Promising effects of xanthine oxidase inhibition by allopurinol on autonomic heart regulation estimated by heart rate variability (HRV) analysis in rats exposed to hypoxia and hyperoxia

Redox mechanisms in autoimmune thyroid eye disease

Thyroid eye disease (TED) is an autoimmune condition affecting the orbit and the eye with its adnexa, often occurring as an extrathyroidal complication of Graves' disease (GD). Orbital inflammatory infiltration and the stimulation of orbital fibroblasts, triggering de novo adipogenesis, an overproduction of hyaluronan, myofibroblast differentiation, and eventual tissue fibrosis are hallmarks of the disease. Notably, several redox signaling pathways have been shown to intensify inflammation and to promote adipogenesis, myofibroblast differentiation, and fibrogenesis by upregulating potent cytokines, such as interleukin (IL)-1β, IL-6, and transforming growth factor (TGF)-β. While existing treatment options can manage symptoms and potentially halt disease progression, they come with drawbacks such as relapses, side effects, and chronic adverse effects on the optic nerve. Currently, several studies shed light on the pathogenetic contributions of emerging factors within immunological cascades and chronic oxidative stress. This review article provides an overview on the latest advancements in understanding the pathophysiology of TED, with a special focus of the interplay between oxidative stress, immunological mechanisms and environmental factors. Furthermore, cutting-edge therapeutic approaches targeting redox mechanisms will be presented and discussed.

Transcutaneous vagus nerve stimulation ameliorates cardiac abnormalities in chronically stressed rats

Chronically stressed patients often have low vagal tone and increased levels of proinflammatory cytokines, which increase their risk for developing cardiac dysfunction. Transcutaneous vagus nerve stimulation (taVNS) is a way to activate the parasympathetic system, which has the ability to reduce inflammation and antagonize excessive sympathetic responses. However, the effectiveness of taVNS in treating cardiac dysfunction caused by chronic unpredictable stress (CUS) has not been studied. To investigate this, we first validated a rat model of CUS, in which the rats were exposed to random stressors daily for 8 weeks. Post CUS, the rats were treated with taVNS (1.0 ms, 6 V, 6 Hz, for 40 min × 2 weeks, alternatively) and their cardiac function and cholinergic flow were evaluated. Furthermore, serum cardiac troponin I (cTnI), cardiac caspase-3, inducible nitric oxide synthase (iNOS), and transforming growth factor (TGF)-β1 expression in rats were also assessed. The chronically stressed rats showed depressed behavior with increased levels of serum corticosterone and proinflammatory cytokines. Electrocardiogram (ECG) and heart rate variability (HRV) studies revealed elevated heart rate, diminished vagal tone, and altered sinus rhythm in CUS rats. Furthermore, the CUS rats demonstrated cardiac hypertrophy and fibrosis with increased caspase-3, iNOS, and TGF-β expression in their myocardium and increased levels of serum cTnI. Interestingly, alternate taVNS therapy for 2 weeks, post CUS, helped alleviate these cardiac abnormalities. These suggest that taVNS could be a useful adjunctive and non-pharmacological approach for managing CUS induced cardiac dysfunction.

Comparative metabolomics analysis reveals high-altitude adaptations in a toad-headed viviparous lizard, Phrynocephalus vlangalii

Extreme environmental conditions at high altitude, such as hypobaric hypoxia, low temperature, and strong UV radiation, pose a great challenge to the survival of animals. Although the mechanisms of adaptation to high-altitude environments have attracted much attention for native plateau species, the underlying metabolic regulation remains unclear. Here, we used a multi-platform metabolomic analysis to compare metabolic profiles of liver between high- and low-altitude populations of toad-headed lizards, Phrynocephalus vlangalii, from the Qinghai-Tibet Plateau. A total of 191 differential metabolites were identified, consisting of 108 up-regulated and 83 down-regulated metabolites in high-altitude lizards as compared with values for low-altitude lizards. Pathway analysis revealed that the significantly different metabolites were associated with carbohydrate metabolism, amino acid metabolism, purine metabolism, and glycerolipid metabolism. Most intermediary metabolites of glycolysis and the tricarboxylic acid cycle were not significantly altered between the two altitudes, but most free fatty acids as well as β-hydroxybutyric acid were significantly lower in the high-altitude population. This may suggest that high-altitude lizards rely more on carbohydrates as their main energy fuel rather than lipids. Higher levels of phospholipids occurred in the liver of high-altitude populations, suggesting that membrane lipids may undergo adaptive remodeling in response to low-temperature stress at high altitude. In summary, this study demonstrates that metabolic profiles differ substantially between high- and low-altitude lizard populations, and that these differential metabolites and metabolic pathways can provide new insights to reveal mechanisms of adaptation to extreme environments at high altitude.

