Neuroprotective Effects of Individual or Combined Exposure to Hypoxia and Hypercapnia in the Experiment

Protective Effects of Obstructive Sleep Apnea on Outcomes After Subarachnoid Hemorrhage: A Nationwide Analysis

BACKGROUND

Obstructive sleep apnea (OSA) is typically associated with an increased risk of cardiovascular and cerebrovascular disease. Recent studies, however, have suggested that hypercapnia and chronic intermittent hypoxia may potentially provide protection against ischemic events like stroke.

OBJECTIVE

To evaluate the impact of OSA with presentation, hospital course, and treatment outcomes of patients with subarachnoid hemorrhage (SAH).

METHODS

Data for patients with SAH between the years 2011 and 2015 were extracted from the Nationwide Inpatient Sample (NIS) and stratified based on diagnosis codes for OSA. Univariate analysis was used to assess the prevalence of comorbidities in OSA patients diagnosed with SAH and several covariates, including patient demographics, aneurysmal treatment, in-hospital morality rate, length of stay, and costs. Multivariate logistic regression models analyzed the relationship between several comorbidities, including OSA, tobacco use, and hypertension, and poor outcomes after SAH.

RESULTS

Data from 49 265 SAH patients were used in this study, of which 2408 (4.9%) also had a concomitant OSA diagnosis. Patients with OSA compared to all other SAH patients had a significantly lower in-hospital mortality rate, as well as statistically significant lower odds of vasospasm, stroke, and poor outcomes. Additionally, hypercholesterolemia, obesity, and tobacco use disorder were also associated with more favorable outcomes.

CONCLUSION

SAH patients with OSA are significantly less likely to have a poor outcome when compared to non-OSA patients, despite having an increased risk of several comorbidities.

The brains of six African mole-rat species show divergent responses to hypoxia

Mole-rats are champions of self-preservation, with increased longevity compared with other rodents their size, strong antioxidant capabilities and specialized defenses against endogenous oxidative stress. However, how the brains of these subterranean mammals handle acute in vivo hypoxia is poorly understood. This study is the first to examine the molecular response to low oxygen in six different species of hypoxia-tolerant mole-rats from sub-Saharan Africa. Protein carbonylation, a known marker of DNA damage (hydroxy-2'-deoxyguanosine), and antioxidant capacity did not change following hypoxia but HIF-1 protein levels increased significantly in the brains of two species. Nearly 30 miRNAs known to play roles in hypoxia tolerance were differentially regulated in a species-specific manner. The miRNAs exhibiting the strongest response to low oxygen stress inhibit apoptosis and regulate neuroinflammation, likely providing neuroprotection. A principal component analysis (PCA) using a subset of the molecular targets assessed herein revealed differences between control and hypoxic groups for two solitary species (Georychus capensis and Bathyergus suillus), which are ecologically adapted to a normoxic environment, suggesting a heightened sensitivity to hypoxia relative to species that may experience hypoxia more regularly in nature. By contrast, all molecular data were included in the PCA to detect a difference between control and hypoxic populations of eusocial Heterocephalus glaber, indicating they may require many lower-fold changes in signaling pathways to adapt to low oxygen settings. Finally, none of the Cryptomys hottentotus subspecies showed a statistical difference between control and hypoxic groups, presumably due to hypoxia tolerance derived from environmental pressures associated with a subterranean and social lifestyle.

Inhibition of miR-135b by SP-1 promotes hypoxia-induced vascular endothelial cell injury via HIF-1α

Myocardial hypoxia-induced endothelial cell apoptosis contributes to cardiac dysfunction, such as myocardial infarction (MI), myocardial ischemia, and heart failure. Thus, it is important to investigate the molecular mechanisms of vascular endothelial cells (VECs) during exposure to hypoxia. SP-1 is an important regulator of cytokines associated with cell functions. We found that SP-1 expression increased in human umbilical vein endothelial cells (HUVECs) exposed to hypoxia by western blot. Then the SP-1 siRNA was transfected into HUVECs under hypoxic condition. MTT assay showed that hypoxia reduced the cell proliferation, but SP-1 siRNA reversed that. Transfection with si-SP-1 also reversed cell apoptosis and reactive oxygen species (ROS) production increased by hypoxia treatment. Moreover, inflammatory phenotype were increased in hypoxia induced HUVECs, including ICAM-1,VCAM-1 levels as well as TNFα, IL-6 and IL-1β secretion, and the si-SP-1 also reversed this effect of hypoxia. Additionally, si-SP-1 increased expression of miR-135b and reduced expression of hypoxia-inducible factor 1-α (HIF-1α), which is the target gene of miR-135b. To investigate the underlying mechanism of SP-1 on hypoxia induced HUVECs injury, the anti-miR-135b or HIF-1α agonist (CoCl2) were used. Finally, the result indicated that both anti-miR-135b or CoCl2 treatment reversed the effects of SP-1 siRNA under hypoxia. In conclusion, the SP-1/miR-135b/HIF-1α axis may play a critical role in hypoxia-induced vascular endothelial injury. Our study thus provides novel insights into the role of this transcription factor and miRNAs in the pathogenesis of hypoxia-induced cardiac dysfunctions.

Proliferative and Synthetic Activity of Nerve Cells after Combined or Individual Exposure to Hypoxia and Hypercapnia

We compared synthetic and proliferative activity of brain cells in rats exposed hypoxia, hypercapnia, or both prior to experimental focal stroke. The mean number of nucleolus organizer regions in penumbra neurons did not change after normobaric hypoxia, but increased after permissive hypercapnia or hypercapnic hypoxia. These data attest to activation of proliferative and synthetic functions in nerve cells, which plays an important role in the neuroprotective mechanisms under conditions of combined exposure to hypoxia and hypercapnia.

Combined exposure to hypercapnia and hypoxia provides its maximum neuroprotective effect during focal ischemic injury in the brain

BACKGROUND

In the present research, we compared the neuroprotective efficiency of combined and isolated exposure to hypoxia and hypercapnia preceding focal cerebral ischemic injury in rats. The study was conducted to verify the hypothesis of a possible increase in normobaric hypoxia (NbH; 90 mm Hg) efficiency when combined with permissive hypercapnia (PH; 50 mm Hg).

METHODS

The rats from the test groups were subjected to a 15-fold exposure to NbH (90 mm Hg) and/or PH (50 mm Hg). After the 15th exposure, cerebral ischemic injury was induced by photochemical thrombosis. Seventy-two hours later, neurologic deficit was determined on the Neurological Severity Score scale and by the rotarod test, and the volume of cerebral infarction was measured after focal photochemical thrombosis.

RESULTS

The neurologic deficit decreased most efficiently in rats that underwent PH and hypercapnic hypoxia (HH) exposure, whereas NbH had no impact on the neurologic status of the animals. On the contrary, motor coordination disturbances were minimal during exposure to hypoxia and HH. All respiratory interventions reduced the cerebral ischemic infarction volume in rats. The smallest infarction volumes were registered in the area of photochemical thrombosis in rats from the hypercapnic-hypoxic impact group, whereas exposure to NbH or PH did not show any cross difference.

CONCLUSIONS

The impact of PH has greater neuroprotective potential compared with NbH. Thus, we can assume that hypercapnia is a predominant factor in providing neuroprotection in combination with hypoxia.