Severe hypoxia exposure inhibits larval brain development but does not affect the capacity to mount a cortisol stress response in zebrafish

Fish nursery habitats are increasingly hypoxic and the brain is recognized as highly hypoxia-sensitive, yet there is a lack of information on the effects of hypoxia on the development and function of the larval fish brain. Here, we tested the hypothesis that by inhibiting brain development, larval exposure to severe hypoxia has persistent functional effects on the cortisol stress response in zebrafish (Danio rerio). Exposing 5 days post-fertilization (dpf) larvae to 10% dissolved O2 (DO) for 16 h only marginally reduced survival, but it decreased forebrain neural proliferation by 55%, and reduced the expression of neurod1, gfap, and mbpa, markers of determined neurons, glia, and oligodendrocytes, respectively. The 5 dpf hypoxic exposure also elicited transient increases in whole body cortisol and in crf, uts1, and hsd20b2 expression, key regulators of the endocrine stress response. Hypoxia exposure at 5 dpf also inhibited the cortisol stress response to hypoxia in 10 dpf larvae and increased hypoxia tolerance. However, 10% DO exposure at 5 dpf for 16h did not affect the cortisol stress response to a novel stressor in 10 dpf larvae or the cortisol stress response to hypoxia in adult fish. Therefore, while larval exposure to severe hypoxia can inhibit brain development, it also increases hypoxia tolerance. These effects may transiently reduce the impact of hypoxia on the cortisol stress response but not its functional capacity to respond to novel stressors. We conclude that the larval cortisol stress response in zebrafish has a high capacity to cope with severe hypoxia-induced neurogenic impairment.

Colonic Oxygen Microbubbles Augment Systemic Oxygenation and CO2 Removal in a Porcine Smoke Inhalation Model of Severe Hypoxia

Inhalation injury can lead to pulmonary complications resulting in the development of respiratory distress and severe hypoxia. Respiratory distress is one of the major causes of death in critically ill patients with a reported mortality rate of up to 45%. The present study focuses on the effect of oxygen microbubble (OMB) infusion via the colon in a porcine model of smoke inhalation-induced lung injury. Juvenile female Duroc pigs (n=6 colonic OMB, n=6 no treatment) ranging from 39-51 kg in weight were exposed to smoke under general anesthesia for 2 h. Animals developed severe hypoxia 48 h after smoke inhalation as reflected by reduction in SpO2 to 66.3 % +/- 13.1% and PaO2 to 45.3 +/- 7.6 mmHg, as well as bilateral diffuse infiltrates demonstrated on chest x-ray. Colonic OMB infusion (75 - 100 mL/kg dose) resulted in significant improvements in systemic oxygenation as demonstrated by an increase in PaO2 of 13.2 +/- 4.7 mmHg and SpO2 of 15.2% +/- 10.0% out to 2.5 h, compared to no-treatment control animals that experienced a decline in PaO2 of 8.2 +/- 7.9 mmHg and SpO2 of 12.9% +/- 18.7% over the same timeframe. Likewise, colonic OMB decreased PaCO2 and PmvCO2 by 19.7 +/- 7.6 mmHg and 7.6 +/- 6.7 mmHg, respectively, compared to controls that experienced increases in PaCO2 and PmvCO2 of 17.9 +/- 11.7 mmHg and 18.3 +/- 11.2 mmHg. We conclude that colonic OMB therapy has potential to treat patients experiencing severe hypoxemic respiratory failure.

