Cardiac oxidative stress and antioxidant status in response to radiation and monocrotaline induced cardiac dysfunction

Cardiovascular disease is the leading cause of death and disability worldwide. Oxidative stress has been implicated in many types of cardiovascular disease. Chronic cardiac stress conditions have been shown to be associated with an increase in myocardial oxidative stress following myocardial infarction, which in turn may lead to depressed contractile function, myocardial remodeling and heart failure. Antioxidants play a protective role against oxidative stress damage through the removal of free radical intermediates and inhibition of oxidation reactions. An imbalance of free radicals and antioxidants results in cellular and sub-cellular damage. Therefore, treatment with non-enzymatic antioxidants may provide protection against high levels of free radicals. We investigated, in three different studies, if treatment with antioxidants can protect the heart under conditions of oxidative stress. In the first study, a complex dietary supplement composed of numerous antioxidants and anti-inflammatory components was given to C57BL/6 mice that received a whole body radiation dose of 5 Gy to investigate potential cardioprotective effects by measuring cardiac antioxidant status and apoptosis. In the second study, the same complex dietary supplement was given to Thy1-GFP mice that received a radiation dose of 10 Gy to the head to investigate the abscopal effect on the heart by measuring cardiac inflammation and fibrosis. In the final study, the potential cardioprotective effects of secoisolariciresinol diglucoside, a compound found in flaxseed, was investigated in a Wistar rat model of pulmonary arterial hypertension by correlating cardiac functions with oxidative stress. We have shown that treatment with antioxidants may offer some protection to the heart in these models of oxidative stress though it is important to consider the extent of oxidative stress and when developing a antioxidant treatment protocol

Diurnal Immune Cell Migration Patterns Characterized in the Spaceflight Environment

Daily diurnal immune rhythm shapes biological pathways of organisms and closely aligns with optimizing energy usage in response to environmental light-dark cycles. Immune mobilization depends on diurnal signals to regulate immunity. In spaceflight, disrupted circadian rhythms and immune systems are noted. However, crosstalk between these systems has not been fully characterized. To fill this knowledge gap, we utilized a ground-based model of spaceflight to phenotype diurnal immunity in mice. For this, 24-week-old male and female mice were exposed to a combination of single-housed, acute 15cGy 5-ion GCRsim irradiation and continuous hindlimb unloading for 2 weeks on a light:dark [12hr:12hr] cycle throughout. Blood was collected at 24 hours and 2 weeks post irradiation and flow cytometrically profiled. Additionally, ribo-depleted, bulk RNA sequencing characterized unique, diurnal and sex-specific biosignatures. This work expands our understanding of diurnal immunity which is important to consider for personalized medicine directives for astronauts. This work was supported in part by the NASA Human Research Program (HRP) Human Factors Behavioral Performance Element Grant 18 18FLAG 2 0028 to AER and Embry-Riddle Start-up grant to Dr. Amber Paul

The effect of secoisolariciresinol diglucoside on oxidative stress and inflammation in cardiac iron overload

Chronic cardiac iron overload directly correlates with cardiac dysfunction and may ultimately cause heart failure. Although recent studies have suggested that altered calcium homeostasis and increased reactive oxygen species (ROS) play roles in iron overload-induced cardiac dysfunction, the exact mechanism(s) of oxidative stressmediated cardiac inflammation, matrix remodelling and cell death remain unclear. Here we examined iron-induced cardiac damage in terms of oxidative stress, inflammation and apoptosis in an in vitro model of cardiac iron overload using the H9c2 cardiac cells. We also investigated the effect of secoisolariciresinol diglucoside (SDG), a component of flaxseed, on the above mentioned parameters. H9c2 cells were treated with 50 μM iron and a pre-treatment of 500 μM SDG was performed by dissolving SDG into serum- and antibiotic-free Dulbecco's Modified Eagle's Medium and for each treatment type, cells were incubated for 24 hours. Cardiac iron overload resulted in increased intracellular ROS while SDG treatment prevented this increase, as measured by the H2DCFDA assay using flow cytometry. Increased gene expression of inflammatory mediators Tumor Necrosis Factor (TNF)-α, interleukin (IL)-10 and interferon (IFN)γ, as well as matrix metalloproteinases (MMP)-2 and 9, and antioxidants glutathione reductase (GSR), superoxide dismutase (SOD)-2 and peroxiredoxin (Prdx)-6 and a decrease in SOD concentration correlated with increased apoptosis as measured by active caspase 3/7 activity and increase in FOXO3. SDG attenuated the increase of gene expression of inflammatory and apoptosis mediators as well as the increase of caspase 3/7 activity caused by iron treatment. SDG also lead to an increase in gene expression of antioxidants GSR, SOD-2 and Prdx-6 when compared to iron treatment. Cardiac iron overload also resulted in an increase in protein levels of p70S6K1 and a decrease in the AMPK levels. The increase of p70S6 and decrease in AMPK levels was prevented by SDG. Pretreatment with SDG attenuated the iron-induced increases in oxidative stress, inflammation and apoptosis, suggesting a cardio-protective role for SDG against cardiac iron overload

The Role of Radiation Induced Injury on Lung Cancer

This manuscript evaluates the role of cell killing, tissue disorganization, and tissue damage on the induction of lung cancer following low dose rate radiation exposures from internally deposited radioactive materials. Beagle dogs were exposed by inhalation to 90Y, 91Y, 144Ce, or 90Sr in fused clay particles. Dogs lived out their life span with complete pathology conducted at the time of death. The radiation dose per cell turnover was characterized and related to the cause of death for each animal. Large doses per cell turnover resulted in acute death from lung damage with extensive cell killing, tissue disorganization, chronic inflammatory disease, fibrosis, and pneumonitis. Dogs with lower doses per cell turnover developed a very high frequency of lung cancer. As the dose per cell turnover was further decreased, no marked tissue damage and no significant change in either life span or lung cancer frequency was observed. Radiation induced tissue damage and chronic inflammatory disease results in high cancer frequencies in the lung. At doses where a high frequency of chromosome damage and mutations would be predicted to occur there was no decrease in life span or increase in lung cancer. Such research suggests that cell killing and tissue damage and the physiological responses to that damage are important mechanisms in radiation induced lung cancer

Secoisolariciresinol diglucoside abrogates oxidative stress-induced damage in cardiac iron overload condition.

