Mice and Rats Display Different Ventilatory, Hematological, and Metabolic Features of Acclimatization to Hypoxia

Pneumonectomy combined with SU5416 or monocrotaline pyrrole does not cause severe pulmonary hypertension in mice

In the field of pulmonary hypertension (PH), a well-established protocol to induce severe angioproliferation in rats (SuHx) involves combining the VEGF-R inhibitor Sugen 5416 (SU5416) with 3 wk of hypoxia (Hx). In addition, injecting monocrotaline (MCT) into rats can induce inflammation and shear stress in the pulmonary vasculature, leading to neointima-like remodeling. However, the SuHx protocol in mice is still controversial, with some studies suggesting it yields higher and reversible PH than Hx alone, possibly due to species-dependent hypoxic responses. To establish an alternative rodent model of PH, we hypothesized mice would be more sensitive to hemodynamic changes secondary to shear stress compared with Hx. We attempted to induce severe and irreversible PH in mice by combining SU5416 or monocrotaline pyrrole (MCTP) injection with pneumonectomy (PNx). However, our experiments showed SU5416 administered to mice at various time points after PNx did not result in severe PH. Similarly, mice injected with MCTP after PNx (MPNx) showed no difference in right ventricular systolic pressure or exacerbated pulmonary vascular remodeling compared with PNx alone. These findings collectively demonstrate that C57/B6 mice do not develop severe and persistent PH when PNx is combined with either SU5416 or MCTP.NEW & NOTEWORTHY We attempted to establish a mouse model of severe and irreversible pulmonary hypertension by substituting hypoxia with pulmonary overcirculation. To do so, we treated mice with either SU5416 or monocrotaline pyrrole after pneumonectomy and performed hemodynamic evaluations for PH. Despite this "two-hit" protocol, mice did not exhibit signs of severe pulmonary hypertension or exacerbated pulmonary vascular remodeling compared with PNx alone.

The respiratory health effects of acute in vivo diesel and biodiesel exhaust in a mouse model

BACKGROUND

Biodiesel, a renewable diesel fuel that can be created from almost any natural fat or oil, is promoted as a greener and healthier alternative to commercial mineral diesel without the supporting experimental data to back these claims. The aim of this research was to assess the health effects of acute exposure to two types of biodiesel exhaust, or mineral diesel exhaust or air as a control in mice. Male BALB/c mice were exposed for 2-hrs to diluted exhaust obtained from a diesel engine running on mineral diesel, Tallow biodiesel or Canola biodiesel. A room air exposure group was used as a control. Twenty-four hours after exposure, a variety of respiratory related end point measurements were assessed, including lung function, responsiveness to methacholine and airway and systemic immune responses.

RESULTS

Tallow biodiesel exhaust exposure resulted in the greatest number of significant effects compared to Air controls, including increased airway hyperresponsiveness (178.1 ± 31.3% increase from saline for Tallow biodiesel exhaust exposed mice compared to 155.8 ± 19.1 for Air control), increased airway inflammation (63463 ± 13497 cells/mL in the bronchoalveolar lavage of Tallow biodiesel exhaust exposed mice compared to 40561 ± 11800 for Air exposed controls) and indications of immune dysregulation. In contrast, exposure to Canola biodiesel exhaust resulted in fewer significant effects compared to Air controls with a slight increase in airway resistance at functional residual capacity and indications of immune dysregulation. Exposure to mineral diesel exhaust resulted in significant effects between that of the two biodiesels with increased airway hyperresponsiveness and indications of immune dysregulation.

CONCLUSION

These data show that a single, brief exposure to biodiesel exhaust can result in negative health impacts in a mouse model, and that the biological effects of exposure change depending on the feedstock used to make the biodiesel.

Low Atmospheric Oxygen Attenuates Alpha Oscillations in the Primary Motor Cortex of Awake Rats

Oxygen is pivotal for survival of animals. Their cellular activity and cognitive behavior are impaired when atmospheric oxygen is insufficient, called hypoxia. However, concurrent effects of hypoxia on physiological signals are poorly understood. To address this question, we simultaneously recorded local field potentials in the primary motor cortex, primary somatosensory, and anterior cingulate cortex, electrocardiograms, electroolfactograms, and electromyograms of rats under acute hypoxic conditions (i.e., 5.0% O2). Exposure to acute hypoxia significantly attenuated alpha oscillations alone in the primary motor cortex, while we failed to find any effects of acute hypoxia on the oscillatory power in the somatosensory cortex or anterior cingulate cortex. These area- and frequency-specific effects by hypoxia may be accounted for by neural innervation from the brainstem to each cortical area via thalamic relay nuclei. Moreover, we found that heart rate and respiratory rate were increased during acute hypoxia and high heart rate was maintained even after the oxygen level returned to the baseline. Altogether, our study characterizes a systemic effect of atmospheric hypoxia on neural and peripheral signals from physiological viewpoints, leading to bridging a gap between cellular and behavioral levels.

