1. Reviewer #3 (Public Review):

    Using high fat diet (HFD)-fed male mice and a variety of experimental approaches, the authors demonstrated the efficacy of xanthohumol (XN) and tetrahydro-xanthohumol (TXN) in attenuating weight gain and hepatic steatosis independently of calorie intake and identify inhibition of PPARγ as a mechanism. A strength of the study design was the incorporation of the test compounds into isocaloric, ingredient matched high-fat diet (HFD) formations and inclusion of a LFD control group. A weakness of the study, although minor, is that the dose of compound consumed will vary between mice and from day-to-day depending on how much food each animal consumes. The lower dose of XN (LXN, given as 30 mg/kg of diet) was found ineffective compared to the higher dose of XN (HZN, 60 mg/kg of diet) and TXN (30 mg/kg of diet) was most effective in attenuating weight gain and reversing HFD-induced liver steatosis. TXN almost completely suppressed hepatic lipid vacuole accumulation and showed greatest reduction in liver mass relative to body weight. TXN increased fasting plasma triglycerides compared to all other groups, but explanation is uncertain. Fecal excretion of TAG between groups was similar and therefore could not explain the decreased weight gain or improved liver phenotypes in XN- or TXN-treated groups. Whole body energy metabolism suggested that XN and TXN supplemented mice were more physically active then HFD-fed mice. HXN and TXN supplemented mice showed less accumulation of subcutaneous and mesenteric fat mass, but these groups had somewhat higher levels of epididymal fat mass.

    After 16 weeks on diets, RNAseq performed on murine liver tissues. Compared to HFD group, TXN group had 295 differentially expressed genes (DEGs), HXN group had 6 DEGs, and LFD group had 212 DEGs. TXN supplementation upregulated 6 and down regulated 25 KEGG pathways. SVM was used to identify signature genes that significantly differentiated HFD and TXN group transcriptomes. Of 13 identified genes, 8 showed significant, differential hepatic expression between TXN and HFD groups. Of these 8 genes, 3 genes (Ucp2, Cidec, Mogat1) were identified as known target genes of PPARγ with roles in lipid metabolism. qPCR of liver tissues was used to verify these RNAseq results.

    XN or TXN were shown to inhibit murine preadipocyte 3T3-L1 differentiation and adipogenesis and lipid accumulation in a dose dependent manner. In a second dose escalating experiment, TXN or XN were shown to block the ability of rosiglitazone (RGZ), a PPARγ agonist, to promote adipogenesis of 3T3-L1. These data suggested that XN and TXN may interfere or compete with binding of RGZ to the PPARγ receptor. qPCR of 3T3-L1 cells confirmed that TXN or XN could inhibit gene expression of RGZ-induced PPARγ target genes (Cd36, Fabp4, Mogat1, Cidec, Plin4, Fgf21) and further supported the hypothesis that TXN and XN are PPARγ antagonists. To further test this idea the authors performed a competitive PPARγ TR-FRET binding assay and showed that XN and TXN could displace a labelled pan-PPARγ ligand in a dose-dependent manner. Finally, molecular docking experiments confirmed the putative binding pose and position of XN/TXN and estimated the relative binding affinities of various ligands for PPARγ. XN and TXN may serve as scaffolds for the development of more potent therapeutics in structure-activity relationship (SAR) studies. Overall, this work contributes compelling preclinical data to support future clinical investigations to determine dosing, efficacy, and safety of XN and TXN as therapeutics for diet-induced NAFLD.

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  2. Reviewer #2 (Public Review):

    The authors showed that the TNX treatment is able to reduces the liver steatosis. But, a lot of results are contradictory. Fer example, the PPAR-gamma is well known insulin sensitizing and the authors did not show the effect of the ntagonism on PPAR-gamma in insulin and glucose homeostasis. Moreover, more analyzis about the adipose tissue are mandatory, since the inhibition of PPAR-gamma might induce the pro-inflammatory status. Thus, to publish in this outstanding journal it is necessary additional experiments to proof that the PPAr-gamma is the main pathway of beneficial effects of TXN.

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  3. Reviewer #1 (Public Review):

    In this study, Zhang et al. systematically analyze the effect of xanthohumol (XN) and TXN, a xanthohumol derivative, in a model of high-fat diet (HFD) feeding to mice, inducing several pathologies related to the metabolic syndrome. They authors convincingly show that XN and TXN attenuate HFD-induced weight gain, hepatic steatosis and lipid accumulation in adipose tissues. Furthermore, they newly show that XN and TXN bind to the PPARgamma ligand-binding domain pocket and that this inhibitory effect on PPARgamma is at least in part responsible for the observe beneficial effects.

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  4. Evaluation Summary:

    This is a comprehensive study of the effect of xanthohumol and TXN, a xanthohumol derivative, on different pathologies related to the metabolic syndrome. It clearly shows the therapeutic potential of these substances, which has a high translational potential since currently, there are is a lack of effective therapies.

    (This preprint has been reviewed by eLife. We include the public reviews from the reviewers here; the authors also receive private feedback with suggested changes to the manuscript. The reviewers remained anonymous to the authors.)

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