Prolonged fasting does not increase oxidative damage or inflammation in postweaned northern elephant seal pups

Abstract

SUMMARYElephant seals are naturally adapted to survive up to three months of absolute food and water deprivation (fasting). Prolonged food deprivation in terrestrial mammals increases reactive oxygen species (ROS) production, oxidative damage and inflammation that can be induced by an increase in the renin-angiotensin system (RAS). To test the hypothesis that prolonged fasting in elephant seals is not associated with increased oxidative stress or inflammation, blood samples and muscle biopsies were collected from early (2-3 weeks post-weaning) and late (7-8 weeks post-weaning) fasted seals. Plasma levels of oxidative damage, inflammatory markers and plasma renin activity (PRA), along with muscle levels of lipid and protein oxidation, were compared between early and late fasting periods. Protein expression of angiotensin receptor 1 (AT 1 ), pro-oxidant (Nox4) and antioxidant enzymes (CuZn-and Mn-superoxide dismutases, glutathione peroxidase and catalase) was analyzed in muscle. Fasting induced a 2.5-fold increase in PRA, a 50% increase in AT 1 , a twofold increase in Nox4 and a 70% increase in NADPH oxidase activity. By contrast, neither tissue nor systemic indices of oxidative damage or inflammation increased with fasting. Furthermore, muscle antioxidant enzymes increased 40-60% with fasting in parallel with an increase in muscle and red blood cell antioxidant enzyme activities. These data suggest that, despite the observed increases in RAS and Nox4, an increase in antioxidant enzymes appears to be sufficient to suppress systemic and tissue indices of oxidative damage and inflammation in seals that have fasted for a prolonged period. The present study highlights the importance of antioxidant capacity in mammals during chronic periods of stress to help avoid deleterious systemic consequences.

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

“…Blood samples were collected into EDTA-treated collection tubes containing 10lml -1 protease inhibitor cocktail and 0.005% butylated hydroxytoluene (Sigma, St Louis, MO, USA) and centrifuged on site for 15min at 3000g before plasma was aliquoted into separate cryovials. Adipose tissue and muscle biopsies (20-40mg) were collected from a small region in the flank of the animal near the hind flipper, as described previously (Vázquez-Medina et al, 2010;Vázquez-Medina et al, 2011a). Plasma and tissue samples were frozen by immersion in liquid nitrogen immediately after collection and stored at -80°C until analyzed.…”

“…Plasma HGPRT and XO activities increased (P<0.05) at each week across the fasting over the 7week measurement period (Fig.4C,D). cortisol, non-esterified fatty acids and promoting insulin resistance (Ortiz et al, 2000;Ortiz et al, 2001;Ortiz et al, 2003;Ortiz et al, 2006;Vázquez-Medina et al, 2010;Viscarra et al, 2011a;Viscarra et al, 2011b). Unfortunately, the molecular and physiological mechanisms adopted by seals to cope with prolonged fasting are not fully elucidated.…”

“…In humans, rats and mice, prolonged fasting increases oxidant production, oxidative damage and inflammation (Crescimanno et al, 1989;Di Simplicio et al, 1997;Grattagliano et al, 2000;Kondoh et al, 2003;Mårtensson, 1986;Sorensen et al, 2006;Souza Rocha et al, 2008;Wu et al, 2004). In elephant seals, prolonged fasting does not induce oxidative damage or inflammation despite promoting the chronic activation of the renin-angiotensin system (RAS) and increasing circulating cortisol, NADPH oxidase activity, Nox4 protein expression and insulin resistance (Ortiz et al, 2000;Ortiz et al, 2002;Vázquez-Medina et al, 2010;Viscarra et al, 2011a;Viscarra et al, 2011b).…”

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

“…Samples were extracted using ethanol, 30% acetic acid and C-18 solid phase extraction cartridges. Plasma and muscle levels of nitrotyrosine (NT) and 4-hydroxynonenal (HNE), as well as plasma carbonyls, were also measured using commercially available ELISA kits (Cell BioLabs, San Diego, CA, USA) (Vázquez-Medina et al, 2010). Plasma XO activity and xanthine and HX concentrations were measured using an Amplex ® Red assay kit (Molecular Probes, Eugene, OR, USA).…”

“…Although bouts of sleep apnea occur in all elephant seals regardless of age, weaned pups increase the number and duration of apneas at the end of their postweaning fast, when seals are learning to swim and dive, and just prior to initiating their diving lifestyle (Blackwell and Le Boeuf, 1993). Elephant seal pups also increase their antioxidant defenses at the end of their postweaning fast, suggesting that the activation of the antioxidant system in these mammals is an essential part of their developmental process and prepares them to dive, which is the next step in their life history (Vázquez-Medina et al, 2010;Vázquez-Medina et al, 2011c) suggest that, because apnea stimulates the adaptive response to oxidative stress, and the number and duration of apneas increase with development in elephant seal pups, apnea is essential to prime the seal's antioxidant mechanisms that allow them to cope with the subsequent diving-induced hypoxemia and ischemia/reperfusion/ reoxygenation while at sea. Maturation-related increases in antioxidant capacity have also been documented in the deep-diving hooded seal (Vázquez-Medina et al, 2011a;Vázquez-Medina et al, 2011b), in which oxygen stores (hemoglobin and Mb content), acid buffering capacity, and aerobic and anaerobic enzyme activities also increase with maturation in the skeletal muscle (Burns et al, 2007;Burns et al, 2010;Lestyk et al, 2009).…”