Apnea stimulates the adaptive response to oxidative stress in elephant seal pups

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Low concentrations of endogenous carbon monoxide (CO), generated primarily through degradation of heme from hemeproteins, have been shown to maintain physiological function of organs and to exert cytoprotective effects. However, high concentrations of carboxyhemoglobin (COHb), formed by CO binding to hemoglobin, potentially prevent adequate O 2 delivery to tissues by lowering arterial O 2 content. Elevated heme-protein concentrations, as found in marine mammals, are likely associated with greater heme degradation, more endogenous CO production and, consequently, elevated COHb concentrations. Therefore, we measured COHb in elephant seals, a species with large blood volumes and elevated hemoglobin and myoglobin concentrations. The levels of COHb were positively related to the total hemoglobin concentration. The maximum COHb value was 10.4% of total hemoglobin concentration. The mean (±s.e.m.) value in adult seals was 8.7±0.3% (N=6), while juveniles and pups (with lower heme-protein contents) had lower mean COHb values of 7.6±0.2% and 7.1±0.3%, respectively (N=9 and N=9, respectively). Serial samples over several hours revealed little to no fluctuation in COHb values. This consistent elevation in COHb suggests that the magnitude and/or rate of heme-protein turnover is much higher than in terrestrial mammals. The maximum COHb values from this study decrease total body O 2 stores by 7%, thereby reducing the calculated aerobic dive limit for this species. However, the constant presence of elevated CO in blood may also protect against potential ischemia-reperfusion injury associated with the extreme breath-holds of elephant seals. We suggest the elephant seal represents an ideal model for understanding the potential cytoprotective effects, mechanisms of action and evolutionary adaptation associated with chronically elevated concentrations of endogenously produced CO. KEY WORDS: Calculated aerobic dive limit, Carbon monoxide, Hemoglobin absorption spectra, Marine mammal, Oxygen stores INTRODUCTIONCarbon monoxide (CO) is often classified as a strictly toxic gas, depriving the body of oxygen (O 2 ) by binding to heme-proteins such as hemoglobin and forming carboxyhemoglobin (COHb) (Weaver, 2009). Deleterious symptoms (e.g. headache, nausea and shortness of breath) of CO-driven hypoxia are typically seen when COHb values reach ≥20% of total hemoglobin concentration, and death is associated with values of 50-80% (Stewart, 1975;Weaver, 2009 storage capacity (decreased arterial O 2 content), thus limiting mitochondrial respiration. However, CO is also generated endogenously in low concentrations, and functions in neurotransmission and in protection of tissues and cells against inflammation, apoptosis and ischemia-reperfusion injuries (Snyder et al., 1998; Kevin and Laffey, 2008;Mustafa et al., 2009; Kajimura et al., 2010;Prabhakar, 2012). Therefore, low concentrations of CO can provide beneficial and therapeutic effects up to a specific concentration, at which elevated CO then leads to detrimental effects from reduce...

Section: Potential Therapeutic Benefits Of Elevated Co In Marine Mammalsmentioning

confidence: 95%

Elevated carboxyhemoglobin in a marine mammal, the northern elephant seal

Tift

Ponganis

Crocker

2014

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“…The increase in the number and duration of sleep apneas is associated with an increase in antioxidants (Vázquez-Medina et al, 2010;Vázquez-Medina et al, 2011b) over the course of the post-weaning fast. Furthermore, it was recently demonstrated that plasma XO activity, HX and xanthine content increase in elephant seal pups in response to rest-and voluntary submersion-associated apneas (Vázquez-Medina et al, 2011c). Therefore, fasting and sleep apnea may stimulate ATP degradation, increasing intracellular and circulating oxidant production, potentially modulated by increased purine salvage/recycling pathways (Elsner et al, 1998;ZentenoSavín et al, 2002).…”

Section: Purine Metabolism Increases With Fastingmentioning

confidence: 99%

Prolonged fasting increases purine recycling in post-weaned northern elephant seals

Soñanez‐Organis

Vázquez‐Medina

Zenteno‐Savín³

et al. 2012

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SUMMARYNorthern elephant seals are naturally adapted to prolonged periods (1-2months) of absolute food and water deprivation (fasting). In terrestrial mammals, food deprivation stimulates ATP degradation and decreases ATP synthesis, resulting in the accumulation of purines (ATP degradation byproducts). Hypoxanthine-guanine phosphoribosyl transferase (HGPRT) salvages ATP by recycling the purine degradation products derived from xanthine oxidase (XO) metabolism, which also promotes oxidant production. The contributions of HGPRT to purine recycling during prolonged food deprivation in marine mammals are not well defined. In the present study we cloned and characterized the complete and partial cDNA sequences that encode for HGPRT and xanthine oxidoreductase (XOR) in northern elephant seals. We also measured XO protein expression and circulating activity, along with xanthine and hypoxanthine plasma content in fasting northern elephant seal pups. Blood, adipose and muscle tissue samples were collected from animals after 1, 3, 5 and 7weeks of their natural post-weaning fast. The complete HGPRT and partial XOR cDNA sequences are 771 and 345bp long and encode proteins of 218 and 115 amino acids, respectively, with conserved domains important for their function and regulation. XOR mRNA and XO protein expression increased 3-fold and 1.7-fold with fasting, respectively, whereas HGPRT mRNA (4-fold) and protein (2-fold) expression increased after 7weeks in adipose tissue and muscle. Plasma xanthine (3-fold) and hypoxanthine (2.5-fold) levels, and XO (1.7-to 20-fold) and HGPRT (1.5-to 1.7-fold) activities increased during the last 2weeks of fasting. Results suggest that prolonged fasting in elephant seal pups is associated with increased capacity to recycle purines, which may contribute to ameliorating oxidant production and enhancing the supply of ATP, both of which would be beneficial during prolonged food deprivation and appear to be adaptive in this species.