Hydrotrope assisted green synthesis of dicoumarols and in silico and in vitro antibacterial, antioxidant and xanthine oxidase inhibition studies

Aqueous hydrotrope has been employed for the first time to synthesize heteroaryl dicoumarols by condensation of 4-hydroxycoumarin and different heterocyclic aldehydes. This method is highly efficient and green, and the same aqueous hydrotropic solution can be used up to five times without any considerable loss of yield in the product. The synthesized compounds showed good antibacterial potential against Gram-positive (Staphylococcus aureus/NTCC 0997 and B. oceanisediminis) and Gram-negative (Escherichia coli/D0157:H7 and E. coli rosetta) bacterial strains using the Resazurin microtiter plate visual method. The MIC value of 312 µg/ml for compounds 3b, 3k and 3l for S. aureus while 39 µg/ml for compounds 3a, 3b and 3k for E. coli and 625 µg/ml for 3a and 3b for B. oceanisediminis was observed. The compounds were screened via computational methods like molecular docking studies and molecular dynamic simulations with PDB Id's 2W9S and 2EX6. Antioxidant activity was assessed using DPPH and H2O2 assays. Five compounds with the best binding score in molecular docking with XO (PDB ID: 1FIQ) have been tested in an in-vitro study using an enzyme inhibition assay. Novel compound 3b gave the IC50 value of 0.28 µg/ml, comparable to the standard drug Allopurinol.Communicated by Ramaswamy H. Sarma.

Heart rate variability in male rats

The cardiovascular system is primarily controlled by the autonomic nervous system, and any changes in sympathetic or parasympathetic activity also have an impact on myocardial activity. Heart rate variability (HRV) is a readily available metric used to assess heart rate control by the autonomic nervous system. HRV can provide information about neural (parasympathetic, sympathetic, reflex) and humoral (hormones, thermoregulation) control of myocardial activity. Because there are no relevant reference values for HRV parameters in rats in the scientific literature, all experimental results are only interpreted on the basis of changes from currently measured control or baseline HRV values, which are, however, significantly different in individual studies. Considering the significant variability of published HRV data, the present study focused primarily on comparing control or baseline HRV values under different conditions in in vivo experiments involving rats. The aim of the study was therefore to assess whether there are differences in the starting values before the experiment itself.

Effects of partial replacement of dietary flour meal with seaweed polysaccharides on the resistance to ammonia stress in the intestine of hybrid snakehead (Channa maculatus ♀ × Channa argus ♂)

The purpose of this study was to evaluate the effects of partial replacement of dietary flour meal with seaweed polysaccharides on survival rate, histology, intestinal oxidative stress levels, and expression of immune-related genes in hybrid snakeheads under acute ammonia stress. Four experimental diets were set: (C) basal diet with 0% of seaweed polysaccharides as the control group, (MR) basal diet with 10% of seaweed polysaccharides, (HR) basal diet with 15% of seaweed polysaccharides, (HF) basal diet with 10% of fish oil. After 60 days of feeding, fish fed with the diet of C group were sampled as the control group, and other fish were exposed to ammonia nitrogen for 48 h. Two concentrations of total ammonia nitrogen (TAN) were used in this study: 120 mg/L TAN (low concentration exposure group), and 1200 mg/L TAN (high concentration exposure group). After exposure to ammonia nitrogen for 48 h, fish were sampled. The results indicated that adding seaweed polysaccharides to the diet could improve the survival rate of hybrid snakeheads under high concentration of ammonia stress. Histopathological analysis demonstrated multiple abnormalities in gills and intestines after exposure to two concentrations of TAN. The activities of superoxide dismutase (SOD), catalase (CAT), glutathione (GSH), and lactate dehydrogenase (LDH) were all increased in the MR group under two concentrations of TAN stress. The mRNA abundance of immune-related genes in fish intestinal tissues was significantly induced or inhibited. These results suggested that partial replacement of dietary flour meal with seaweed polysaccharides improved the ability of hybrid snakeheads to resist ammonia stress.

