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Hepatic De Novo Lipogenesis Is Suppressed and Fat Oxidation Is Increased by Omega-3 Fatty Acids at the Expense of Glucose Metabolism

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Hepatic De Novo Lipogenesis Is Suppressed and Fat Oxidation Is Increased by Omega-3 Fatty Acids at the Expense of Glucose Metabolism Metabolism BMJ Open Diab Res Care: first published as 10.1136/bmjdrc-2019-000871 on 17 March 2020. Downloaded from Open access Original research Hepatic de novo lipogenesis is suppressed and fat oxidation is increased by omega-3 fatty acids at the expense of glucose metabolism Charlotte J Green,1 Camilla Pramfalk,1 Catriona A Charlton,1 Pippa J Gunn,1 Thomas Cornfield,1 Michael Pavlides,1,2 Fredrik Karpe ,1,3 Leanne Hodson 1,3 To cite: Green CJ, Pramfalk C, ABSTRACT Charlton CA, et al. Hepatic Objective Increased hepatic de novo lipogenesis (DNL) is Significance of this study de novo lipogenesis is suggested to be an underlying cause in the development suppressed and fat oxidation of nonalcoholic fatty liver disease and/or insulin resistance. What is already known about this subject? is increased by omega-3 It is suggested that omega-3 fatty acids (FA) lower ► Supplementation with the marine- derived omega-3 fatty acids at the expense fatty acids, eicosapentaenoic acid and docosahex- of glucose metabolism. hepatic DNL. We investigated the effects of omega-3 FA supplementation on hepatic DNL and FA oxidation using a aenoic acid, significantly decrease plasma triacyl- BMJ Open Diab Res Care glycerol concentrations and may reduce intrahepatic 2020;8:e000871. doi:10.1136/ combination of human in vivo and in vitro studies. triacylglycerol content. bmjdrc-2019-000871 Research design and methods Thirty-eight healthy men were randomized to take either an omega-3 supplement ► Animal and in vitro cellular studies have shown that (4 g/day eicosapentaenoic acid (EPA)+docosahexaenoic omega-3 fatty acids have a hepatocyte-specific ► Additional material is acid (DHA) as ethyl esters) or placebo (4 g/day olive effect at the level of gene transcription where they published online only. To view oil) and fasting measurements were made at baseline co- ordinately downregulate hepatic lipogenesis and please visit the journal online and 8 weeks. The metabolic effects of omega-3 FAs on upregulate fatty acid oxidation. (http:// dx. doi. org/ 10. 1136/ intrahepatocellular triacylglycerol (IHTAG) content, hepatic bmjdrc- 2019- 000871). What are the new findings? DNL and FA oxidation were investigated using metabolic ► Supplementation with omega-3 fatty acids in hu- substrates labeled with stable-isotope tracers. In vitro mans downregulated fasting and postprandial CJG and CP contributed equally. studies, using a human liver cell-line was undertaken to hepatic de novo lipogenesis and increased post- gain insight into the intrahepatocellular effects of omega-3 prandial fatty acid oxidation. Received 31 August 2019 FAs. We found fasting and postprandial plasma glucose Revised 7 February 2020 Results Fasting plasma TAG concentrations significantly ► Accepted 20 February 2020 concentrations increased after supplementation decreased in the omega-3 group and remained http://drc.bmj.com/ with omega-3 fatty acids. unchanged in the placebo group. Eight weeks of omega-3 supplementation significantly decreased IHTAG, fasting How might these results change the focus of and postprandial hepatic DNL while significantly increasing research or clinical practice? dietary FA oxidation and fasting and postprandial plasma ► When hepatic de novo lipogenesis is attenuated, glucose concentrations. In vitro studies supported the consideration needs to be given to the impact ex- in vivo findings of omega-3 FAs (EPA+DHA) decreasing cess nonlipid substrates may have on other meta- intracellular TAG through a shift in cellular metabolism bolic pathways. on September 28, 2021 by guest. Protected copyright. away from FA esterification toward oxidation. © Author(s) (or their ► Understanding how omega-3 fatty acid supplemen- Conclusions Omega-3 supplementation had a potent employer(s)) 2020. Re- use tation may affect hepatic glucose metabolism in hu- permitted under CC BY. effect on decreasing hepatic DNL and increasing FA mans in vivo remains to be determined. Published by BMJ. oxidation and plasma glucose concentrations. Attenuation Clarifying the impact background diet has on met- 1 of hepatic DNL may be considered advantageous; however, ► University of Oxford, Oxford, abolic pathways when humans are supplemented UK consideration is required as to what the potential excess of 2 with omega-3 fatty acids. Translational Gastroenterology nonlipid substrates (eg, glucose) will have on intrahepatic Unit, John Radcliffe Hospital, and extrahepatic metabolic pathways. Oxford, UK Trial registration number NCT01936779. 