KCNK3 channel is important for the ventilatory response to hypoxia in rats

To clarify the contribution of KCNK3/TASK-1 channel chemoreflex in response to hypoxia and hypercapnia, we used a unique Kcnk3-deficient rat. We assessed ventilatory variables using plethysmography in Kcnk3-deficient and wild-type rats at rest in response to hypoxia (10% O2) and hypercapnia (4% CO2). Immunostaining for C-Fos, a marker of neuronal activity, was performed to identify the regions of the respiratory neuronal network involved in the observed response.Under basal conditions, we observed increased minute ventilation in Kcnk3-deficient rats, which was associated with increased c-Fos positive cells in the ventrolateral region of the medulla oblongata. Kcnk3-deficient rats show an increase in ventilatory response to hypoxia without changes in response to hypercapnia. In Kcnk3-deficient rats, linked to an increased hypoxia response, we observed a greater increase in c-Fos-positive cells in the first central relay of peripheral chemoreceptors and Raphe Obscurus. This study reports that KCNK3/TASK-1 deficiency in rats induces an inadequate peripheral chemoreflex, alternating respiratory rhythmogenesis, and hypoxic chemoreflex.

The glutamatergic drive to breathe is reduced in severe but not moderate hypoxia in Damaraland mole-rats

Damaraland mole-rats (Fukomys damarensis) are a hypoxia-tolerant fossorial species that exhibit a robust hypoxic metabolic response (HMR) and blunted hypoxic ventilatory response (HVR). Whereas the HVR of most adult mammals is mediated by increased excitatory glutamatergic signalling, naked mole-rats, which are closely related to Damaraland mole-rats, do not utilize this pathway. Given their phylogenetic relationship and similar lifestyles, we hypothesized that the signalling mechanisms underlying physiological responses to acute hypoxia in Damaraland mole-rats are like those of naked mole-rats. To test this, we used pharmacological antagonists of glutamatergic α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPARs) and N-methyl-d-aspartate receptors (NMDARs), combined with plethysmography, respirometry and thermal RFID chips, to non-invasively evaluate the role of excitatory AMPAR and NMDAR signalling in mediating ventilatory, metabolic and thermoregulatory responses, respectively, to 1 h of 5 or 7% O2. We found that AMPAR or NMDAR antagonism have minimal impacts on the HMR or hypoxia-mediated changes in thermoregulation. Conversely, the 'blunted' HVR of Damaraland mole-rats is reduced by either AMPAR or NMDAR antagonism such that the onset of the HVR occurs in less severe hypoxia. In more severe hypoxia, antagonists have no impact, suggesting that these receptors are already inhibited. Together, these findings indicate that the glutamatergic drive to breathe decreases in Damaraland mole-rats exposed to severe hypoxia. These findings differ from other adult mammals, in which the glutamatergic drive to breathe increases with hypoxia.

Comparison of the toxicological potential of two JUUL ENDS products to reference cigarette 3R4F and filtered air in a 90-day nose-only inhalation toxicity study

Electronic nicotine delivery systems (ENDS) are generally recognized as less harmful alternatives for those who would otherwise continue to smoke cigarettes. The potential toxicity of aerosols generated from JUUL Device and Virginia Tobacco (VT3) or Menthol (ME3) JUULpods at 3.0% nicotine concentration was assessed in rats exposed at target aerosol concentrations of 1400 μg/L for up to 6 h/day on a 5 day/week basis for at least 90 days (general accordance with OECD 413). 3R4F reference cigarette smoke (250 μg/L) and Filtered Air were used as comparators. JUUL ENDS product aerosol exposures at >5x the 3R4F cigarette smoke level resulted in greater plasma nicotine and cotinine levels (up to 2x). Notable cigarette smoke related effects included pronounced body weight reductions in male rats, pulmonary inflammation evidenced by elevated lactate dehydrogenase, pro-inflammatory cytokines and neutrophils in bronchoalveolar lavage fluid, increased heart and lung weights, and minimal to marked respiratory tract histopathology. In contrast, ENDS aerosol exposed animals had minimal body weight changes, no measurable inflammatory changes and minimal to mild laryngeal squamous metaplasia. Despite the higher exposure levels, VT3 and ME3 did not result in significant toxicity or appreciable respiratory histopathology relative to 3R4F cigarette smoke following 90 days administration.

