Oxidative stress and antioxidant status in a lizard Phrynocephalus vlangalii at different altitudes or acclimated to hypoxia

Preparation for oxidative stress in Chinese toads (Bufo gargarizans) living under natural conditions along an altitudinal gradient

Preparation for oxidative stress (POS) has been widely reported in animals under controlled laboratory conditions, but whether this phenomenon is visible in animals under natural conditions remains to be explored. Altitudinal gradients provide a good opportunity to address this question, since environmental conditions become more hostile with increasing altitude. Here, we investigated the levels of oxidative stress, oxidative damage, and antioxidant defenses in Chinese toads (Bufo gargarizans) along an altitudinal gradient (50 m, 1200 m, 2300 m, 3400 m above sea level). The results show that changing altitude led to a significantly lower ratio of oxidized to reduced glutathione in liver, with a higher value at 50 m. This ratio in muscle tissues did not differ significantly between altitudes of 50 m, 2300 m, and 3400 m. However, reduced glutathione content increased significantly along the altitude, with higher values in liver at 2300 m and higher values in skeletal muscle at 3400 m. Malondialdehyde (MDA) content in liver did not change significantly with increasing altitude. Brain and muscle tissues showed a higher MDA content at 50 m than the other three altitudes. The activities of superoxide dismutase, catalase, glutathione peroxidase, and glutathione-S-transferase, as well as total antioxidant capacity, also displayed tissue-specific upregulation in heart, skeletal muscle, and brain, but all of these antioxidant enzymes except for glutathione-S-transferase were significantly reduced in liver along the altitudinal gradient. In summary, environmental factors at higher altitude did not lead to higher levels of oxidative stress and oxidative damage in B. gargarizans, mainly due to stronger antioxidant defenses. This study corroborates the occurrence of POS in high-altitude toads living under field conditions and contributes to revealing the biochemical adaptations to extreme environments at higher altitude.

REVIEW: Evidence supporting the 'preparation for oxidative stress' (POS) strategy in animals in their natural environment

Hypometabolism is a common strategy employed by resilient species to withstand environmental stressors that would be life-threatening for other organisms. Under conditions such as hypoxia/anoxia, temperature and salinity stress, or seasonal changes (e.g. hibernation, estivation), stress-tolerant species down-regulate pathways to decrease energy expenditures until the return of less challenging conditions. However, it is with the return of these more favorable conditions and the reactivation of basal metabolic rates that a strong increase of reactive oxygen and nitrogen species (RONS) occurs, leading to oxidative stress. Over the last few decades, cases of species capable of enhancing antioxidant defenses during hypometabolic states have been reported across taxa and in response to a variety of stressors. Interpreted as an adaptive mechanism to counteract RONS formation during tissue hypometabolism and reactivation, this strategy was coined "Preparation for Oxidative Stress" (POS). Laboratory experiments have confirmed that over 100 species, spanning 9 animal phyla, apply this strategy to endure harsh environments. However, the challenge remains to confirm its occurrence in the natural environment and its wide applicability as a key survival element, through controlled experimentation in field and in natural conditions. Under such conditions, numerous confounding factors may complicate data interpretation, but this remains the only approach to provide an integrative look at the evolutionary aspects of ecophysiological adaptations. In this review, we provide an overview of representative cases where the POS strategy has been demonstrated among diverse species in natural environmental conditions, discussing the strengths and weaknesses of these results and conclusions.

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.

Glutathione Depletion Disrupts Redox Homeostasis in an Anoxia-Tolerant Invertebrate

The upregulation of endogenous antioxidants is a widespread phenomenon in animals that tolerate hypoxia/anoxia for extended periods. The identity of the mobilized antioxidant is often context-dependent and differs among species, tissues, and stresses. Thus, the contribution of individual antioxidants to the adaptation to oxygen deprivation remains elusive. This study investigated the role of glutathione (GSH) in the control of redox homeostasis under the stress of anoxia and reoxygenation in Helix aspersa, an animal model of anoxia tolerance. To do so, the total GSH (tGSH) pool was depleted with l-buthionine-(S, R)-sulfoximine (BSO) before exposing snails to anoxia for 6 h. Then, the concentration of GSH, glutathione disulfide (GSSG), and oxidative stress markers (TBARS and protein carbonyl) and the activity of antioxidant enzymes (catalase, glutathione peroxidase, glutathione transferase, glutathione reductase, and glucose 6-phosphate dehydrogenase) were measured in foot muscle and hepatopancreas. BSO alone induced tGSH depletion by 59-75%, but no other changes happened in other variables, except for foot GSSG. Anoxia elicited a 110-114% increase in glutathione peroxidase in the foot; no other changes occurred during anoxia. However, GSH depletion before anoxia increased the GSSG/tGSH ratio by 84-90% in both tissues, which returned to baseline levels during reoxygenation. Our findings indicate that glutathione is required to withstand the oxidative challenge induced by hypoxia and reoxygenation in land snails.

