The Potential Benefits of the Influenza Vaccination on COVID-19 Mortality Rate-A Retrospective Analysis of Patients in Poland.

In this study,we used publicly available data from the Centrum e-Zdrowia (CeZ) Polish Databank proposing a possible correlation between influenza vaccination and mortality due to COVID-19. We limited our search to the patients with positive COVID­19 laboratory tests from 1 January 2020 to 31 March 2021 and who filled a prescription for any influenza vaccine during the 2019-2020 influenza season. In total, we included 116,277 patients and used a generalized linear model to analyze the data.We found out that patients aged 60+ who received an influenza vaccination have a lower probability of death caused by COVID-19 in comparison to unvaccinated, and the magnitude of this difference grows with age. For people below 60 years old, we did not observe an influence of the vaccination. Our results suggest a potential protective effect of the influenza vaccine on COVID-19 mortality of the elderly. Administration of the influenza vaccine before the influenza season would reduce the burden of increased influenza incidence, the risk of influenza and COVID­19 coinfection and render the essential medical resources accessible to cope with another wave of COVID-19. To our knowledge, this is the first study showing a correlation between influenza vaccination and the COVID-19 mortality rate in Poland.

Effects of mGluR5 positive and negative allosteric modulators on brain damage evoked by hypoxia-ischemia in neonatal rats.

In the present study, we examined the effects of negative and positive allosteric modulators of metabotropic glutamate receptor 5 (mGluR5), fenobam and ADX47273, respectively, on brain damage induced by hypoxia-ischemia (H-I) in 7-day-old rats. The test drugs were administered intraperitoneally 10 min after H-I. Rectal body temperature was measured for 2.5 h after the insult. The number of apoptotic neurons in the immature rat brain was evaluated after 24 h. The wet weight of both hemispheres was determined 14 days after H-I, and its loss was used as an indicator of brain damage. In the vehicle-treated groups, H-I reduced the weight of the ipsilateral (ischemic) hemisphere by approximately 33% and sixfold increased the number of apoptotic cells in the cortex. Fenobam (10 mg/kg) and ADX47273 (5, 10, and 30 mg/kg) had no significant effect on brain damage, although application of fenobam at this dose significantly reduced the number of apoptotic cells. In contrast, fenobam (20 mg/kg) potentiated ischemic brain damage to 57.4% and had no effect on H-I-induced apoptosis. In all of the experimental groups, we detected no significant changes in the weight of the contralateral (control) hemisphere or the rectal temperature. In conclusion, in 7-day-old rats, the bidirectional modulation of mGluR5 by fenobam (10 mg/kg) and ADX47273 (all doses tested) did not result in significant changes in H-I-evoked brain damage, supporting our previous data indicating that also the antagonists of mGluR5 MPEP and MTEP, which reduce neuronal lesions in adult animals submitted to brain ischemia, were ineffective in 7-day-old rat pups.

Delayed preconditioning with NMDA receptor antagonists in a rat model of perinatal asphyxia.

INTRODUCTION: In vitro experiments have demonstrated that preconditioning primary neuronal cultures by temporary application of NMDA receptor antagonists induces long-term tolerance against lethal insults. In the present study we tested whether similar effects also occur in brain submitted to ischemia in vivo and whether the potential benefit outweighs the danger of enhancing the constitutive apoptosis in the developing brain. MATERIAL AND METHODS: Memantine in pharmacologically relevant doses of 5 mg/kg or (+)MK-801 (3 mg/kg) was administered i.p. 24, 48, 72 and 96 h before 3-min global forebrain ischemia in adult Mongolian gerbils or prior to hypoxia/ischemia in 7-day-old rats. Neuronal loss in the hippocampal CA1 in gerbils or weight deficit of the ischemic hemispheres in the rat pups was evaluated after 14 days. Also, the number of apoptotic neurons in the immature rat brain was evaluated. RESULTS: In gerbils only the application of (+)MK-801 24 h before ischemia resulted in significant prevention of the loss of pyramidal neurons. In rat pups administration of (+)MK-801 at all studied times before hypoxia-ischemia, or pretreatment with memantine or with hypoxia taken as a positive control 48 to 92 h before the insult, significantly reduced brain damage. Both NMDA receptor antagonists equally reduced the number of apoptotic neurons after hypoxia-ischemia, while (+)MK-801-evoked potentiation of constitutive apoptosis greatly exceeded the effect of memantine. CONCLUSIONS: We ascribe neuroprotection induced in the immature rats by the pretreatment with both NMDA receptor antagonists 48 to 92 h before hypoxia-ischemia to tolerance evoked by preconditioning, while the neuroprotective effect of (+)MK-801 applied 24 h before the insults may be attributed to direct consequences of the inhibition of NMDA receptors. This is the first report demonstrating the phenomenon of inducing tolerance against hypoxia-ischemia in vivo in developing rat brain by preconditioning with NMDA receptor antagonists.

