Hypoxia-induced brain cell damage in male albino wistar rat

Neuroglobin Facilitates Neuronal Oxygenation through Tropic Migration under Hypoxia or Anemia in Rat: How Does the Brain Breathe?

The discovery of neuroglobin (Ngb), a brain- or neuron-specific member of the hemoglobin family, has revolutionized our understanding of brain oxygen metabolism. Currently, how Ngb plays such a role remains far from clear. Here, we report a novel mechanism by which Ngb might facilitate neuronal oxygenation upon hypoxia or anemia. We found that Ngb was present in, co-localized to, and co-migrated with mitochondria in the cell body and neurites of neurons. Hypoxia induced a sudden and prominent migration of Ngb towards the cytoplasmic membrane (CM) or cell surface in living neurons, and this was accompanied by the mitochondria. In vivo, hypotonic and anemic hypoxia induced a reversible Ngb migration toward the CM in cerebral cortical neurons in rat brains but did not alter the expression level of Ngb or its cytoplasm/mitochondria ratio. Knock-down of Ngb by RNA interference significantly diminished respiratory succinate dehydrogenase (SDH) and ATPase activity in neuronal N2a cells. Over-expression of Ngb enhanced SDH activity in N2a cells upon hypoxia. Mutation of Ngb at its oxygen-binding site (His64) significantly increased SDH activity and reduced ATPase activity in N2a cells. Taken together, Ngb was physically and functionally linked to mitochondria. In response to an insufficient oxygen supply, Ngb migrated towards the source of oxygen to facilitate neuronal oxygenation. This novel mechanism of neuronal respiration provides new insights into the understanding and treatment of neurological diseases such as stroke and Alzheimer's disease and diseases that cause hypoxia in the brain such as anemia.

Role of hypoxia-inducible factor in postoperative delirium of aged patients: A review

Postoperative delirium is common, especially in older patients. Delirium is associated with prolonged hospitalization, an increased risk of postoperative complications, and significant mortality. The mechanism of postoperative delirium is not yet clear. Cerebral desaturation occurred during the maintenance period of general anesthesia and was one of the independent risk factors for postoperative delirium, especially in the elderly. Hypoxia stimulates the expression of hypoxia-inducible factor-1 (HIF-1), which controls the hypoxic response. HIF-1 may have a protective role in regulating neuron apoptosis in neonatal hypoxia-ischemia brain damage and may promote the repair and rebuilding process in the brain that was damaged by hypoxia and ischemia. HIF-1 has a neuroprotective effect during cerebral hypoxia and controls the hypoxic response by regulating multiple pathways, such as glucose metabolism, angiogenesis, erythropoiesis, and cell survival. On the other hand, anesthetics have been reported to inhibit HIF activity in older patients. So, we speculate that HIF plays an important role in the pathophysiology of postoperative delirium in the elderly. The activity of HIF is reduced by anesthetics, leading to the inhibition of brain protection in a hypoxic state. This review summarizes the possible mechanism of HIF participating in postoperative delirium in elderly patients and provides ideas for finding targets to prevent or treat postoperative delirium in elderly patients.

Hypoxia modeling techniques: A review

Hypoxia is the main cause and effect of a large number of diseases, including the most recent one facing the world, the coronavirus disease (COVID-19). Hypoxia is divided into short-term, long-term, and periodic, it can be the result of diseases, climate change, or living and traveling in the high mountain regions of the world. Since each type of hypoxia can be a cause and a consequence of various physiological changes, the methods for modeling these hypoxias are also different. There are many techniques for modeling hypoxia under experimental conditions. The most common animal for modeling hypoxia is a rat. Hypoxia models (hypoxia simulations) in rats are a tool to study the effect of various conditions on the oxygen supply of the body. These models can provide a necessary information to understand hypoxia and also provide effective treatment, highlighting the importance of various reactions of the body to hypoxia. The main parameters when choosing a model should be reproducibility and the goal that the scientist wants to achieve. Hypoxia in rats can be reproduced both ways exogenously and endogenously. The reason for writing this review was the aim to systematize the models of rats available in the literature in order to facilitate their selection by scientists. The relative strengths and limitations of each model need to be identified and understood in order to evaluate the information obtained from these models and extrapolate these results to humans to develop the necessary generalizations. Despite these problems, animal models have been and remain vital to understanding the mechanisms involved in the development and progression of hypoxia. The eligibility criteria for the selected studies was a comprehensive review of the methods and results obtained from the studies. This made it possible to make generalizations and give recommendations on the application of these methods. The review will assist scientists in choosing an appropriate hypoxia simulation method, as well as assist in interpreting the results obtained with these methods.