“…Biopsies were rinsed with cold, sterile saline, placed in cryogenic vials, immediately frozen by immersion in liquid nitrogen, and stored at −80°C until later analyses. Frozen tissue samples were homogenized in 500 μl of hypotonic buffer containing a protease and phosphatase inhibitor cocktail (Sigma-Aldrich, St Louis, MO, USA) as previously described (Vázquez-Medina et al, 2011;Viscarra et al, 2011a;Viscarra et al, 2011b;Vázquez-Medina et al, 2012;Viscarra et al, 2012). Nuclear and cytosolic extractions were performed using the Nuclear and Cytoplasmic Extraction Reagents Kit (Thermo Fisher Scientific, Waltham, MA, USA).…”

Section: Sample Collection and Preparationmentioning

confidence: 99%

“…Because our hypothesis focused on the changes in the deiodinases and the TH receptor, these proteins were given priority. Protein expression was quantified by standard western blot as previously described (Vázquez-Medina et al, 2011;Viscarra et al, 2011a;Viscarra et al, 2011b;Vázquez-Medina et al, 2012;Soñanez-Organis et al, 2012;Viscarra et al, 2012). The primary antibodies for DI1 and DI2, THrβ1, TATA binding protein, histone H3 and β-actin (Santa Cruz Biotechnology, Santa Cruz, CA) were diluted 1:500 to 1:5000.…”

Section: Quantification Of Protein Expression By Western Blottingmentioning

confidence: 99%

Prolonged food deprivation increases mRNA expression of deiodinase 1 and 2, and thyroid hormone receptor β-1 in a fasting-adapted mammal

Martinez

Soñanez‐Organis

Vázquez‐Medina

et al. 2013

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SUMMARYFood deprivation in mammals is typically associated with reduced thyroid hormone (TH) concentrations and deiodinase content and activity to suppress metabolism. However, in prolonged-fasted, metabolically active elephant seal pups, TH levels are maintained, if not elevated. The functional relevance of this apparent paradox is unknown and demonstrates variability in the regulation of TH levels, metabolism and function in food-deprived mammals. To address our hypothesis that cellular TH-mediated activity is upregulated with fasting duration, we quantified the mRNA expression and protein content of adipose and muscle deiodinase type I (DI1) and type II (DI2), and TH receptor beta-1 (THrβ-1) after 1, 3 and 7 weeks of fasting in northern elephant seal pups (N=5-7 per week). Fasting did not decrease the concentrations of plasma thyroid stimulating hormone, total triiodothyronine (tT 3 ), free T 3 , total thyroxine (tT 4 ) or free T 4 , suggesting that the hypothalamic-pituitary-thyroid axis is not suppressed, but rather maintained during fasting. Mean mRNA expression of adipose DI1 and DI2 increased threefold and fourfold, respectively, and 20-and 30-fold, respectively, in muscle. With the exception of adipose DI1, protein expression of adipose DI2 and muscle DI1 and DI2 increased twofold to fourfold. Fasting also increased adipose (fivefold) and muscle (fourfold) THrβ-1 mRNA expression, suggesting that the mechanisms mediating cellular TH activity are upregulated with prolonged fasting. The data demonstrate a unique, atypical mechanism of TH activity and regulation in mammals adapted to prolonged food deprivation in which the potential responsiveness of peripheral tissues and cellular TH activity are increased, which may contribute to their lipid-based metabolism.Key words: lipid metabolism, reverse T3, seal, thyroxine, triiodothyronine. THE JOURNAL OF EXPERIMENTAL BIOLOGY 4648 concentration in hibernating ground squirrels results from reduced TH metabolism, accompanied by a reduction in nuclear receptors, suggesting that TH function is suppressed despite the increase in circulating levels (i.e. cryptically hyperthyroid) (Magnus and Henderson, 1988a;Magnus and Henderson, 1988b). Such variability in the regulation of TH levels and function in food-deprived mammals demonstrates the diversity of TH physiology during periods of acute or chronic food deprivation, and highlights the necessity to perform more comprehensive studies into the functional relevance of these differences.Northern elephant seals, Mirounga angustirostris (Gill 1866), naturally fast from food and water for up to 3 months while on land (Ortiz et al., 1978; Crocker et al., 1998;Le Boeuf and Laws, 1994), and during the post-weaning fast, oxidation of non-esterified fatty acids (NEFAs) accounts for approximately 95% of the pup's metabolic rate (Ortiz et al., 1978;Viscarra et al., 2012). The fasting metabolism of seals is primarily dependent on lipid oxidation (Crocker et al., 1998;Pramfalk et al., 2011; Crocker et al., 2012a; Crocker et al., 2012...