Effect of pre-term birth on oxidative stress responses to normoxic and hypoxic exercise

Antioxidant and neurodevelopmental gene polymorphisms in prematurely born individuals influence hypoxia-related oxidative stress

Preterm born (PTB) infants are at risk for injuries related to oxidative stress. We investigated the association between antioxidant and neurodevelopmental gene polymorphisms and oxidative stress parameters in PTB male young adults and their term-born counterparts at rest and during exercise. Healthy young PTB (N = 22) and full-term (N = 15) males underwent graded exercise tests in normobaric normoxic (FiO2 = 0.21) and hypoxic (FiO2 = 0.13) conditions. CAT rs1001179 was associated with decrease in nitrites in the whole group and in PTB individuals (P = 0.017 and P = 0.043, respectively). GPX1 rs1050450 was associated with decrease in ferric reducing antioxidant power in the whole group and in full-term individuals (P = 0.017 and P = 0.021, respectively). HIF1A rs11549465 was associated with decrease in nitrotyrosine and increase in malondialdehyde (P = 0.022 and P = 0.018, respectively). NOTCH4 rs367398 was associated with increase in advanced oxidation protein products and nitrites (P = 0.002 and P = 0.004, respectively) in hypoxia. In normoxia, NOTCH4 rs367398 was associated with increase in malondialdehyde in the whole group (P = 0.043). BDNF rs6265 was associated with decreased nitrites/nitrates in the whole group and in PTB individuals (P = 0.009 and P = 0.043, respectively). Polymorphisms in investigated genes and PTB might influence oxidative stress response after exercise in normoxic or hypoxic conditions far beyond the neonatal period in young male adults.

Baroreflex sensitivity is blunted in hypoxia independently of changes in inspired carbon dioxide pressure in prematurely born male adults

Premature birth may result in specific cardiovascular responses to hypoxia and hypercapnia, that might hamper high-altitude acclimatization. This study investigated the consequences of premature birth on baroreflex sensitivity (BRS) under hypoxic, hypobaric and hypercapnic conditions. Seventeen preterm born males (gestational age, 29 ± 1 weeks), and 17 age-matched term born adults (40 ± 0 weeks) underwent consecutive 6-min stages breathing different oxygen and carbon dioxide concentrations at both sea-level and high-altitude (3375 m). Continuous blood pressure and ventilatory parameters were recorded in normobaric normoxia (NNx), normobaric normoxic hypercapnia (NNx + CO2 ), hypobaric hypoxia (HHx), hypobaric normoxia (HNx), hypobaric normoxia hypercapnia (HNx + CO2 ), and hypobaric hypoxia with end-tidal CO2 clamped at NNx value (HHx + clamp). BRS was assessed using the sequence method. Across all conditions, BRS was lower in term born compared to preterm (13.0 ± 7.5 vs. 21.2 ± 8.8 ms⋅mmHg-1 , main group effect: p < 0.01) participants. BRS was lower in HHx compared to NNx in term born (10.5 ± 4.9 vs. 16.0 ± 6.0 ms⋅mmHg-1 , p = 0.05), but not in preterm (27.3 ± 15.7 vs. 17.6 ± 8.3 ms⋅mmHg-1 , p = 0.43) participants, leading to a lower BRS in HHx in term born compared to preterm (p < 0.01). In conclusion, this study reports a blunted response of BRS during acute high-altitude exposure without any influence of changes in inspired CO2 in healthy prematurely born adults.