Hypobaric hypoxia postconditioning reduces brain damage and improves antioxidative defense in the model of birth asphyxia in 7-day-old rats.

Perinatal brain insult mostly resulting from hypoxia-ischemia (H-I) often brings lifelong permanent disability, which has a major impact on the life of individuals and their families. The lack of progress in clinically-applicable neuroprotective strategies for birth asphyxia has led to an increasing interest in alternative methods of therapy, including induction of brain tolerance by pre- and particularly postconditioning. Hypoxic postconditioning represents a promising strategy for preventing ischemic brain damage. The aim of this study was to investigate the potential neuroprotective effect of hypobaric hypoxia (HH) postconditioning applied to 7-day old rats after H-I insult. The mild hypobaric conditions (0.47 atm) used in this study imitate an altitude of 5,000 m. We show that application of mild hypobaric hypoxia at relatively short time intervals (1-6 h) after H-I, repeated for two following days leads to significant neuroprotection, manifested by a reduction in weight loss of the ipsilateral hemisphere observed 14 days after H-I. HH postconditioning results in decrease in reactive oxygen species level observed in all experimental groups. The increase in superoxide dismutase activity observed after H-I is additionally enhanced by HH postconditioning applied 1 h after H-I. The increase observed 3 and 6 h after H-I was not statistically significant. Postconditioning with HH suppresses the glutathione concentration decrease evoked by H-I and increased glutathione peroxidase activity and this effect is not dependent on the time of postconditioning initiation. HH postconditioning had no effect on catalase activity. We show for the first time that HH postconditioning reduces brain damage resulting from H-I in immature rats and that the mechanism potentially involved in this effect is related to antioxidant defense mechanisms of immature brain.

NMDA receptor antagonists MK-801 and memantine induce tolerance to oxygen and glucose deprivation in primary cultures of rat cerebellar granule cells.

Preconditioning is an experimental strategy for reducing ischemic brain damage. There are reports that brief exposure of neurons to NMDA-receptor antagonists may be an adequate preconditioning stressor. We studied effects of preconditioning of the cerebellar granule cells (CGC) in primary culture by 30-minute exposure to NMDA receptor antagonists 0.5 µM MK-801 or 5 µM memantine. CGC were challenged with oxygen and glucose deprivation (OGD) or excitotoxic glutamate and cell viability was tested 24 h later using calcein/ethidium homodimer-1 staining. We studied glutamate-induced increases in 45Ca uptake and in the intracellular Ca2+ level assessed with the fluorescent probe fluo-3. The number of living cells in OGD-treated cultures decreased by 42%. Preconditioning with MK-801 or memantine 24 h earlier reduced cell death to 8% and 30% and 48 h earlier to 27% and 33%, respectively. Pretreatment with MK-801 followed by the standard MK-801 wash out was slightly cytoprotective in a glutamate excitotoxicity test performed immediately; the protection increased significantly 24 h after preconditioning. In both cases the extensive wash out of MK-801 after preconditioning resulted in loss of cytoprotection. The increase in the intracellular Ca2+ level evoked by glutamate was decreased 24 h after preconditioning and even halved in the neuronal cultures 48 h after preconditioning with MK-801 and memantine. Glutamate-induced 45Ca uptake in these cells was decreased by 18%, irrespective of the time laps after preconditioning. These results demonstrate that preconditioning of CGC with NMDA receptor antagonists induces prolonged tolerance to OGD, which is accompanied by the reduction of glutamate-evoked calcium fluxes. The causal relationship between these effects may be suggested.

Changes in the expression of insulin-like growth factor 1 variants in the postnatal brain development and in neonatal hypoxia-ischaemia.

Insulin-like growth factor-1 (IGF-1) is a multifunctional peptide of which numerous isoforms exist. The predominant form, IGF-1Ea is involved in physiological processes while IGF-1Ec (mechano-growth factor, MGF) is expressed in response to a different set of stimuli. We have identified specific changes in the expression patterns of these IGF-1 variants in brain development in normal rats and following neonatal hypoxia-ischaemia (HI). Both IGF-1Ea and IGF-1Ec are expressed during normal postnatal brain development, albeit with highly specific temporal distributions. In contrast, HI produced increased and prolonged expression of the IGF-1Ec isoform only. Importantly, hypoxia alone stimulated the expression of IGF-1Ec as well. Thus, IGF-1Ec may play a role in HI pathology. Neonatal hypoxia-ischaemia occurs in approximately 1:4000-1:10,000 newborns and causes neurological deficits in approximately 75% of those affected. Unfortunately, no specific treatment is available. IGF-1 is known to have neuroprotective activity and its IGF-1Ec variant appears to be an endogenous protective factor in hypoxia-ischaemia. Therefore, IGF-1Ec could potentially be developed into a therapeutic modality for the attenuation or prevention of neuronal damage in this and related disorders.