The influence of early-life and adulthood stressors on brain neuropeptide-S system

Central administered neuropeptide-S (NPS) was shown to reduce stress response in rodents. This study aimed to investigate the alterations in NPS system upon chronic exposure to early-life and adulthood stressors. Newborn pups underwent maternal separation (MS) from postnatal day 1 to 14 comprised of daily 3-h separations. In the adulthood, 90-min of restraint stress was loaded to males as an acute stress (AS) model. For chronic homotypic stress (CHS), same stressor was applied for 5 consecutive days. The changes in the expression and the release of NPS were monitored by immunohistochemistry and microdialysis, respectively. Throughout the CHS, heart rate variability (HRV) was analyzed on a daily basis. The immunoreactivity for NPS receptor (NPSR) was detected in basolateral amygdala (BLA) and hypothalamic paraventricular nucleus (PVN) by immunofluorescence staining. The NPS expression in the brainstem was increased upon AS which was more prominent following CHS, whereas these responses were found to be blunted in MS counterparts. Similar to histological data, the stress-induced release of NPS in BLA was attenuated in MS rats. CHS-induced elevations in sympatho-vagal balance were alleviated in control rats; which was not observed in MS rats. The expression of NPSR in BLA and PVN was down-regulated in MS rats. The brain NPS/NPSR system appears to be susceptible to the early-life stressors and the subsequent chronic stress exposure in adulthood which results in altered autonomic outflow.

The Role of Oxidative Stress and Therapeutic Potential of Antioxidants in Graves' Ophthalmopathy

Graves’ ophthalmopathy (GO) is the most common extrathyroidal manifestation of Graves’ disease. It is characterized initially by an inflammatory process, followed by tissue remodeling and fibrosis, leading to proptosis, exposure keratopathy, ocular motility limitation, and compressive optic neuropathy. The pathogenic mechanism is complex and multifactorial. Accumulating evidence suggests the involvement of oxidative stress in the pathogenesis of GO. Cigarette smoking, a major risk factor for GO, has been shown to induce reactive oxygen species (ROS) generation and oxidative damage in GO orbital fibroblasts. In addition, an elevation in ROS and antioxidant enzymes is observed in tears, blood, and urine, as well as orbital fibroadipose tissues and fibroblasts from GO patients. In vitro and in vivo studies have examined the efficacy of various antioxidant supplements for GO. These findings suggest a therapeutic role of antioxidants in GO patients. This review summarizes the current understanding of oxidative stress in the pathogenesis and potential antioxidants for the treatment of GO.

Positive Relationship Between Precompetitive Sympathetic Predominance and Competitive Performance in Elite Extreme Sports Athletes

Elite athletes achieve superior performance under high pressure in competitive situations. Although it is known that such situations affect the precompetitive activity of their autonomic nervous system (ANS), the relationship between precompetitive ANS activity and performance remains controversial. Especially in extreme sports, it has been shown that cardiac sympathetic tone occurs in athletes before competition attempts. However, the relationship between precompetitive sympathetic tone and performance is unclear. To investigate this relationship in extreme sports, we organized a freestyle snowboard jumping competition and examined competitors' physiological states and performance during this event. The electrocardiograms (ECGs) of 20 elite snowboarders were measured 10 min before each jump in different competitive situations: practice, qualifying, and final sessions. The mean heart rate (HR), the low-frequency to high-frequency component ratio (LF/HF ratio), the logarithm of the HF (lnHF) component of the frequency-domain of the heart rate variability (HRV), the ratio of the standard deviation of all R-R intervals to the root mean square of successive differences of R-R intervals (SDNN/rMSSD ratio), and the rMSSD of the time-domain of the HRV were calculated from the ECG data. The results showed a significant increase in the mean HR as well as significant decreases in the lnHF component and rMSSD of the HRV as the sessions progressed. Interestingly, the mean HR, LF/HF ratio and SDNN/rMSSD ratio of the HRV showed significant positive correlations with competitive scores, and the lnHF component and rMSSD of the HRV showed significant negative correlations with the scores. Our results indicate that precompetitive ANS activity becomes predominantly sympathetic in elite extreme athletes, such as freestyle snowboarders, when the competition intensifies, and that this sympathetic predominance is positively related to competitive performance.