Protective effect of mussel polysaccharide on cyclophosphamide-induced intestinal oxidative stress injury via Nrf2-Keap1 signaling pathway

The hard-shelled mussel (Mytilus coruscus) has been used as a traditional Chinese medicine and health food in China for centuries. Polysaccharides from mussel has been reported to have multiple biological functions, however, it remains unclear whether mussel polysaccharide (MP) exerts protective effects in intestinal functions, and the underlying mechanisms of action remain unclear. The aim of this study was to investigate the protective effects and mechanism of MP on intestinal oxidative injury in mice. In this study, 40 male BALB/C mice were used, with 30 utilized to produce an animal model of intestinal oxidative injury with intraperitoneal injection of cyclophosphamide (Cy) for four consecutive days. The protective effects of two different doses of MP (300 and 600 mg/kg) were assessed by investigating the change in body weight, visceral index, and observing colon histomorphology. Moreover, the underlying molecular mechanisms were investigated by measuring the antioxidant enzymes and related signaling molecules through ELISA, real-time PCR, and western blot methods. The results showed that MP pretreatment effectively protected the intestinal from Cy-induced injury: improved the colon tissue morphology and villus structure, increased superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GSH-Px) activities, and reduced malondialdehyde (MDA) content in serum and colon tissues. Meanwhile, MP also significantly increased the expression levels of SOD, GSH-Px, heme oxygenase-1 (HO-1), and nuclear factor E2-related factor 2 (Nrf2) mRNA in colon tissues. Further, western blot results showed that the expression of Nrf2 protein was significantly upregulated while kelch-like ECH-associated protein 1 (Keap1) was significantly downregulated by MP in the colonic tissues. This study indicates that MP can ameliorate Cy-induced oxidative stress injury in mice, and Nrf2-Keap1 signaling pathway may mediate these protective effects.

Microvascular and oxidative stress responses to acute high-altitude exposure in prematurely born adults

Premature birth is associated with endothelial and mitochondrial dysfunction, and chronic oxidative stress, which might impair the physiological responses to acute altitude exposure. We assessed peripheral and oxidative stress responses to acute high-altitude exposure in preterm adults compared to term born controls. Post-occlusive skeletal muscle microvascular reactivity and oxidative capacity from the muscle oxygen consumption recovery rate constant (k) were determined by Near-Infrared Spectroscopy in the vastus lateralis of seventeen preterm and seventeen term born adults. Measurements were performed at sea-level and within 1 h of arrival at high-altitude (3375 m). Plasma markers of pro/antioxidant balance were assessed in both conditions. Upon acute altitude exposure, compared to sea-level, preterm participants exhibited a lower reperfusion rate (7 ± 31% vs. 30 ± 30%, p = 0.046) at microvascular level, but higher k (6 ± 32% vs. -15 ± 21%, p = 0.039), than their term born peers. The altitude-induced increases in plasma advanced oxidation protein products and catalase were higher (35 ± 61% vs. -13 ± 48% and 67 ± 64% vs. 15 ± 61%, p = 0.034 and p = 0.010, respectively) and in xanthine oxidase were lower (29 ± 82% vs. 159 ± 162%, p = 0.030) in preterm compared to term born adults. In conclusion, the blunted microvascular responsiveness, larger increases in oxidative stress and skeletal muscle oxidative capacity may compromise altitude acclimatization in healthy adults born preterm.

Urine and Fecal 1H-NMR Metabolomes Differ Significantly between Pre-Term and Full-Term Born Physically Fit Healthy Adult Males

Preterm birth (before 37 weeks gestation) accounts for ~10% of births worldwide and remains one of the leading causes of death in children under 5 years of age. Preterm born adults have been consistently shown to be at an increased risk for chronic disorders including cardiovascular, endocrine/metabolic, respiratory, renal, neurologic, and psychiatric disorders that result in increased death risk. Oxidative stress was shown to be an important risk factor for hypertension, metabolic syndrome and lung disease (reduced pulmonary function, long-term obstructive pulmonary disease, respiratory infections, and sleep disturbances). The aim of this study was to explore the differences between preterm and full-term male participants' levels of urine and fecal proton nuclear magnetic resonance (¹H-NMR) metabolomes, during rest and exercise in normoxia and hypoxia and to assess general differences in human gut-microbiomes through metagenomics at the level of taxonomy, diversity, functional genes, enzymatic reactions, metabolic pathways and predicted gut metabolites. Significant differences existed between the two groups based on the analysis of ¹H-NMR urine and fecal metabolomes and their respective metabolic pathways, enabling the elucidation of a complex set of microbiome related metabolic biomarkers, supporting the idea of distinct host-microbiome interactions between the two groups and enabling the efficient classification of samples; however, this could not be directed to specific taxonomic characteristics.