High Altitude Pulmonary Edema, High Altitude Cerebral Edema, and Acute Mountain Sickness: an enhanced opinion from the High Andes - La Paz, Bolivia 3,500 m

Traveling to high altitudes for entertainment or work is sometimes associated with acute high altitude pathologies. In the past, scientific literature from the lowlander point of view was primarily based on mountain climbing. Sea level scientists developed all guidelines, but they need modifications for medical care in high altitude cities. Acute Mountain Sickness, High Altitude Pulmonary Edema, and High Altitude Cerebral Edema are medical conditions that some travelers can face. We present how to diagnose and treat acute high altitude pathologies, based on 51 years of high altitude physiology research and medical practice in hypobaric hypoxic diseases in La Paz, Bolivia (3,600 m; 11,811 ft), at the High Altitude Pulmonary and Pathology Institute (HAPPI - IPPA). These can occasionally present after flights to high altitude cities, both in lowlanders or high-altitude residents during re-entry. Acute high altitude ascent diseases can be adequately diagnosed and treated in high altitude cities following the presented guidelines. Treating these high-altitude illnesses, we had no loss of life. Traveling to a high altitude with sound medical advice should not be feared as it has many benefits. Nowadays, altitude descent and evacuation are not mandatory in populated highland cities, with adequate medical resources.

The Brain at High Altitude: From Molecular Signaling to Cognitive Performance

The brain requires over one-fifth of the total body oxygen demand for normal functioning. At high altitude (HA), the lower atmospheric oxygen pressure inevitably challenges the brain, affecting voluntary spatial attention, cognitive processing, and attention speed after short-term, long-term, or lifespan exposure. Molecular responses to HA are controlled mainly by hypoxia-inducible factors. This review aims to summarize the cellular, metabolic, and functional alterations in the brain at HA with a focus on the role of hypoxia-inducible factors in controlling the hypoxic ventilatory response, neuronal survival, metabolism, neurogenesis, synaptogenesis, and plasticity.

Cucumeropsis mannii seed oil protects against Bisphenol A-induced testicular mitochondrial damages

There has been increasing search for the ameliorative properties of seed oils against toxicants. bisphenol A acts as an estrogenic endocrine-disrupting chemical capable of causing male infertility. This study aimed to explore Cucumeropsis mannii seed oil effects against mitochondrial damage in rats using bisphenol A. Forty-eight rats were randomly assigned to six groups (n = 6) of eight rats each and fed the same food and water for 6 weeks. The group A rats were given 1 mL olive oil, while the ones in group B were given bisphenol A at 100 mL/kg body weight via oral route. Group C received C. mannii seed oil 7.5 mL/kg body weight C. mannii seed oil, while group D, group E, and group F were pre-administered bisphenol A at 100 mL/kg body weight, followed by treatment with C. mannii seed oil at 7.5, 5, and 2.5 mL/kg body weight, respectively. Antioxidant enzymes, glutathione, reactive oxygen species, testicular volume, malondialdehyde, body weight, and testicular studies were done using standard methods. The results of the bisphenol A-administered group showed a significant decrease in the antioxidant enzymes, glutathione, body weight, and testicular volume with elevation in the levels of reactive oxygen species, malondialdehyde, and testicular indices. BPA + CMSO-treated group showed a significant increase in GPx activity compared with BPA-exposed rats. CMSO treatment significantly increased catalase activity in comparison with that of rats exposed to BPA. Remarkably, C. mannii seed oil and bisphenol A co-administration significantly reversed the abnormalities observed in the dysregulated biochemical biomarkers. Our findings suggest that C. mannii seed oil has considerable antioxidant potential which can be explored in therapeutic development against systemic toxicity induced by exposure to bisphenol A. Cucumeropsis mannii seed oil protects against bisphenol A-induced testicular mitochondria damages.

