Circulating glutathione concentrations in marine, semiaquatic, and terrestrial mammals

Abstract

An important low molecular weight antioxidant in biological systems is glutathione; its efficiency depends on the equilibrium between its reduced (GSH) and oxidized (GSSG) forms. The oxidized:total glutathione (GSSG:GSH‐Eq) ratio can be used as an indicator of oxidative stress. Previous studies suggest that marine mammals, unlike terrestrial mammals, do not show adverse effects in tissues exposed to ischemia/reperfusion during the peripheral vasoconstriction associated with breath‐hold diving. This is due, in part, to higher antioxidant enzyme activities in marine mammals compared with terrestrial mammals. The objective of this study was to compare circulating glutathione levels among mammals with different diving capacities. Circulating GSH‐Eq, GSH, and GSSG concentrations in erythrocyte samples from northern elephant seals (Mirounga angustirostris), bottlenose dolphins (Tursiops truncatus), neotropical otters (Lontra longicaudis annectens), domestic pigs (Sus scrofa), and humans were quantified using spectrophotometry. Higher GSH‐Eq and GSH concentrations and a lower GSSG:GSH‐Eq index were found in erythrocytes from northern elephant seals and bottlenose dolphins as compared to otters, domestic pigs, and humans. Results suggest that marine mammals, independent of their diving capacity, possess a highly developed antioxidant system, including GSH; continuous availability of GSH could allow these species to avoid oxidative damage and tolerate ischemia/reperfusion and hypoxia/reoxygenation events associated with diving.

Natural Tolerance to Ischemia and Hypoxemia in Diving Mammals: A Review

“…Baseline circulating and tissue antioxidant levels are higher in diving versus non-diving birds and mammals, supporting the hypothesis that a robust antioxidant defense system mitigates injury from diving-induced oxidant generation in marine vertebrates (Corsolini et al, 2001; Wilhelm Filho et al, 2002; Vázquez-Medina et al, 2006, 2007, 2012; Zenteno-Savin et al, 2010, 2011; García-Castañeda et al, 2017). Whether this relationship between antioxidant levels and diving capacity holds across diving species remains unclear; interspecies comparisons of diving capacity and antioxidant levels are difficult to isolate from confounding species-specific life history factors such as fasting and maturation (Cantú-Medellín et al, 2011; Righetti et al, 2014; Colominas-Ciuró et al, 2017; García-Castañeda et al, 2017). However, in phocid seals, the antioxidant system develops alongside diving capacity during postnatal maturation and does not decline with aging, suggesting a link between diving ability and antioxidant defenses (Vázquez-Medina et al, 2011b,c; Allen et al, 2019).…”

“…High activity and expression of antioxidant enzymes, particularly those related to the glutathione system, have been observed across diving birds and mammals (Murphy and Hochachka, 1981; Corsolini et al, 2001; Wilhelm Filho et al, 2002; Vázquez-Medina et al, 2006, 2007; Zenteno-Savin et al, 2010; García-Castañeda et al, 2017). Baseline circulating and tissue antioxidant levels are higher in diving versus non-diving birds and mammals, supporting the hypothesis that a robust antioxidant defense system mitigates injury from diving-induced oxidant generation in marine vertebrates (Corsolini et al, 2001; Wilhelm Filho et al, 2002; Vázquez-Medina et al, 2006, 2007, 2012; Zenteno-Savin et al, 2010, 2011; García-Castañeda et al, 2017). Whether this relationship between antioxidant levels and diving capacity holds across diving species remains unclear; interspecies comparisons of diving capacity and antioxidant levels are difficult to isolate from confounding species-specific life history factors such as fasting and maturation (Cantú-Medellín et al, 2011; Righetti et al, 2014; Colominas-Ciuró et al, 2017; García-Castañeda et al, 2017).…”

Contraction of the ROS Scavenging Enzyme GlutathioneS-Transferase Gene Family in Cetaceans

“…Oxidative damage is limited in cetaceans due to an intrinsic protection against ROS by scavenging enzymes and nonenzymatic antioxidants. Ceteceans have increased blood levels of the reduced form of glutathione (GSH), one of the most important nonenzymatic ROS scavengers (Wilhelm Filho et al 2002; García-Castañeda et al 2017). Similarily, the blood levels of vitamin E (α-tocopherol), which acts as a nonenzymatic antioxidant by protecting against peroxidation (Niwa 1999), is elevated in bottlenose dolphins ( Tursiops truncatus ) compared to its terrestrial sister taxa (Kasamatsu et al 2009).…”

Parental dietary sucrose affects metabolic and antioxidant enzyme activities in Drosophila

“…They can supply reductive equivalents in the form of glutathione (GSH) and NADPH. The reduced form of GSH, a thiol-containing compound, is one of the most important low-molecular-weight ROS scavengers (García-Castañeda et al 2017). Glutathione-Stransferase catalyzes the conjugation of metabolites, xenobiotics and endogenous or exogenous electrophilic compounds with the thiol group of reduced GSH to render them less toxic, more soluble and easier to excrete from cells (Enayati et al 2005;Ketterman et al 2011).…”