The protein synthesis inhibitor brusatol normalizes high‐fat diet‐induced glucose intolerance in male C57BL/6 mice: role of translation factor eIF5A hypusination

Abstract

The naturally occurring quassinoid compound brusatol improves the survival of insulin‐producing cells when exposed to the proinflammatory cytokines IL‐1β and IFN‐γ in vitro. The aim of the present study was to investigate whether brusatol also promotes beneficial effects in mice fed a high‐fat diet (HFD), and if so, to study the mechanisms by which brusatol acts. In vivo, we observed that the impaired glucose tolerance of HFD‐fed male C57BL/6 mice was counteracted by a 2 wk treatment with brusatol. Brusatol treatment improved both β‐cell function and peripheral insulin sensitivity of HFD‐fed mice. In vitro, brusatol inhibited β‐cell total protein and proinsulin biosynthesis, with an ED50 of ∼40 nM. In line with this, brusatol blocked cytokine‐induced iNOS protein expression via inhibition of iNOS mRNA translation. Brusatol may have affected protein synthesis, at least in part, via inhibition of eukaryotic initiation factor 5A (eIF5A) hypusination, as eIF5A spermidine association and hypusination in RIN‐5AH cells was reduced in a dose‐ and time‐dependent manner. The eIF5A hypusination inhibitor GC7 promoted a similar effect. Both brusatol and GC7 protected rat RIN‐5AH cells against cytokine‐induced cell death. Brusatol reduced eIF5A hypusination and cytokine‐induced cell death in EndoC‐βHl cells as well. Finally, hypusinated eIF5A was reduced in vivo by brusatol in islet endocrine and endothelial islet cells of mice fed an HFD. The results of the present study suggest that brusatol improves glucose intolerance in mice fed an HFD, possibly by inhibiting protein biosynthesis and eIF5A hypusination.—Turpaev, K., Krizhanovskii, C., Wang, X., Sargsyan, E., Bergsten, P., Welsh, N. The protein synthesis inhibitor brusatol normalizes high‐fat diet‐induced glucose intolerance in male C57BL/6 mice: role of translation factor eIF5A hypusination. FASEB J. 33, 3510–3522 (2019). www.fasebj.org