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

Abstract

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.

The role of glucocorticoids in naturally fasting grey seal (Halichoerus grypus) pups: dexamethasone stimulates mass loss and protein utilisation, but not departure from the colony

“…Most phocid pups fast on land after weaning, during which time they undergo physiological changes that prepare them for diving (Burns et al, 2007;Lewis et al, 2001;Noren et al, 2005;Soñanez-Organis et al, 2012;Thorson and Le Boeuf, 1994;Vásquez-Medina et al, 2010;Vásquez-Medina et al, 2011). The duration of the postweaning fast has a positive effect on diving capabilities when pups first go to sea (Bennett et al, 2010).…”

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

“…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.…”

Prolonged fasting activates Nrf2 in postweaned elephant seals

“…An increase in GSH levels and antioxidant enzyme expression at the end of the fast (Vázquez-Medina et al, 2010;Vázquez-Medina et al, 2011b) may potentially ameliorate the oxidant generation derived from augmented XO and Nox expression and activity (Soñanez-Organis et al, 2012;Vázquez-Medina et al, 2010), impaired insulin signaling (Fowler et al, 2008;Viscarra et al, 2011a;Viscarra et al, 2011b), high rates of glucose auto-oxidation (Champagne et al, 2005;Champagne et al, 2012;Houser et al, 2012) and lipid oxidation (Viscarra et al, 2012), RAS activation (Ortiz et al, 2006;Ortiz et al, 2001) and chronic HPA stimulation (Ortiz et al, 2003a;Ortiz et al, 2001). Increased antioxidant defenses at the end of the fast are also consistent with an increase in the number and duration of sleep apnea bouts that normally last between 8 and 12min and constitute 80% of the seals' time on land (Blackwell and Boeuf, 1993;Castellini et al, 1994), along with increases in the time spent submerged in near-shore waters (Thorson and Le Boeuf, 1994).…”

“…In the northern elephant seal, prolonged fasting increases Nox4 and xanthine oxidase (XO) without increasing oxidative damage or inflammation (Soñanez-Organis et al, 2012;Vázquez-Medina et al, 2010). Systemic and muscle markers of oxidative damage (F 2 -isoprostanes, nitrotyrosine, C-reactive protein, tumor necrosis factor α (TNF-α), 4-hydroxynonenal, protein carbonyls) remain unchanged after 2months of absolute fasting in seal pups (Vázquez-Medina et al, 2010).…”

“…Systemic and muscle markers of oxidative damage (F 2 -isoprostanes, nitrotyrosine, C-reactive protein, tumor necrosis factor α (TNF-α), 4-hydroxynonenal, protein carbonyls) remain unchanged after 2months of absolute fasting in seal pups (Vázquez-Medina et al, 2010). Fasting-related increases in the activity and protein expression of several antioxidant enzymes and glutathione (GSH) levels (Vázquez-Medina et al, 2010;Vázquez-Medina et al, 2011b), as well as increased purine recycling (Soñanez-Organis et al, 2012), likely contribute to the prevention of oxidative damage in elephant seals.…”