Attenuated succinate accumulation relieves neuronal injury induced by hypoxia in neonatal mice

Hypoxia causes neonatal neuronal damage. However, the underlying mechanism remains unclear. This study aimed to explore the changes in succinate levels and identify the mechanisms underlying their contribution to hypoxia-induced damage in newborn mice. The neonatal C57BL/6J mouse hypoxia model was used in our study. We evaluated the levels of succinate, iron, reactive oxygen species (ROS), and mitochondrial ROS, and assessed mitophagy, neuronal damage, and learning and memory function, after hypoxia treatment. The neonatal mice showed increased succinate levels in the early hypoxia stage, followed by increased levels of oxidative stress, iron stress, neuronal damage, and cognitive deficits. Succinate levels were significantly reduced following treatment with inhibitors of succinate dehydrogenase (SDH), purine nucleotide cycle (PNC), and malate/aspartate shuttle (MAS), with the corresponding attenuation of oxidative stress, iron stress, neuronal damage, and cognitive impairment. Reversal catalysis of SDH through fumarate from the PNC and MAS pathways might be involved in hypoxia-induced succinate accumulation. Succinate accumulation in the early period after hypoxia may crucially contribute to oxidative and iron stress. Relieving succinate accumulation at the early hypoxia stage could prevent neuronal damage and cognitive impairment in neonatal hypoxia.

Histopathological, histochemical and biochemical postmortem changes in induced fatal hypothermia in rats

Reaching a postmortem diagnosis of hypothermia is challenging in forensic practice. Therefore, this study was conducted to detect the histopathological, histochemical and biochemical changes that occur in adult albino rats following exposure to induced fatal hypothermia. Twenty-four adult albino rats were divided into the negative control, moderate hypothermia, severe hypothermia and hypoxia groups. Rats in the control group were euthanized when those in the moderate hypothermic group died. Blood samples were collected via heart puncture, and the cerebrum, heart, suprarenal gland, kidney, liver and skeletal muscle were removed to investigate the biochemical, histochemical and histopathological changes. Postmortem assessment depicted significant changes in lipid peroxidation, represented by increased malondialdehyde levels in the studied organs of the rats in hypothermic and hypoxia groups. Histopathological examination of the rats’ organs revealed degeneration and necrosis in the hypothermia and hypoxia groups. Sections taken from the severe hypothermic rats revealed a loss of normal cardiac tissue architecture, necrotic changes in the pyramidal cells in the cerebral cortex, and massive necrosis, mainly in the tubules of the renal cortex and medulla. These findings suggest that histological changes might be used as biochemical markers for postmortem diagnosing of fatal hypothermia, particularly in severe hypothermic conditions.

Key points

Death by hypothermia is a serious public health problem worldwide.

Confirming a diagnosis and determining the cause of death in cases of hypothermia are among the most difficult practices in forensic medicine.

Death by hypothermia might be associated with structural abnormalities in various organs.

Studies using different tissue staining techniques will enable an overall illustration of the role of histopathological changes in body organs as indicators of hypothermia.

Cobalt accumulation and iron-regulatory protein profile expression in immature mouse brain after perinatal exposure to cobalt chloride

Developing brain is very sensitive to the influence of environmental factors during gestation and the neonatal period. The aim of the study is to assess cobalt and iron accumulation in the brain as well as changes in the expression of iron-regulatory proteins transferrin receptor 1, hepcidin, and ferroportin in suckling mice. Perinatal exposure to cobalt chloride increased significantly cobalt content in brain tissue homogenates of 18-day-old (d18) and 25-day-old (d25) mice inducing alterations in brain iron homeostasis. Higher degree of transferrin receptor 1 expression was demonstrated in cobalt chloride-exposed mice with no substantial changes between d18 and d25 mice. A weak ferroportin expression was found in 18-day-old control and cobalt-treated mouse brain. Cobalt exposure of d25 mice resulted in increased ferroportin expression in brain compared to the untreated age-matched control group. Hepcidin level in cobalt-exposed groups was decreased in d18 mice and slightly increased in d25 mice. The obtained data contribute for the better understanding of metal toxicity impact on iron homeostasis in the developing brain with further possible implications in neurodegeneration.

Mesenchymal Stem/Stromal Cell-Mediated Mitochondrial Transfer and the Therapeutic Potential in Treatment of Neurological Diseases

Mesenchymal stem/stromal cells (MSCs) are multipotent stem cells that can be derived from various tissues. Due to their regenerative and immunomodulatory properties, MSCs have been extensively researched and tested for treatment of different diseases/indications. One mechanism that MSCs exert functions is through the transfer of mitochondria, a key player involved in many biological processes in health and disease. Mitochondria transfer is bidirectional and has an impact on both donor and recipient cells. In this review, we discussed how MSC-mediated mitochondrial transfer may affect cellular metabolism, survival, proliferation, and differentiation; how this process influences inflammatory processes; and what is the molecular machinery that mediates mitochondrial transfer. In the end, we summarized recent advances in preclinical research and clinical trials for the treatment of stroke and spinal cord injury, through application of MSCs and/or MSC-derived mitochondria.