Sexual dimorphism in rats exposed to maternal high fat diet: alterations in medullary sympathetic network

Exposure to high fat diet during perinatal period (PHFD) leads to neuroplastic changes in autonomic circuits, however, the role of gender has been incompletely understood. This study aims to investigate (i) short, and (ii) long-term effects of PHFD on autonomic outflow, and (iii) sexual dimorphic variations emerge at adulthood. Male and female rats were fed a control diet (13.5 % kcal from fat) or PHFD (60 % kcal from fat) from embryonic day-14 to postnatal day-21. To assess changes in autonomic outflow, heart rate variability (HRV) was analyzed at 10- and 20-week-old ages. Expressions of tyrosine hydroxylase (TH), metabotropic glutamate_2/3 receptor (mGlu_2/3R), N-methyl-D-aspartate₁ receptor (NMDA₁R), and gamma aminobutyric acid_A receptor (GABA_AR) were evaluated by immunohistochemistry. PHFD did not affect the body weight of 4-, 10-or 20-week-old male or female offsprings. PHFD significantly increased the sympathetic marker low frequency (LF) component, and sympatho-vagal balance (LF:HF) only in 10-week-old PHFD males. Compared with control, the propranolol-induced (4 mg·kg^- 1, ip) decline in LF was observed more prominently in PHFD rats, however, these changes were found to be restored at the age of 20 weeks. In caudal ventrolateral medulla and nucleus tractus solitarius, expression of mGlu_2/3R was downregulated in PHFD males, whereas no change was detected in NMDA₁R. The number of GABA_AR-expressing TH-immunoreactive cells was decreased in rostral ventrolateral medulla of PHFD males. The findings of this study suggest that exposure to maternal high-fat diet could lead to autonomic imbalance with increased sympathetic tone in the early adulthood of male offspring rats without developing obesity.

Advances in understanding the impacts of global warming on marine fishes farmed offshore: Sparus aurata as a case study

Monitoring variations in proteins involved in metabolic processes, oxidative stress responses, cell signalling and protein homeostasis is a powerful tool for developing hypotheses of how environmental variations affect marine organisms' physiology and biology. According to the oxygen- and capacity-limited thermal tolerance hypothesis, thermal acclimation mechanisms such as adjusting the activities of enzymes of intermediary metabolism and of antioxidant defence mechanisms, inducing heat shock proteins (Hsps) or activating mitogen-activated protein kinases may all shift tolerance windows. Few studies have, however, investigated the molecular, biochemical and organismal responses by fishes to seasonal temperature variations in the field to link these to laboratory findings. Investigation of the impacts of global warming on fishes farmed offsore, in the open sea, can provide a stepping stone towards understanding effects on wild populations because they experience similar environmental fluctuations. Over the last 30 years, farming of the gilthead sea bream Sparus aurata (Linnaeus 1758) has become widespread along the Mediterranean coastline, rendering this species a useful case study. Based on available information, the prevailing seasonal temperature variations expose the species to the upper and lower limits of its thermal range. Evidence for this includes oxygen restriction, reduced feeding, reduced responsiveness to environmental stimuli, plus a range of molecular and biochemical indicators that change across the thermal range. Additionally, close relationships between biochemical pathways and seasonal patterns of metabolism indicate a connection between energy demand and metabolic processes on the one hand, and cellular stress responses such as oxidative stress, inflammation and autophagy on the other. Understanding physiological responses to temperature fluctuations in fishes farmed offshore can provide crucial background information for the conservation and successful management of aquaculture resources in the face of global change.