Neuroprotection by co-treatment and post-treating with calcitriol following the ischemic and excitotoxic insult in vivo and in vitro.

Several in vivo and in vitro studies have demonstrated the neuroprotective potential of pretreatment with 1alpha,25-dihydroxyvitamin D3 (calcitriol). The aim of the present study was to determine the effectiveness of calcitriol administered in vivo after a brain ischemic episode in the rat model of perinatal asphyxia, or when co-applied with or without delay during 24-h exposure of mouse hippocampal, neocortical and cerebellar neuronal cultures to glutamate on their 7th and 12th day in vitro (7 DIV and 12 DIV, respectively). Calcitriol was also administered after acute exposure of rat cerebellar neurons to glutamate. In 7-day-old rat pups subjected to hypoxia-ischemia, acute application of calcitriol in a single dose of 2 microg/kg, 30 min after termination of the insult, or subchronic, 7-day post-treatment with calcitriol, effectively reduced brain damage. The level of neuroprotection exceeded that achieved by hypoxic preconditioning used as the reference neuroprotective method. The results of in vitro experiments revealed the ability of calcitriol to reduce excitotoxicity in a manner dependent on the origin of the neuronal cells, their stage of maturation in culture and the duration of exposure to the excitotoxic insult before calcitriol application. Calcitriol was neuroprotective when it was administered together with glutamate or even after a delay of up to 6h during 24-h excitotoxic challenge of hippocampal and neocortical, but not cerebellar neuronal cultures. Application of calcitriol to cultured cerebellar granule neurons after acute exposure to glutamate was ineffective. In 12 DIV hippocampal cell cultures, 50 nM calcitriol inhibited glutamate-induced caspase-3 activity, while only 100 nM concentrations were effective in 7 DIV cultures. We ascribe the protective effects of calcitriol to the rapid modulation of mechanisms that are instrumental in the direct anti-apoptotic, neuroprotective action of this compound.

CDP-choline (citicoline) attenuates brain damage in a rat model of birth asphyxia.

To estimate protective potential of citicoline in a model of birth asphyxia, the drug was given to 7-day old rats subjected to permanent unilateral carotid artery occlusion and exposed for 65 min to a hypoxic gas mixture. Daily citicoline doses of 100 or 300 m/kg, or vehicle, were injected intraperitoneally for 7 consecutive days beginning immediately after the end of the ischemic-hypoxic insult, and brain damage was assessed by gross zorphology score and weight deficit two weeks after the insult. Caspase-3, alpha-fodrin, Bcl-2, and Hsp70 levels were assessed at 0, 1, and 24 h after the end of the hypoxic insult in another group of rat pups subjected to the same insult and given a single dose of 300 m/kg of citicoline or the vehicle. Citicoline markedly reduced caspase-3 activation and Hsp70 expression 24 h after the insult, and dose-dependently attenuated brain damage. In the context of the well-known excellent safety profile of citicoline, these data suggest that clinical evaluation of the efficacy of the drug in human birth asphyxia may be warranted.

Neuroprotective potential of group I metabotropic glutamate receptor antagonists in two ischemic models.

The neuroprotective potential of mGluR1 and mGluR5 antagonists (group I), EMQMCM and MTEP, respectively was studied using the 3 min forebrain ischemia model in Mongolian gerbils and the hypoxia-ischemia model in 7-day-old rats. Hypoxia-ischemia was induced by unilateral carotid occlusion followed by 75 min exposure to hypoxia (7.3% O(2) in N(2)), forebrain ischemia in gerbils was evoked by bilateral common carotid artery occlusion. The postischemic rectal body temperature in rat pups or brain temperature of gerbils was measured. The drugs were administered i.p. three times every 2 h after the insult, each time in equal doses of 1.25, 2.5 or 5.0 mg/kg. After 2 weeks brain damage was evaluated as weight decrease of the ipsilateral hemisphere in the rat pups or damage to CA1 pyramids in the gerbil hippocampus. The results demonstrated a dose dependent neuroprotection in both ischemic models by EMQMCM, while MTEP was neuroprotective only in the gerbil model of forebrain ischemia. EMQMCM reduced postischemic hyperthermia in gerbils. Thus, the antagonists of mGluR1 and mGluR5 show differential neuroprotective ability in two models of brain ischemia. Postischemic hypothermia may be partially involved in the mechanism of neuroprotection following EMQMCM in gerbils.

Neuroprotective effects of the agonist of metabotropic glutamate receptors ABHxD-I in two animal models of cerebral ischaemia.