Does oxidative stress shorten telomeres in vivo? A meta-analysis

Telomere attrition is considered a hallmark of ageing. Untangling the proximate causes of telomere attrition may therefore reveal important aspects about the ageing process. In a landmark paper in 2002 Thomas von Zglinicki demonstrated that oxidative stress accelerates telomere attrition in cell culture. In the next 20 years, oxidative stress became firmly embedded into modern theories of ageing and telomere attrition. However, a recent surge of in vivo studies reveals an inconsistent pattern questioning the unequivocal role of oxidative stress in telomere length and telomere attrition (henceforth referred to as telomere dynamics), in living organisms. Here we report the results of the first formal meta-analysis on the association between oxidative stress and telomere dynamics in vivo, representing 37 studies, 4969 individuals, and 18,677 correlational measurements. The overall correlation between oxidative stress markers and telomere dynamics was indistinguishable from zero (r = 0.027). This result was independent of the type of oxidative stress marker, telomere dynamic, or taxonomic group. However, telomere measurement method affected the analysis and the subset of TRF-based studies showed a significant overall correlation (r = 0.09), supporting the prediction that oxidative stress accelerates telomere attrition. The correlation was more pronounced in short-lived species and during the adult life phase, when ageing becomes apparent. We then performed an additional meta-analysis of interventional studies (n = 7) manipulating oxidative stress. This revealed a significant effect of treatment on telomere dynamics (d=0.36). Our findings provide new support for the hypothesis that oxidative stress causes telomere attrition in living organisms.

Disrupted gut microbiota aggravates working memory dysfunction induced by high-altitude exposure in mice

BACKGROUND

The widely accepted microbiome-gut-brain axis (MGBA) hypothesis may be essential for explaining the impact of high-altitude exposure on the human body, especially brain function. However, studies on this topic are limited, and the underlying mechanism remains unclear. Therefore, this study aimed to determine whether high-altitude-induced working memory dysfunction could be exacerbated with gut microbiota disruption.

METHODS AND RESULTS

C57BL/6 mice were randomly divided into three groups: control, high-altitude exposed (HAE), and high-altitude exposed with antibiotic treatment (HAE-A). The HAE and HAE-A groups were exposed to a low-pressure oxygen chamber (60-65 kPa) simulating the altitude of 3,500-4,000 m for 14 days, The air pressure level for the control group was maintained at 94.5 kPa. Antibiotic water (mixed with 0.2 g/L of ciprofloxacin and 1 g/L of metronidazole) was provided to the HAE-A group. Based on the results of the novel object test and P300 in the oddball behavioral paradigm training test, working memory dysfunction was aggravated by antibiotic treatment. We determined the antioxidant capacity in the prefrontal cortex and found a significant negative influence (p < 0.05) of disturbed gut microbiota on the total antioxidant capacity (T-AOC) and malondialdehyde (MDA) content, as well as the activities of superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px). The same trend was also observed in the apoptosis-related functional protein content and mRNA expression levels in the prefrontal cortex, especially the levels of bcl-2, Bax, and caspase-3. The high-altitude environment and antibiotic treatment substantially affected the richness and diversity of the colonic microbiota and reorganized the composition and structure of the microbial community. S24-7, Lachnospiraceae, and Lactobacillaceae were the three microbial taxa with the most pronounced differences under the stimulation by external factors in this study. In addition, correlation analysis between colonic microbiota and cognitive function in mice demonstrated that Helicobacteraceae may be closely related to behavioral results.

CONCLUSION

Disrupted gut microbiota could aggravate working memory dysfunction induced by high-altitude exposure in mice, indicating the existence of a link between high-altitude exposure and MGBA.