Omeprazole induces vascular remodeling by mechanisms involving xanthine oxidoreductase and matrix metalloproteinase activation

Proton pump inhibitors (PPI) are commonly used drugs that may increase the cardiovascular risk by mechanisms not entirely known. We examined whether the PPI omeprazole promotes vascular oxidative stress mediated by xanthine oxidoreductase (XOR) leading to activation of matrix metalloproteinases (MMPs) and vascular remodeling. We studied Wistar rats treated with omeprazole (or vehicle) combined with the XOR inhibitor allopurinol (or vehicle) for four weeks. Systolic blood pressure (SBP) measured by tail-cuff plethysmography was not affected by treatments. Omeprazole treatment increased the aortic cross-sectional area and media/lumen ratio by 25% (P < 0.05). Omeprazole treatment decreased gastric pH and induced vascular remodeling accompanied by impaired endothelium-dependent aortic responses (assessed with isolated aortic ring preparation) to acetylcholine (P < 0.05). Omeprazole increased vascular active MMP-2 expression and activity assessed by gel zymography and in situ zymography, respectively (P < 0.05). Moreover, omeprazole enhanced vascular oxidative stress assessed in situ with the fluorescent dye DHE and with the lucigenin chemiluminescence assay (both P < 0.05). All these biochemical changes caused by omeprazole were associated with increased vascular XOR activity (but not XOR expression assessed by Western blot) and treatment with allopurinol fully prevented them (all P < 0.05). Importantly, treatment with allopurinol prevented the vascular dysfunction and remodeling caused by omeprazole. Our results suggest that the long-term use of omeprazole induces vascular dysfunction and remodeling by promoting XOR-derived reactive oxygen species formation and MMP activation. These findings provide evidence of a new mechanism that may underlie the unfavorable cardiovascular outcomes observed with PPI therapy. Clinical studies are warranted to validate our findings.

Comparison of nonparametric and parametric methods for time-frequency heart rate variability analysis in a rodent model of cardiovascular disease

The aim of time-varying heart rate variability spectral analysis is to detect and quantify changes in the heart rate variability spectrum components during nonstationary events. Of the methods available, the nonparametric short-time Fourier Transform and parametric time-varying autoregressive modeling are the most commonly employed. The current study (1) compares short-time Fourier Transform and autoregressive modeling methods influence on heart rate variability spectral characteristics over time and during an experimental ozone exposure in mature adult spontaneously hypertensive rats, (2) evaluates the agreement between short-time Fourier Transform and autoregressive modeling method results, and (3) describes the advantages and disadvantages of each method. Although similar trends were detected during ozone exposure, statistical comparisons identified significant differences between short-time Fourier Transform and autoregressive modeling analysis results. Significant differences were observed between methods for LF power (p ≤ 0.014); HF power (p ≤ 0.011); total power (p ≤ 0.027); and normalized HF power (p = 0.05). Furthermore, inconsistencies between exposure-related observations accentuated the lack of agreement between short-time Fourier Transform and autoregressive modeling overall. Thus, the short-time Fourier Transform and autoregressive modeling methods for time-varying heart rate variability analysis could not be considered interchangeable for evaluations with or without interventions that are known to affect cardio-autonomic activity.

Kynurenic acid selectively reduces heart rate in spontaneously hypertensive rats

We found previously that intravenous kynurenic acid (KYNA), a native broad spectrum glutamate antagonist, increases renal blood flow and induces natriuresis in anesthetized spontaneously hypertensive rats (SHR). Since such changes may affect systemic circulation and can potentially find therapeutic application, in this study we examined long term influence of orally administered KYNA on systemic and renal hemodynamics and renal excretion in conscious SHR. KYNA was administered in drinking water at a dose of 25 mg/kg/day for 3 weeks. Heart rate (HR), systolic (SBP), and mean arterial pressure (MAP) were measured through telemetry. The records were taken at the beginning of the study (control, day 0), and then on day 7, 14, and 21 of treatment. Diuresis (V), total solute excretion (U_osmV), and sodium excretion (U_NaV) were determined on days 0, 7, and 14. KYNA consistently decreased HR, from 319 ± 8 to 291 ± 5, 299 ± 9 and 284 ± 6 beats/min on day 7, 14, and 21, respectively, (- 9, - 6, and - 11%; p < 0.01-0.0001); HR was stable in the solvent group. SBP, MAP, V, and U_NaV were not affected by KYNA, whereas U_osmV increased modestly. Chronic oral administration of KYNA to conscious SHR decreased HR without affecting MAP. Since tachycardia is an independent risk factor for cardiovascular disorders, and most drugs used to decrease HR have strong inotropic negative or hypotensive effect, such selective action seems of therapeutic potential. Moreover, food supplementation with KYNA can be considered in the prevention of heart diseases.