Carbon monoxide (CO) has long been considered a toxic gas but is now a recognized bioactive gasotransmitter with potent immunomodulatory effects. Although inhaled CO is currently under investigation for use in patients with lung disease, this mode of administration can present clinical challenges. The capacity to deliver CO directly and safely to the gastrointestinal (GI) tract could transform the management of diseases affecting the GI mucosa such as inflammatory bowel disease or radiation injury. To address this unmet need, inspired by molecular gastronomy techniques, we have developed a family of gas-entrapping materials (GEMs) for delivery of CO to the GI tract. We show highly tunable and potent delivery of CO, achieving clinically relevant CO concentrations in vivo in rodent and swine models. To support the potential range of applications of foam GEMs, we evaluated the system in three distinct disease models. We show that a GEM containing CO dose-dependently reduced acetaminophen-induced hepatocellular injury, dampened colitis-associated inflammation and oxidative tissue injury, and mitigated radiation-induced gut epithelial damage in rodents. Collectively, foam GEMs have potential paradigm-shifting implications for the safe therapeutic use of CO across a range of indications.

SUMMARY Extended breath-hold (apnea) bouts are routine during diving and sleeping in seals. These apneas result in oxygen store depletion and blood flow redistribution towards obligatory oxygen-dependent tissues, exposing seals to critical levels of ischemia and hypoxemia. The subsequent reperfusion/reoxygenation has the potential to increase oxidant production and thus oxidative stress. The contributions of extended apnea to oxidative stress in adapted mammals are not well defined. To address the hypothesis that apnea in seals is not associated with increased oxidative damage, blood samples were collected from northern elephant seal pups (N=6) during eupnea, rest- and voluntary submersion-associated apneas, and post-apnea (recovery). Plasma 4-hydroxynonenal (HNE), 8-isoprostanes (8-isoPGF_2α), nitrotyrosine (NT), protein carbonyls, xanthine and hypoxanthine (HX) levels, along with xanthine oxidase (XO) activity, were measured. Protein content of XO, superoxide dismutase 1 (Cu,ZnSOD), catalase and myoglobin (Mb), as well as the nuclear content of hypoxia inducible factor 1α (HIF-1α) and NF-E2-related factor 2 (Nrf2), were measured in muscle biopsies collected before and after the breath-hold trials. HNE, 8-iso PGF_2α, NT and protein carbonyl levels did not change among eupnea, apnea or recovery. XO activity and HX and xanthine concentrations were increased at the end of the apneas and during recovery. Muscle protein content of XO, CuZnSOD, catalase, Mb, HIF-1α and Nrf2 increased 25–70% after apnea. Results suggest that rather than inducing the damaging effects of hypoxemia and ischemia/reperfusion that have been reported in non-diving mammals, apnea in seals stimulates the oxidative stress and hypoxic hormetic responses, allowing these mammals to cope with the potentially detrimental effects associated with this condition.

The cost of pregnancy is hard to study in marine mammals, particularly in species that undergo pregnancy while diving continuously at sea such as elephant seals (genus Mirounga ). We analysed the diving behaviour of confirmed pregnant and non-pregnant northern elephant seals ( M. angustirostris , n = 172) and showed that after an initial continuous increase in dive duration, dives of pregnant females become shorter after week 17. The reasons for this reduction in dive duration remain unknown, but we hypothesize that increased fetal demand for oxygen could be the cause. Our findings reveal an opportunity to explore the use of biologging data to investigate pregnancy status of free-ranging marine mammals and factors that could affect pregnancy success.

SUMMARY: Many polygynous, capital breeders exhibit sexual dimorphism with respect to body size and composition. Sexual dimorphism is often facilitated by sex differences in foraging behavior, growth rates and patterns of nutrient deposition during development. In species that undergo extended fasts during development, metabolic strategies for fuel use have the potential to influence future reproductive success by directly impacting somatic growth and acquisition of traits required for successful breeding. We investigated sexual dimorphism associated with metabolic strategies for fasting in developing northern elephant seals. Thirty-one juvenile seals of both sexes were sampled over extended fasts during annual autumn haul-outs. Field metabolic rate (FMR) and the contribution of protein catabolism to energy expenditure were estimated from changes in mass and body composition over 23±5 days of fasting (mean ± s.d.). Protein catabolism was assessed directly in a subset of animals based on urea flux at the beginning and end of the fast. Regulatory hormones and blood metabolites measured included growth hormone, cortisol, thyroxine, triiodothyronine, insulin, glucagon, testosterone, estradiol, glucose, urea and β-hydroxybutyrate. Males exhibited higher rates of energy expenditure during the fast but spared body protein stores more effectively than females. Rates of protein catabolism and energy expenditure were significantly impacted by hormone levels, which varied between the sexes. These data suggest that sex differences in fuel metabolism and energy expenditure during fasting arise early in juvenile development and may play an important role in the development of adult traits associated with reproductive success.

Low concentrations of endogenous carbon monoxide (CO), generated primarily through degradation of heme from heme-proteins, 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 O₂ delivery to tissues by lowering arterial O₂ 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 O₂ 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.

Heme oxygenase (HO) enzymes catalyze heme into biliverdin, releasing carbon monoxide (CO) and iron into circulation. These byproducts of heme degradation can have potent cytoprotective effects in the face of stressors such as hypoxia and ischemia-reperfusion events. The potential for exogenous use of CO as a therapeutic agent has received increasing attention throughout the past few decades. Further, HO and CO are noted as putatively adaptive in diving mammals and certain high-altitude human populations that are frequently exposed to hypoxia and/or ischemia-reperfusion events, suggesting that HO and endogenous CO afford an evolutionary advantage for hypoxia tolerance and are critical in cell survival and injury avoidance. Our goal is to describe the importance of examining HO and CO in several systems, the physiological links, and the genetic factors that underlie variation in the HO/CO pathway. Finally, we emphasize the ways in which evolutionary perspectives may enhance our understanding of the HO/CO pathway in the context of diverse clinical settings.