Physiological and Biochemical Adaptations to High Altitude in Tibetan Frogs, Nanorana parkeri

The Xizang plateau frog, N. parkeri (Anura: Dicroglossidae), is endemic to the Tibetan Plateau, ranging from 2,850 to 5,100 m above sea level. The present study explores physiological and biochemical adaptations to high altitude in this species with a particular emphasis on parameters of hematology, oxidative stress, and antioxidant defense in adult and juvenile N. parkeri collected from high (4,600 m a.s.l) and low (3,400 m a.s.l) altitudes. Hematological results showed that hemoglobin concentration ([Hb]), hematocrit (Hct), and red blood cell (RBC) counts were significantly higher in high-altitude N. parkeri. High-altitude juveniles had lower RBC sizes than low-altitude juveniles. Higher levels of GSH and GSSG were indicated only in juveniles from high altitude, not in adults. High-altitude individuals also showed lower oxidative damage, assessed as malondialdehyde (MDA) and carbonyl groups (CG) in the liver. High-altitude adults also showed higher activities of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPX), and glutathione-S-transferase (GST) as well as total antioxidant capacity (T-AOC) in the liver as compared to low-altitude adults. Moreover, higher GPX activity and T-AOC were observed in the heart and brain of high-altitude adults. Liver CAT, GPX, and T-AOC showed significant increases in high-altitude juveniles. Vitamin C content was also higher in the heart of high-altitude frogs compared to low-altitude individuals. In summary, the high-altitude population of N. parkeri showed more robust hematological parameters, less oxidative damage, and stronger antioxidant defenses than the low-altitude population, all contributing to increased protection for survival in high-altitude environments.

Oxidative and osmotolerant effects in Salvator merianae (Squamata: Teiidae) red blood cells during hibernation

Hibernation is a natural condition of animals that lives in the temperate zone, although some tropical lizards also experience hibernation annually, such as the lizard native from South America, Salvator merianae, or "tegu" lizard. Even though physiological and metabolic characteristic associated with hibernation have been extensively studied, possible alterations in the red blood cells (RBC) integrity during this period remains unclear. Dehydration and fasting are natural consequences of hibernating for several months and it could be related to some cellular modifications. In this study, we investigated if the osmotic tolerance of RBCs of tegu lizard under hibernation is different from the cells obtained from animals while normal activity. Additionally, we indirectly investigated if the RBCs membrane of hibernating tegus could be associated with oxidation by quantifying oxidized biomolecules and the activity of antioxidant enzymes. Our findings suggest that RBCs are more fragile during the hibernation period, although we did not find evidence of an oxidative stress scenario associated with the accentuated fragility. Even though we did not exclude the possibility of oxidative damage during hibernation, we suggested that an increased RBCs volume as a consequence of hypoosmotic blood during hibernation could also affect RBCs integrity as noted.

HgS Inhibits Oxidative Stress Caused by Hypoxia through Regulation of 5-HT Metabolism Pathway

This study aims to reveal the potential relationship between 5-HT and oxidative stress in the organism. Our in vitro experiments in RIN-14B cells showed that anoxia leads the cells to the state of oxidative stress. Administration of exogenous 5-HT exacerbated this effect, whereas the inhibition of Tph1, LP533401 alleviated the oxidative stress. Several research articles reported that Cinnabar (consists of more than 96% mercury sulfide, HgS), which is widely used in both Chinese and Indian traditional medicine prescriptions, has been involved in the regulation of 5-HT. The present research revealed that HgS relieved the level of oxidative stress of RIN-14B cells. This pharmacological activity was also observed in the prescription drug Zuotai, in which HgS accounts for 54.5%, and these effects were found to be similar to LP533401, an experimental drug to treat pulmonary hypertension. Further, our in vivo experiments revealed that the administration of cinnabar or prescription drug Zuotai in zebrafish reduced the reactive oxygen species (ROS) induced by hypoxia and cured behavioral abnormalities. Taken together, in organisms with hypoxia induced oxidative stress 5-HT levels were found to be abnormally elevated, indicating that 5-HT could regulate oxidative stress, and the decrease in the 5-HT levels, behavioral abnormalities after treatment with cinnabar and Zuotai, we may conclude that the therapeutic and pharmacologic effect of cinnabar and Zuotai may be based on the regulation of 5-HT metabolism and relief of oxidative stress. Even though they aren't toxic at the present dosage in both cell lines and zebrafish, their dose dependent toxicities are yet to be evaluated.