Hypoxia extends lifespan and neurological function in a mouse model of aging

There is widespread interest in identifying interventions that extend healthy lifespan. Chronic continuous hypoxia delays the onset of replicative senescence in cultured cells and extends lifespan in yeast, nematodes, and fruit flies. Here, we asked whether chronic continuous hypoxia is beneficial in mammalian aging. We utilized the Ercc1 Δ/- mouse model of accelerated aging given that these mice are born developmentally normal but exhibit anatomic, physiological, and biochemical features of aging across multiple organs. Importantly, they exhibit a shortened lifespan that is extended by dietary restriction, the most potent aging intervention across many organisms. We report that chronic continuous 11% oxygen commenced at 4 weeks of age extends lifespan by 50% and delays the onset of neurological debility in Ercc1 Δ/- mice. Chronic continuous hypoxia did not impact food intake and did not significantly affect markers of DNA damage or senescence, suggesting that hypoxia did not simply alleviate the proximal effects of the Ercc1 mutation, but rather acted downstream via unknown mechanisms. To the best of our knowledge, this is the first study to demonstrate that "oxygen restriction" can extend lifespan in a mammalian model of aging.

The relationship between hypoxia exposure and circulating cortisol levels in social and solitary African mole-rats: An initial report

Hypoxemia from exposure to intermittent and/or acute environmental hypoxia (lower oxygen concentration) is a severe stressor for many animal species. The response to hypoxia of the hypothalamic-pituitary-adrenal axis (HPA-axis), which culminates in the release of glucocorticoids, has been well-studied in hypoxia-intolerant surface-dwelling mammals. Several group-living (social) subterranean species, including most African mole-rats, are hypoxia-tolerant, likely due to regular exposure to intermittent hypoxia in their underground burrows. Conversely, solitary mole-rat species, lack many adaptive mechanisms, making them less hypoxia-tolerant than the social genera. To date, the release of glucocorticoids in response to hypoxia has not been measured in hypoxia-tolerant mammalian species. Consequently, this study exposed three social African mole-rat species and two solitary mole-rat species to normoxia, or acute hypoxia and then measured their respective plasma glucocorticoid (cortisol) concentrations. Social mole-rats had lower plasma cortisol concentrations under normoxia than the solitary genera. Furthermore, individuals of all three of the social mole-rat species exhibited significantly increased plasma cortisol concentrations after hypoxia, similar to those of hypoxia-intolerant surface-dwelling species. By contrast, individuals of the two solitary species had a reduced plasma cortisol response to acute hypoxia, possibly due to increased plasma cortisol under normoxia. If placed in perspective with other closely related surface-dwelling species, the regular exposure of the social African mole-rats to hypoxia may have reduced the basal levels of the components for the adaptive mechanisms associated with hypoxia exposure, including circulating cortisol levels. Similarly, the influence of body mass on plasma cortisol levels cannot be ignored. This study demonstrates that both hypoxia-tolerant rodents and hypoxia-intolerant terrestrial laboratory-bred rodents may possess similar HPA-axis responses from exposure to hypoxia. Further research is required to confirm the results from this pilot study and to further confirm how the cortisol concentrations may influence responses to hypoxia in African mole-rat.

Quantifying the effects of anesthesia on intracellular oxygen via low-cost portable microscopy using dual-emissive nanoparticles

Intracellular oxygenation is an important parameter for numerous biological studies. While there are a variety of methods available for acquiring in vivo measurements of oxygenation in animal models, most are dependent on indirect oxygen measurements, restraints, or anesthetization. A portable microscope system using a Raspberry Pi computer and Pi Camera was developed for attaching to murine dorsal window chambers. Dual-emissive boron nanoparticles were used as an oxygen-sensing probe while mice were imaged in awake and anesthetized states. The portable microscope system avoids altered in vivo measurements due to anesthesia or restraints while enabling increased continual acquisition durations.