Aerobic scope does matter in the temperature-size rule but only under optimal conditions

We united theoretical predictions of the factors responsible for the evolutionary significance of the temperature-size rule (TSR). We assumed that (i) the TSR is a response to temperature-dependent oxic conditions, (ii) body size decrease is a consequence of cell shrinkage in response to hypoxia, (iii) this response enables organisms to maintain a wide scope for aerobic performance, and (iv) it prevents a decrease in fitness. We examined three clones of the rotifer Lecane inermis exposed to three experimental regimes: mild hypoxia, severe hypoxia driven by a too high temperature, and severe hypoxia driven by an inadequate oxygen concentration. We compared the following traits in normoxia- and hypoxia-exposed rotifers: nuclear size (a proxy for cell size), body size, specific dynamic action (SDA, a proxy of aerobic metabolism) and two fitness measures, the population growth rate and eggs/female ratio. The results showed that (i) under mildly hypoxic conditions, our causative reasoning was correct, except that one of the clones decreased in body size without a decrease in nuclear size, and (ii) in more stressful environments, rotifers exhibited clone- and condition-specific responses, which were equally successful in terms of fitness levels. Our results indicate the importance of the rule testing conditions. The important conclusions were that (i) a body size decrease at higher temperatures enabled the maintenance of a wide aerobic scope under clone-specific, thermally optimal conditions, and (ii) this response was not the only option to prevent fitness reduction under hypoxia.

P.077 Mixed autoimmune hemolytic anemia: an unusual cause of ischemic stroke and extensive cerebral microbleeds

Background: Mixed autoimmune hemolytic anemia (mAIHA) is a rare autoimmune disorder that results in hemolysis with thrombotic complications like ischemic stroke. This is the first case report of cerebral microbleeds secondary to mAIHA. Methods: A literature review of mAIHA and cerebral microbleeds was conducted using the PubMed and Ovid MEDLINE databases from 1980 to 2021. Results: A 76 year old male with congenital deafness and rheumatoid arthritis presented with diffuse livedo reticularis and abdominal pain. He had fulminant hemolysis with new neurologic deficits and altered mental status. CT/CTA of the head and neck were unremarkable. MR brain revealed extensive cerebral microbleeds and multi-territory ischemic strokes. He was diagnosed with mAIHA, started on pulse methylprednisolone, and had no further microbleeds on follow-up MRI. From his clinical picture, common causes of cerebral microbleeds were ruled out such as cerebral amyloid angiopathy and hypertension. The pathogenesis of his microbleeds may be from concomitant severe hypoxia or a prothrombotic state, both previously reported in the literature. Conclusions: This is the first case report of extensive cerebral microbleeds secondary to mAIHA. When a patient develops acute neurologic deficits in the context of mAIHA, extensive cerebral microbleeds may be present possibly due to concomitant severe hypoxia versus a prothrombotic state.

A High Fidelity Transmural Anisotropic Ventricular Tissue Model Function to Investigate the Interaction Mechanisms of Drug: An In-Silico Model for Pharmacotherapy

A high fidelity transmural anisotropic ventricular tissue model consisting of endocardial, mid myocardial, and epicardial myocytes were configured to investigate drug interaction, such as Hydroxychloroquine (HCQ), under hypoxia conditions without and with pro-arrhythmic comorbidity like hypokalemia in (a) ventricular tissue b) its arrhythmogenesis for different dosages and (b) two different pacing sequences (Normal and tachycardiac). In-silico ventricular modeling indicates HCQ has an insignificant effect on hypoxia with and without comorbidities, except in the combination of mild hypoxia with moderate hypokalemia condition and severe hypoxia with mild hypokalemia where it initiated a re-entrant arrhythmia. Secondly, incorporating drug dosage variations indicates the 10 μM HCQ created PVCs for all settings except in severe hypoxia conditions where re-entrant arrhythmia occurred. In addition to the dosage of HCQ utilized for treatment, the pacing protocol also influences the appearance of re-entrant arrhythmia only for severe hypoxia with 10 μM HCQ dosage alone. For all other conditions, including tachycardiac pacing protocol, no arrhythmia occurred. These findings infer that the arrhythmic fatality rate due to HCQ treatment for hypoxia can be effectively alleviated by subtly altering or personalizing the dosage of HCQ and aid in the treatment of hypoxia-induced symptoms caused by COVID.