Changes of 8-OHdG and TrxR in the Residents Who Bathe in Radon Hot Springs

This study explored the effects of long-term bathing in radon hot springs on oxidative damage and antioxidation function in humans. In this study, blood was collected from residents in the Pingshan radon hot spring area (RHSA), Jiangzha RHSA, and control area (CA). 8-Hydroxydeoxyguanosine (8-OHdG) and thioredoxin reductase (TrxR), representing oxidation and antioxidant levels, respectively, were analyzed as indices. Compared to the CA group, the RHSA group in the Pingshan and Jiangzha areas showed significantly decreased 8-OHdG levels (Z = -3.350, -3.316, respectively, P < .05) and increased TrxR levels (Z = 2.394, 3.773, respectively, P < .05). The RHSA and CA groups in Jiangzha had lower levels of TrxR and 8-OHdG compared to those in Pingshan. This finding may be related to the different radon concentration levels, bathing time and other factors. Results suggested that long-term bathing in radon hot spring may activate antioxidant function and reduce oxidative damage in the body.

Do Bar-Headed Geese Train for High Altitude Flights?

SYNOPSIS

Exercise at high altitude is extremely challenging, largely due to hypobaric hypoxia (low oxygen levels brought about by low air pressure). In humans, the maximal rate of oxygen consumption decreases with increasing altitude, supporting progressively poorer performance. Bar-headed geese (Anser indicus) are renowned high altitude migrants and, although they appear to minimize altitude during migration where possible, they must fly over the Tibetan Plateau (mean altitude 4800 m) for much of their annual migration. This requires considerable cardiovascular effort, but no study has assessed the extent to which bar-headed geese may train prior to migration for long distances, or for high altitudes. Using implanted loggers that recorded heart rate, acceleration, pressure, and temperature, we found no evidence of training for migration in bar-headed geese. Geese showed no significant change in summed activity per day or maximal activity per day. There was also no significant change in maximum heart rate per day or minimum resting heart rate, which may be evidence of an increase in cardiac stroke volume if all other variables were to remain the same. We discuss the strategies used by bar-headed geese in the context of training undertaken by human mountaineers when preparing for high altitude, noting the differences between their respective cardiovascular physiology.

High-Altitude Living Shapes the Skin Microbiome in Humans and Pigs

While the skin microbiome has been shown to play important roles in health and disease in several species, the effects of altitude on the skin microbiome and how high-altitude skin microbiomes may be associated with health and disease states remains largely unknown. Using 16S rRNA marker gene sequencing, we characterized the skin microbiomes of people from two racial groups (the Tibetans and the Hans) and of three local pig breeds (Tibetan pig, Rongchang pig, and Qingyu pig) at high and low altitudes. The skin microbial communities of low-altitude pigs and humans were distinct from those of high-altitude pigs and humans, with five bacterial taxa (Arthrobacter, Paenibacillus, Carnobacterium, and two unclassified genera in families Cellulomonadaceae and Xanthomonadaceae) consistently enriched in both pigs and humans at high altitude. Alpha diversity was also significantly lower in skin samples collected from individuals living at high altitude compared to individuals at low altitude. Several of the taxa unique to high-altitude humans and pigs are known extremophiles adapted to harsh environments such as those found at high altitude. Altogether our data reveal that altitude has a significant effect on the skin microbiome of pigs and humans.

Organ Mass Variation in a Toad Headed Lizard Phrynocephalus vlangalii in Response to Hypoxia and Low Temperature in the Qinghai-Tibet Plateau, China

Hypoxia and low temperature at high altitudes are the main environmental pressures for alpine animals, inducing phenotypic plasticity at several levels. To investigate the effect of these variables on the organ mass of Phrynocephalus vlangalii, 138 individuals belonging to four populations living along an altitudinal gradient in the Qinghai-Tibet Plateau (China) were dissected to remove heart, lungs, stomach, and intestinal tract. Organ dry mass, individuals’ sex, and body mass, as well as mean annual temperature and average air pressure (calculated from a 30-year-data series obtained from the National Climatic Data Center) were subjected to two-way analyses of covariance and generalized linear mixed models (GLMMs). Except for the heart, organ mass varied significantly among populations, although only lung and stomach mass increased significantly with increasing altitude. Males’ heart and lung mass was higher than that of females, which might be due to their different behavior and reproductive efforts. GLMM analyses indicated that air pressure had a positive effect on heart, lung and intestinal tract mass, whereas temperature had a negative effect on these three organs. In order to explain the effect of hypoxia and low temperature on P. vlangalii’s organ mass, further rigorous study on respiration, energy budget and food intake was encouraged.