Respiratory responses to hypoxia during rest and exercise in individuals born pre-term: a state-of-the-art review

The pre-term birth survival rate has increased considerably in recent decades, and research investigating the long-term effects of premature birth is growing. Moreover, altitude sojourns are increasing in popularity and are often accompanied by various levels of physical activity. Individuals born pre-term appear to exhibit altered acute ventilatory responses to hypoxia, potentially predisposing them to high-altitude illness. These impairments are likely due to the use of perinatal hyperoxia stunting the maturation of carotid body chemoreceptors, but may also be attributed to limited lung diffusion capacity and/or gas exchange inefficiency. Aerobic exercise capacity also appears to be reduced in this population. This may relate to the aforementioned respiratory impairments, or could be due to physiological limitations in pulmonary blood flow or at the exercising muscle (e.g. mitochondrial efficiency). However, surprisingly, the debilitative effects of exercise when performed at altitude do not seem to be exacerbated by premature birth. In fact, it is reasonable to speculate that pre-term birth could protect against the consequences of exercise combined with hypoxia. The mechanisms that underlie this assertion might relate to differences in oxidative stress responses or in cardiopulmonary morphology in pre-term individuals, compared to their full-term counterparts. Further research is required to elucidate the independent effects of neonatal treatment, sex differences and chronic lung disease, and to establish causality in some of the proposed mechanisms that could underlie the differences discussed throughout this review. A more in-depth understanding of the acclimatisation responses to chronic altitude exposures would also help to inform appropriate interventions in this clinical population.

Effects of Pre-Term Birth on the Cardio-Respiratory Responses to Hypoxic Exercise in Children

Pre-term birth is associated with numerous cardio-respiratory sequelae in children. Whether these impairments impact the responses to exercise in normoxia or hypoxia remains to be established. Fourteen prematurely-born (PREM) (Mean ± SD; gestational age 29 ± 2 weeks; age 9.5 ± 0.3 years), and 15 full-term children (CONT) (gestational age 39 ± 1 weeks; age 9.7 ± 0.9 years), underwent incremental exercise tests to exhaustion in normoxia (FiO₂ = 20.9%) and normobaric hypoxia (FiO₂ = 13.2%) on a cycle ergometer. Cardio-respiratory variables were measured throughout. Peak power output was higher in normoxia than hypoxia (103 ± 17 vs. 77 ± 18 W; p < 0.001), with no difference between CONT and PREM (94 ± 23 vs. 86 ± 19 W; p = 0.154). VO₂peak was higher in normoxia than hypoxia in CONT (50.8 ± 7.2 vs. 43.8 ± 9.9 mL·kg^-1·min^-1; p < 0.001) but not in PREM (48.1 ± 7.5 vs. 45.0 ± 6.8 mL·kg^-1·min^-1; p = 0.137; interaction p = 0.044). Higher peak heart rate (187 ± 11 vs. 180 ± 10 bpm; p = 0.005) and lower stroke volume (72 ± 13 vs. 77 ± 14 mL; p = 0.004) were observed in normoxia versus hypoxia in CONT, with no such differences in PREM (p = 0.218 and >0.999, respectively). In conclusion, premature birth does not appear to exacerbate the negative effect of hypoxia on exercise capacity in children. Further research is warranted to identify whether prematurity elicits a protective effect, and to clarify the potential underlying mechanisms.

