Measuring hemoglobin oxygen saturation during graded hypoxic hypoxia in rat striatum

A Translational Model of Incomplete Catch-Up Growth: Early-Life Hypoxia and the Effect of Physical Activity

Advances in therapies have led to prolonged survival from many previously lethal health threats in children, notably among prematurely born babies and those with congenital heart disease. Evidence for catch‐up growth is common in these children, but in many cases the adult phenotype is never achieved. A translational animal model is required in which specific tissues can be studied over a reasonable time interval. We investigated the impact of postnatal hypoxia (HY) (12%O₂ (HY12) or 10% O₂ (HY10)) on growth in rats relative to animals raised in room air. Subgroups had access to running wheels following the HY period. Growth was fully compensated in adult HY12 rats but not HY10 rats. The results of this study indicate that neonatal hypoxia can be a useful model for the elucidation of mechanisms that mediate successful catch‐up growth following neonatal insults and identify the critical factors that prevent successful catch‐up growth.

Imaging of brain oxygenation with magnetic resonance imaging: A validation with positron emission tomography in the healthy and tumoural brain

The partial pressure in oxygen remains challenging to map in the brain. Two main strategies exist to obtain surrogate measures of tissue oxygenation: the tissue saturation studied by magnetic resonance imaging (S_tO₂-MRI) and the identification of hypoxia by a positron emission tomography (PET) biomarker with 3-[¹⁸F]fluoro-1-(2-nitro-1-imidazolyl)-2-propanol ([¹⁸F]-FMISO) as the leading radiopharmaceutical. Nonetheless, a formal validation of S_tO₂-MRI against FMISO-PET has not been performed. The objective of our studies was to compare the two approaches in (a) the normal rat brain when the rats were submitted to hypoxemia; (b) animals implanted with four tumour types differentiated by their oxygenation. Rats were submitted to normoxic and hypoxemic conditions. For the brain tumour experiments, U87-MG, U251-MG, 9L and C6 glioma cells were orthotopically inoculated in rats. For both experiments, S_tO₂-MRI and [¹⁸F]-FMISO PET were performed sequentially. Under hypoxemia conditions, S_tO₂-MRI revealed a decrease in oxygen saturation in the brain. Nonetheless, [¹⁸F]-FMISO PET, pimonidazole immunohistochemistry and molecular biology were insensitive to hypoxia. Within the context of tumours, S_tO₂-MRI was able to detect hypoxia in the hypoxic models, mimicking [¹⁸F]-FMISO PET with high sensitivity/specificity. Altogether, our data clearly support that, in brain pathologies, S_tO₂-MRI could be a robust and specific imaging biomarker to assess hypoxia.

Intermittent hypobaric hypoxia induces neuroprotection in kainate-induced oxidative stress in rats

Severe hypoxia induces oxidative stress, which can lead to brain injury. In this study, we wanted to determine whether intermittent hypobaric hypoxia induces oxidative stress in the brain. In adult rats exposed to 380 mmHg in a hypobaric chamber for 3 h/day for 6 days, we determined the levels of malondialdehyde and nitric oxide derivatives in the brain, which indicated that there was no oxidative stress. The levels of N-acetylaspartate indicated that there was no neuronal loss or mitochondrial dysfunction and finally because apoptotic proteins such as caspase-3 and nuclear factor-kappa B (NF-κB) were not activated, apoptosis was probably not induced. The increase in the expression of erythropoietin (EPO) in the brain of rats exposed to hypoxia confirms the efficacy of the method used to induce hypoxia in the brain. Because EPO have antioxidant effects on the brain, the results suggest that intermittent hypoxia can increase the antioxidant capacity of the brain. This effect of intermittent hypoxia was studied using the systemic administration of kainate, as a model of brain oxidative stress. Kainate treatment induces oxidative stress in the brain, which is measured by an increase in lipid peroxidation and nitric oxide. Furthermore, in rats treated with kainate, both caspase-3 and NF-κB activity increased. However, in rats previously exposed to intermittent hypobaric hypoxia, 3 h per day for 6 days, the effect of kainate treatment resulted in the reduction of both oxidative stress and apoptotic activity. This study demonstrates that intermittent hypobaric hypoxia can increase brain antioxidant capacity in rats and induces neuroprotection in kainate-induced oxidative injury.