The neuroprotective efficacy of 2-aminobicyclo[2.1.1]hexane-2,5-dicarboxylic acid-I (ABHxD-I), a rigid agonist of metabotropic glutamate receptors, was studied using a 3-min global cerebral ischaemia model in Mongolian gerbils and the hypoxia/ischaemia model in 7-day-old rats. The effects on brain damage of ABHxD-I (30 mg/kg, intraperitoneally or 7.5 microg intracerebroventricularly) administered 30 min before global ischaemia or 30 min after hypoxia/ischaemia was evaluated 14 days after the insults. Treatment of adult gerbils with ABHxD-I injected i.c.v. but not systemically, prevented post-ischaemic hyperthermia and substantially reduced brain damage. These effects may reflect low permeability of the adult blood-brain barrier to ABHxD-I, and the role of reduced body and brain temperature in neuroprotection after its i.c.v. administration. ABHxD-I given either i.p. or i.c.v. to developing rats reduced brain damage by 55 and 37%, respectively, without affecting the body temperature. Due to immaturity and increased post-ischaemic permeability of the blood-brain barrier in developing rats, ABHxD-I may induce neuroprotection by direct interference with brain metabotropic glutamate receptors.

Neonatal cerebral hypoxia-ischemia: involvement of FAK-dependent pathway.

Focal adhesion kinase (FAK) is a non-receptor tyrosine kinase thought to play a major role in transducing extracellular matrix (ECM)-derived survival signals into cells. Thus, modulation of FAK activity may affect the linkage between ECM and signaling cascade to which it is connected and may participate in a variety of pathological settings. In the present study, we investigated the effect of neonatal cerebral hypoxia-ischemia (HI) on levels and tyrosine phosphorylation of focal adhesion kinase and the interaction of this enzyme with Src protein tyrosine kinase and adapter protein p130Cas, involved in FAK-mediated signaling pathway. The total amount of focal adhesion kinase as well as its phosphorylated form declined substantially to about 50% of the control between 24 and 48 h after the insult. Concomitantly a decreased association of FAK with its investigated molecular partners, Src kinase and p130Cas protein has been observed. This early response to brain hypoxia-ischemia was attenuated during prolonged recovery with almost complete return to control values at 7 days. These data are indicative of an involvement of FAK-dependent signaling pathway in the evolution of HI-induced neuronal degeneration.

Dantrolene inhibits NMDA-induced 45Ca uptake in cultured cerebellar granule neurons.

Dantrolene is an inhibitor of a skeletal muscle subtype of ryanodine receptors that stabilizes intracellular calcium concentrations and exerts neuroprotective effects in neurons submitted to excitotoxic challenges. The mechanisms of dantrolene-induced neuroprotection are not clear. In this study, using a model of cultured rat cerebellar granule neurons, we demonstrated that dantrolene inhibits NMDA-evoked 45Ca uptake, indicating that this drug may inhibit the activity of NMDA receptor channels. Primary neuronal cultures were incubated for 10 min in Mg(2+)-free ionic medium with NMDA and 45Ca in the presence of different concentrations of dantrolene, then radioactivity in neurons was measured by liquid scintillation spectroscopy. The results demonstrated that dantrolene, applied at micromolar concentrations, inhibits NMDA-evoked 45Ca uptake in neurons in a dose-dependent manner. DMSO, a vehicle to dantrolene, in concentrations used in this study had no effect on NMDA-evoked 45Ca uptake. These results, indicating that dantrolene inhibits activation of the NMDA receptors, might at least partially explain the mechanisms of a dantrolene-evoked protection of neurons against excitotoxicity mediated by agonists of NMDA receptors.

Proinflammatory cytokines in injured rat brain following perinatal asphyxia.

In contrast to astrogliosis, which is common to injuries of the adult CNS, in the developing brain this process is minimal. Reasons postulated for this include the relative immaturity of the immune system and the consequent insufficient production of cytokines to evoke astrogliosis. To explore this hypothesis, the study was undertaken to detect the presence of some proinflammatory cytokines in the injured rat brain following perinatal asphyxia (ischaemia/hypoxia). The localisation of TNF-alpha, IL-15, IL-17 and IL-17 receptors was visualised by means of immunohistochemistry. In numerous neurones of the rat brain, the IL-17 appeared to be constitutively expressed. In the early period of inflammation the IL-15 was produced mainly by the blood cells penetrating the injured brain but later it was synthesised also by reactive astrocytes surrounding brain cysts and forming dense astrogliosis around necrotic brain regions. The direct effect on astrogliosis of other estimated cytokines seems to be negligible. All the results lead to the conclusion that from all cytokines identified in the injured immature rat brain the IL-15 plays the most important role during inflammatory response and participates in the gliosis of reactive astrocytes.