Altitude and COVID-19: Friend or foe? A narrative review

Recent reports suggest that high-altitude residence may be beneficial in the novel coronavirus disease (COVID-19) implicating that traveling to high places or using hypoxic conditioning thus could be favorable as well. Physiological high-altitude characteristics and symptoms of altitude illnesses furthermore seem similar to several pathologies associated with COVID-19. As a consequence, high altitude and hypoxia research and related clinical practices are discussed for potential applications in COVID-19 prevention and treatment. We summarize the currently available evidence on the relationship between altitude/hypoxia conditions and COVID-19 epidemiology and pathophysiology. The potential for treatment strategies used for altitude illnesses is evaluated. Symptomatic overlaps in the pathophysiology of COVID-19 induced ARDS and high altitude illnesses (i.e., hypoxemia, dyspnea…) have been reported but are also common to other pathologies (i.e., heart failure, pulmonary embolism, COPD…). Most treatments of altitude illnesses have limited value and may even be detrimental in COVID-19. Some may be efficient, potentially the corticosteroid dexamethasone. Physiological adaptations to altitude/hypoxia can exert diverse effects, depending on the constitution of the target individual and the hypoxic dose. In healthy individuals, they may optimize oxygen supply and increase mitochondrial, antioxidant, and immune system function. It is highly debated if these physiological responses to hypoxia overlap in many instances with SARS-CoV-2 infection and may exert preventive effects under very specific conditions. The temporal overlap of SARS-CoV-2 infection and exposure to altitude/hypoxia may be detrimental. No evidence-based knowledge is presently available on whether and how altitude/hypoxia may prevent, treat or aggravate COVID-19. The reported lower incidence and mortality of COVID-19 in high-altitude places remain to be confirmed. High-altitude illnesses and COVID-19 pathologies exhibit clear pathophysiological differences. While potentially effective as a prophylactic measure, altitude/hypoxia is likely associated with elevated risks for patients with COVID-19. Altogether, the different points discussed in this review are of possibly some relevance for individuals who aim to reach high-altitude areas. However, due to the ever-changing state of understanding of COVID-19, all points discussed in this review may be out of date at the time of its publication.

Cardio-respiratory, oxidative stress and acute mountain sickness responses to normobaric and hypobaric hypoxia in prematurely born adults

PURPOSE

We compared the effects of hypobaric and normobaric hypoxia on select cardio-respiratory responses, oxidative stress and acute mountain sickness (AMS) severity in prematurely born individuals, known to exhibit blunted hypoxic ventilatory response.

METHODS

Sixteen prematurely born but otherwise healthy males underwent two 8-h hypoxic exposures under: (1) hypobaric hypoxic [HH; terrestrial altitude 3840 m; P_iO₂:90.2 (0.5) mmHg; BP: 478 (2) mmHg] and (2) normobaric hypoxic [NH; P_iO₂:90.6 (0.9) mmHg; F_iO₂:0.142 (0.001)] condition. Resting values of capillary oxyhemoglobin saturation (SpO₂), heart rate (HR) and blood pressure were measured before and every 2 h during the exposures. Ventilatory responses and middle cerebral artery blood flow velocity (MCAv) were assessed at rest and during submaximal cycling before and at 4 and 8 h. Plasmatic levels of selected oxidative stress and antioxidant markers and AMS symptoms were also determined at these time points.

RESULTS

HH resulted in significantly lower resting (P = 0.010) and exercise (P = 0.004) SpO₂ as compared to NH with no significant differences in the ventilatory parameters, HR or blood pressure. No significant differences between conditions were found in resting or exercising MCAv and measured oxidative stress markers. Significantly lower values of ferric-reducing antioxidant power (P = 0.037) were observed during HH as opposed to NH. AMS severity was higher at 8 h compared to baseline (P = 0.002) with no significant differences between conditions.

CONCLUSION

These data suggest that, in prematurely born adults, 8-h exposure to hypobaric, as opposed to normobaric hypoxia, provokes greater reductions in systemic oxygenation and antioxidant capacity. Further studies investigating prolonged hypobaric exposures in this population are warranted.

REGISTRATION

NCT02780908 (ClinicalTrials.gov).