Cardiac iron overload is directly associated with cardiac dysfunction and can ultimately lead to heart failure. This study examined the effect of secoisolariciresinol diglucoside (SDG), a component of flaxseed, on iron overload induced cardiac damage by evaluating oxidative stress, inflammation and apoptosis in H9c2 cardiomyocytes. Cells were incubated with 50 μ5M iron for 24 hours and/or a 24 hour pre-treatment of 500 μ M SDG. Cardiac iron overload resulted in increased oxidative stress and gene expression of the inflammatory mediators tumor necrosis factor-α, interleukin-10 and interferon γ, as well as matrix metalloproteinases-2 and -9. Increased apoptosis was evident by increased active caspase 3/7 activity and increased protein expression of Forkhead box O3a, caspase 3 and Bax. Cardiac iron overload also resulted in increased protein expression of p70S6 Kinase 1 and decreased expression of AMP-activated protein kinase. Pre-treatment with SDG abrogated the iron-induced increases in oxidative stress, inflammation and apoptosis, as well as the increased p70S6 Kinase 1 and decreased AMP-activated protein kinase expression. The decrease in superoxide dismutase activity by iron treatment was prevented by pre-treatment with SDG in the presence of iron. Based on these findings we conclude that SDG was cytoprotective in an in vitro model of iron overload induced redox-inflammatory damage, suggesting a novel potential role for SDG in cardiac iron overload

Mitochondria-Targeted Human Catalase in the Mouse Longevity MCAT Model Mitigates Head-Tilt Bedrest-Induced Neuro-Inflammation in the Hippocampus

Microgravity (modeled by head-tilt bedrest and hind-limb unloading), experienced during prolonged spaceflight, results in neurological consequences, central nervous system (CNS) dysfunction, and potentially impairment during the performance of critical tasks. Similar pathologies are observed in bedrest, sedentary lifestyle, and muscle disuse on Earth. In our previous study, we saw that head-tilt bedrest together with social isolation upregulated the milieu of pro-inflammatory cytokines in the hippocampus and plasma. These changes were mitigated in a MCAT mouse model overexpressing human catalase in the mitochondria, pointing out the importance of ROS signaling in this stress response. Here, we used a head-tilt model in socially housed mice to tease out the effects of head-tilt bedrest without isolation. In order to find the underlying molecular mechanisms that provoked the cytokine response, we measured CD68, an indicator of microglial activation in the hippocampus, as well as changes in normal in-cage behavior. We hypothesized that hindlimb unloading (HU) will elicit microglial hippocampal activations, which will be mitigated in the MCAT ROS-quenching mice model. Indeed, we saw an elevation of the activated microglia CD68 marker following HU in the hippocampus, and this pathology was mitigated in MCAT mice. Additionally, we identified cytokines in the hippocampus, which had significant positive correlations with CD68 and negative correlations with exploratory behaviors, indicating a link between neuroinflammation and behavioral consequences. Unveiling a correlation between molecular and behavioral changes could reveal a biomarker indicative of these responses and could also result in a potential target for the treatment and prevention of cognitive changes following long space missions and/or muscle disuse on Earth

Secoisolariciresinol diglucoside attenuates cardiac hypertrophy and oxidative stress in monocrotaline-induced right heart dysfunction

Pulmonary arterial hypertension (PAH) occurs when remodeling of pulmonary vessels leads to increased pulmonary vascular resistance resulting in increased pulmonary arterial pressure. Increased pulmonary arterial pressure results in right ventricle hypertrophy and eventually heart failure. Oxidative stress has been implicated in the pathogenesis of PAH and may play a role in the regulation of cellular signaling involved in cardiac response to pressure overload. Secoisolariciresinol diglucoside (SDG), a component from flaxseed, has been shown to reduce cardiac oxidative stress in various pathophysiological conditions. We investigated the potential protective effects of SDG in a monocrotaline-induced model of PAH. Five- to six-week-old male Wistar rats were given a single intraperitoneal injection of monocrotaline (60 mg/kg) and sacrificed 21 days later where heart, lung, and plasma were collected. SDG (25 mg/kg) was given via gavage as either a 21-day co-treatment or pre-treatment of 14 days before monocrotaline administration and continued for 21 days. Monocrotaline led to right ventricle hypertrophy, increased lipid peroxidation, and elevated plasma levels of alanine transaminase (ALT) and aspartate transaminase (AST). Co-treatment with SDG did not attenuate hypertrophy or ALT and AST levels but decreased reactive oxygen species (ROS) levels and catalase and superoxide dismutase activity compared to the monocrotaline-treated group. Pre-treatment with SDG decreased right ventricle hypertrophy, ROS levels, lipid peroxidation, catalase, superoxide dismutase, and glutathione peroxidase activity and plasma levels of ALT and AST when compared to the monocrotaline group. These findings indicate that pre-treatment with SDG provided better protection than co-treatment in this model of right heart dysfunction, suggesting an important role for SDG in PAH and right ventricular remodeling