pressure, pulmonary vessel wall stiffening, and right heart hypertrophy with temporal and dose dependence in both room air and hypoxic cohorts. Hb induced a modest increase in plasma oxidative stress markers (malondialdehyde and 4-hydroxynonenal), no change in NO bioavailability, and increased lung ICAM protein expression. Treatment with the antioxidant Tempol attenuated Hb-induced pulmonary arterial wall thickening, but not PA pressures or ICAM expression. Chronic exposure to low plasma Hb concentrations (range = 3-10 μM) lasting up to 7 wk in rodents induces pulmonary vascular disease via inflammation and to a lesser extent by Hb-mediated oxidation. Tempol demonstrated a modest effect on the attenuation of Hb-induced pulmonary vascular disease. NO bioavailability was found to be of minimal importance in this model.

Hemoglobin-based oxygen carriers (HBOC) have been primarily studied for blood loss treatment. More recently infusions of HBOC in euvolemic subjects have been proposed for a wide variety of potential therapies in which increased tissue oxygenation would be beneficial. However, compared with the exchange transfusion models to study blood loss, less is known about HBOC oxygen delivery and vasoacitvity when it is infused in euvolemic subjects. We hypothesized that HBOC [polymerized bovine hemoglobin (PBvHb)] infusion creating hypervolemia would increase oxygen delivery to tissues during acute global hypoxia. Vascular oxygen content and hemodynamics were determined after euvolemic rats were infused with 3 ml of either lactated Ringer or PBvHb solution (13 g/dl, 1.3 g/kg) during acute hypoxia (FIO 2 = 10%, 4 h) or normoxia (FIO 2 = 21%) exposure. Our data demonstrated that compared with Ringer-infused animals, in hypoxia and normoxia, PBvHb treatment improved oxygen content but raised mean arterial pressure, lowered stroke volume, heart rate, and cardiac index, which resulted in a net reduction in blood flow and oxygen delivery to the tissues. The PBvHb vasoactive effect was similar in magnitude and direction as to the Ringer-infused animals treated with a nitric oxide synthase inhibitor nitro-l-arginine, suggesting the PBvHb effect is mediated via nitric oxide scavenging. We conclude that infusion of PBvHb is not likely to be useful in treating global hypoxia under these conditions.