Supplemental glutamine to restore glutathione homeostasis in the aging mouse liver

Our society is currently aging, with this we are seeing increasing amounts of age-related diseases (ARDs) with the common underlying pathology of oxidative stress. Level’s of the body’s most abundant antioxidant, glutathione, are known to decrease in aging, and this may partly explain the oxidative stress that often develops. Research has shown that under conditions of stress, glutamine stores are depleted. Due to glutamine being closely tied to glutathione synthesis, I wondered if glutamine supplementation could restore the disrupted glutathione homeostasis observed in aging. Before addressing this question, my first objective was to examine if various glutathione probes solely detect glutathione (Chapter 2). The precursor molecule to glutathione, γ-glutamylcysteine, has been shown to have similar antioxidant capabilities as glutathione. I wondered if many of the common assays used to measure glutathione actually solely detect glutathione, as most are thiol probes. What I saw was that monochlorobimane, monobromobimane and o-pthalaldehyde do not solely detect glutathione, however 5,5′-dithiobis-(2-nitrobenzoic acid) (DTNB) does. The second objective was to examine the effect of supplemental glutamine on glutathione homeostasis in the aging liver (chapter 3). I chose to look at this question in 3 mouse models, wild-type, EndoG+/- and Elovl5+/-, these mouse models represent a normal model, a model with healthier mitochondria, and a model with metabolic abnormalities, respectively. In our wild type mouse model, I saw that glutamine supplementation led to worse metabolic health, decreased total glutathione and GSH/GSSG ratio and increased gene expression of glutathione synthetic enzymes as well as antioxidant enzymes. In EndoG+/- mice, I saw lower fasting blood glucose in the glutamine supplemented mice, increases in GSS gene expression, decreases in SNAT1 protein levels and increases in xCT protein levels. Finally, Elovl5+/- mice showed no metabolic changes, however there was a decrease in the GSH/GSSG ratio and an increase in Gpx4 gene expression and nitrotyrosine protein levels. I concluded that many of the popular glutathione probes do not uniquely detect glutathione. Further, supplemental glutamine decreases glutathione levels in vitro. In middle-aged mice, supplemental glutamine decreases glutathione levels in a wild type model, however mitochondrially healthy and metabolically disrupted mice may be protected.Science, Irving K. Barber Faculty of (Okanagan)Biology, Department of (Okanagan)Graduat