Selenium Requirements in Rats, Mice, Lambs, Chicks and Turkeys Based on Selenoprotein Enzyme Activity and Transcript Level

Abstract

Over the past several years, my lab has conducted a series of studies to evaluate selenium (Se) status and requirements in rats, mice and lambs, all using virtually the same diets. These studies progressed from using glutathione peroxidase (GPX) activity as the primary biomarker, to use of GPX protein and GPX mRNA levels as biomarkers, and recently we expanded to include additional selenoenzyme activities as well as transcript levels for the full selenoproteome. Literature reports of Se requirements of turkeys have consistently indicated that turkeys have a markedly higher Se requirement than mammals (NRC: 0.2 μg Se/g). Thus we evaluated the Se requirements of turkey poults, and in parallel, of chicks. The objective here is to compare resulting requirements and to identify clues to better understand the underlying differences in Se requirements and in Se‐deficiency target tissues. For all studies, animals were fed a basal torula yeast diet (0.005–0.007 μg Se/g) with graded levels of Se supplemented as selenite for 4 weeks (lambs 8 wk). Se response curves result in well‐defined Se‐adequate plateaus for all biomarkers except RBC GPX1 activity. Based on plasma GPX3, liver GPX1, and RBC GPX1 activities, the mammalian minimal dietary Se requirement is uniformly 0.1 μg Se/g, whereas the turkey requirement is clearly 3‐times higher at 0.3 μg Se/g; the chick minimum Se requirement is 0.15 μg Se/g based on plasma GPX3 and GPX1 activities. Liver GPX4 activity is only modestly affected by Se deficiency in rats, but falls to ~10% of plateau levels in mice, chicks and poults. In contrast to selenoenzyme activity biomarkers, requirements based on liver GPX1 mRNA are uniformly 0.04–0.11 μg Se/g for rodents and avians, with GPX1 mRNA in Se deficiency falling more dramatically in rodents vs. avians. GPX4 mRNA is little affected by Se deficiency in rodents but falls to 30% in avians. Other unique species differences include high expression of GPX3 mRNA in avian liver; plasma GPX3 activity in Se deficiency falls to 1–3% of plateau levels in rats, chicks, poults and lambs and but only to 35% in mice. Sigmoidal Se response curves are observed for liver GPX1 activity in rats, chicks, turkeys and lambs, and for plasma GPX3 activity in mice, indicating that Se is preferentially directed to other selenoenzymes and/or tissues under Se‐deficient conditions. No mRNA response curves are markedly sigmoidal. Notably, there are no selenoprotein mRNAs that can be used as biomarkers for supernutritional Se status. These studies demonstrate that the minimum dietary Se requirement of young mammals falls over a narrow range, while the requirement of chicks is slightly higher, and turkey requirements are 3‐times that of mammals. Differences in these biomarker Se response curves may help to understand Se metabolism and targeting of tissues in Se deficiency, and thus help to better characterize Se requirements.Support or Funding InformationUSDA Hatch 233618 and 1004389, Northeast Agricultural Univ NECT‐1207‐02 and 1252‐ NCET‐009, and UW Selenium Nutrition Research Fund