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Background Lipotoxicity-induced cell death plays a detrimental role in the pathogenesis of metabolic diseases. Ferulic acid, widespread in plant-based food, is a radical scavenger with multiple bioactivities. However, the benefits of ferulic acid against hepatic lipotoxicity are largely unclear. Here, we investigated the protective effect of ferulic acid against palmitate-induced lipotoxicity and clarified its potential mechanisms in AML-12 hepatocytes. Methods AML-12 mouse hepatocytes were exposed to palmitate to mimic lipotoxicity. Different doses (25, 50, and 100 μM) of ferulic acid were added 2 h before palmitate treatment. Cell viability was detected by measuring lactate dehydrogenase release, nuclear staining, and the expression of cleaved-caspase-3. Intracellular reactive oxygen species content and mitochondrial membrane potential were analysed by fluorescent probes. The potential mechanisms were explored by molecular biological methods, including Western blotting and quantitative real-time PCR, and were further verified by siRNA interference. Results Our data showed that ferulic acid significantly inhibited palmitate-induced cell death, rescued mitochondrial membrane potential, reduced reactive oxygen species accumulation, and decreased inflammatory factor activation, including IL-6 and IL-1beta. Ferulic acid significantly stimulated autophagy in hepatocytes, whereas autophagy suppression blocked the protective effect of ferulic acid against lipotoxicity. Ferulic acid-activated autophagy, which was triggered by SIRT1 upregulation, was mechanistically involved in its anti-lipotoxicity effects. SIRT1 silencing blocked most beneficial changes induced by ferulic acid. Conclusions We demonstrated that the phytochemical ferulic acid, which is found in plant-based food, protected against hepatic lipotoxicity, through the SIRT1/autophagy pathway. Increased intake of ferulic acid-enriched food is a potential strategy to prevent and/or improve metabolic diseases with lipotoxicity as a typical pathological feature.

Background d-Tagatose 3-epimerase epimerizes d-fructose to yield d-psicose, which is a rare sugar that exists in small quantities in nature and is difficult to synthesize chemically. We aim to explore potential industrial biocatalysts for commercial-scale manufacture of this rare sugar. A d-tagatose 3-epimerase from Rhodobacter sphaeroides (RsDTE) has recently been identified as a d-tagatose 3-epimerase that can epimerize d-fructose to yield d-psicose with a high conversion rate. Results The purified RsDTE by Ni-affinity chromatography, ionic exchange chromatography and gel filtration forms a tetramer in solution. The maximal activity was in Tris–HCl buffer pH 8.5, and the optimal temperature was at 35 °C. The product, d-psicose, was confirmed using HPLC and NMR. Crystals of RsDTE were obtained using crystal kits and further refined under crystallization conditions such as 10% PEG 8000,0.1 M HEPES pH 7.5, and 8% ethylene glycol at 20 °C using the sitting-drop vapor diffusion method. The RsDTE homology model showed that it possessed the characteristic TIM-barrel fold. Four residues, Glu156, Asp189, Gln215 and Glu250, forms a hydrogen bond network with the active Mn(II) for the hydride transfer reaction. These residues may constitute the catalytic tetrad of RsDTE. The residues around O1, O2 and O3 of the substrates were conserved. However, the binding-site residues are different at O4, O5 and O6. Arg118 formed the unique hydrogen bond with O4 of d-fructose which indicates RsDTE’s preference of d-fructose more than any other family enzymes. Conclusions RsDTE possesses a different metal-binding site. Arg118, forming unique hydrogen bond with O4 of d-fructose, regulates the substrate recognition. The research on d-tagatose 3-epimerase or d-psicose 3-epimerase enzymes attracts enormous commercial interest and would be widely used for rare sugar production in the future. Electronic supplementary material The online version of this article (10.1186/s12934-017-0808-4) contains supplementary material, which is available to authorized users.