Oxygen therapy limiting peripheral oxygen saturation to 89-93% is associated with a better survival prognosis for critically ill COVID-19 patients at high altitudes

Patients admitted to the Intensive Care Unit (ICU) with acute hypoxemic respiratory failure automatically receive oxygen therapy to improve inspiratory oxygen fraction (FiO₂). Supplemental oxygen is the most prescribed drug for critically ill patients regardless of altitude of residence. In high altitude dwellers (i.e. in La Paz [≈3,400 m] and El Alto [≈4,150 m] in Bolivia), a peripheral oxygen saturation (SatpO₂) of 89-95% and an arterial partial pressure of oxygen (PaO₂) of 50-67 mmHg (lower as altitude rises), are considered normal values ​​for arterial blood. Consequently, it has been suggested that limiting oxygen therapy to maintain SatpO₂ around normoxia may help avoid episodes of hypoxemia, hyperoxemia, intermittent hypoxemia, and ultimately, mortality. In this study, we evaluated the impact of oxygen therapy on the mortality of critically ill COVID-19 patients who permanently live at high altitudes. A multicenter cross-sectional descriptive observational study was performed on 100 patients admitted to the ICU at the "Clinica Los Andes" (in La Paz city) and "Agramont" and "Del Norte" Hospitals (in El Alto city). Our results show that: 1) as expected, fatal cases were detected only in patients who required intubation and connection to invasive mechanical ventilation as a last resort to overcome their life-threatening desaturation; 2) among intubated patients, prolonged periods in normoxia are associated with survival, prolonged periods in hypoxemia are associated with death, and time spent in hyperoxemia shows no association with survival or mortality; 3) the oxygenation limits required to effectively support the intubated patients' survival in the ICU are between 89% and 93%; 4) among intubated patients with similar periods of normoxemic oxygenation, those with better SOFA scores survive; and 5) a lower frequency of observable reoxygenation events is not associated with survival. In conclusion, our findings indicate that high-altitude patients entering an ICU at altitudes of 3,400 - 4,150 m should undergo oxygen therapy to maintain oxygenation levels between 89 and 93 %.

Adrenergic control of the cardiovascular system in deer mice native to high altitude

Studies of animals native to high altitude can provide valuable insight into physiological mechanisms and evolution of performance in challenging environments. We investigated how mechanisms controlling cardiovascular function may have evolved in deer mice (Peromyscus maniculatus) native to high altitude. High-altitude deer mice and low-altitude white-footed mice (P. leucopus) were bred in captivity at sea level, and first-generation lab progeny were raised to adulthood and acclimated to normoxia or hypoxia. We then used pharmacological agents to examine the capacity for adrenergic receptor stimulation to modulate heart rate (f_H) and mean arterial pressure (P_mean) in anaesthetized mice, and used cardiac pressure-volume catheters to evaluate the contractility of the left ventricle. We found that highlanders had a consistently greater capacity to increase f_H via pharmacological stimulation of β₁-adrenergic receptors than lowlanders. Also, whereas hypoxia acclimation reduced the capacity for increasing P_mean in response to α-adrenergic stimulation in lowlanders, highlanders exhibited no plasticity in this capacity. These differences in highlanders may help augment cardiac output during locomotion or cold stress, and may preserve their capacity for α-mediated vasoconstriction to more effectively redistribute blood flow to active tissues. Highlanders did not exhibit any differences in some measures of cardiac contractility (maximum pressure derivative, dP/dt_max, or end-systolic elastance, E_es), but ejection fraction was highest in highlanders after hypoxia acclimation. Overall, our results suggest that evolved changes in sensitivity to adrenergic stimulation of cardiovascular function may help deer mice cope with the cold and hypoxic conditions at high altitude.

•

High-altitude deer mice have evolved increased aerobic capacity in hypoxia.

•

Cardiovascular regulation was examined in normoxia and chronic hypoxia.

•

Highland mice had increased capacity for β₁-adrenergic stimulation of heart rate.

•

Hypoxia reduced vascular α-adrenergic sensitivity in lowland but not highland mice.

•

Cardiac ejection fraction was elevated in highland mice in chronic hypoxia.

Alzheimer's Disease, Sleep Disordered Breathing, and Microglia: Puzzling out a Common Link

Sleep Disordered Breathing (SDB) and Alzheimer's Disease (AD) are strongly associated clinically, but it is unknown if they are mechanistically associated. Here, we review data covering both the cellular and molecular responses in SDB and AD with an emphasis on the overlapping neuroimmune responses in both diseases. We extensively discuss the use of animal models of both diseases and their relative utilities in modeling human disease. Data presented here from mice exposed to intermittent hypoxia indicate that microglia become more activated following exposure to hypoxia. This also supports the idea that intermittent hypoxia can activate the neuroimmune system in a manner like that seen in AD. Finally, we highlight similarities in the cellular and neuroimmune responses between SDB and AD and propose that these similarities may lead to a pathological synergy between SDB and AD.