Abstract 667: Ergosterol or Brassicasterol Accumulations in ABCG8 Knockout Mice Do Not Account for Xenosterol Toxicity

Abstract

Xenosterol accumulation mice deficient in sterolin function leads to significant toxicity, with infertility, decreased body fat accumulation, macrothrombocytopenia, cardiac fibrosis and premature death1,2. Although sitosterol has been shown to have some biological effect in tissue culture, only stigmasterol has been shown to have a potent biological effect, by activating the transcriptional factor, Lxr3. In patients with sitosterolemia, feeding shell-fish sterols led to accumulation of shell-fish sterols in their plasma4, suggesting any xenosterol could accumulate, if fed, to mammals deficient in Abcg5 or Abcg8. Fungi do not utilize cholesterol, but instead use ergosterol as the primary membrane sterol. To delineate whether ergosterol could accumulate in Abcg8 knockout mice, and lead to toxicity, we designed a diet that was supplemented with highly enriched ergosterol (>98% purity) and fed this to Abcg8 knockout mice. Over a 12-week period, both male and female Abcg8 knockout mice fed an ergosterol-enriched diet gained normal amounts of weight, body fat, showed no disturbances in tail-cuff measured blood pressure, and showed no abnormalities of platelet counts or volumes, blood glucose, or plasma cholesterol. Fertility testing showed no abnormalities. Dramatically, analyses of plasma from these mice showed no accumulation of ergosterol, but a dramatic increase in plasma brassicasterol, with levels reaching 80mg/dL in plasma. Gene expression analyses of livers did not show any consistent patterns, although Lxr target genes were not up-regulated. These data do not support the concept that brassicasterol accumulation, at levels of 80mg/dL in plasma, account for the xenosterol-mediated toxicity observed. Additionally, the intestine shows powerful 1st pass detoxification of ergosterol by converting it to brassicaterol by using (presumably) dehydrocholesterol Δ7 reductase enzyme and highlights the importance of intermediary metabolism enzymes as part of the defense against xenosterols. 1. McDaniel, A.L.et al Am J Pathol, 2013. 182(4): p. 1131-8. 2. Solca, C. et al J Lipid Res, 2013. 54(2): p. 397-409. 3. Yang, C.et al J. Clin. Invest., 2004. 114(6): p. 813-22. 4. Gregg, R.E.et al J. Clin. Invest., 1986. 77(6): p. 1864-72.