3 National Institute for Health 1 Research Oxford Biomedical 2 diabetes (T2D). Increased hepatic de Research Centre, Oxford novo lipogenesis (DNL) is often suggested University Hospitals Foundation INTRODUCTION to be an underlying cause in the develop- Trust, Oxford, UK Nonalcoholic fatty liver disease (NAFLD), ment of NAFLD and/or insulin resistance.2 defined as excess intrahepatocellular tria- Observational studies have reported fasting Correspondence to Professor Leanne Hodson; cylglycerol (IHTAG) accumulation due to hepatic DNL to be higher in individuals with 3 4 leanne. hodson@ ocdem. ox. nonalcoholic causes, is a complication in NAFLD compared with those without. It ac. uk individuals who are obese and/or have type has been suggested that changes in plasma BMJ Open Diab Res Care 2020;8:e000871. doi:10.1136/bmjdrc-2019-000871 1 BMJ Open Diab Res Care: first published as 10.1136/bmjdrc-2019-000871 on 17 March 2020. Downloaded from Metabolism TAG concentrations are proportional to the amount of were studied before and 8 weeks after supplementation hepatic DNL.5 (online supplementary figure 1). Participants random- Supplementation with the marine-derived omega-3 ized to the omega-3 FA group consumed 4×1 g capsules/ fatty acids (FAs), eicosapentaenoic acid (EPA) and doco- day with each capsule containing 460 mg EPA ethyl ester sahexaenoic acid (DHA), in doses of ≥3 g/day signifi- and 380 mg DHA ethyl ester (a total of 1.84 g EPA+1.52 g cantly decrease plasma TAG concentrations6 and can DHA/day (medicinal product name Omacor/Lovaza)). reduce IHTAG content.7 In vitro cellular and animal Participants randomized to the placebo group consumed models have proposed the mechanisms by which this is 4×1 g capsules/day with each capsule containing olive oil achieved include downregulation of lipogenic and upreg- (FA composition oleic acid ~67%, palmitic acid ~15%, ulation of β-oxidation pathways via hepatic transcription linoleic acid ~15% and stearic acid ~2%, alpha linolenic factors.7 In- line with omega-3 FAs upregulating β-oxida- acid ~1%). This was an open- label study and the dose tion, some,8 9 but not all,10 have reported an increase of 4 g/day was based on previous studies16 17 and olive in fat oxidation, when assessed by indirect calorimetry. oil was chosen as a placebo as oleic acid is a commonly However, few have assessed the effect of omega-3 FAs on consumed FA due to its ubiquitous nature in foods18 fasting and postprandial hepatic DNL and FA oxidation, and has been used previously.10 16 17 Both the omega-3 simultaneously, in vivo, in humans. and placebo were administrated as 1 g, soft red- brown, The effects of omega-3 supplementation on markers gelatin shelled capsules and participants were encour- of glycemia are inconsistent. For example, Logan et al8 aged to take the supplement with the first meal of the reported no change in older, overweight/obese females day. Supplements (omega-3 and placebo) were provided taking 3 g EPA+DHA for 12 weeks, while others report by Pronova BioPharma (now part of BASF) (Pronova Bio- increased fasting plasma glucose concentrations in Pharma ASA, Lysaker, Norway). individuals with T2D taking 20 mL fish oil for 9 weeks9 We determined the 90th percentile of plasma TAG 11 or 5 g EPA+DHA for 24 weeks ; in one case, a decrease concentrations for males in the OBB was 2.2 mmol/L was reported in overweight/obese adults with impaired (SD of 0.5 mmol/L). Based on the work of Chan et al,19 20 12 glucose tolerance taking 3 g EPA+DHA for 18 months. who reported a 25% decrease in plasma TAG, in males The disparity in findings is likely related to the dose after 6 weeks of omega-3 FA supplementation (4 g/day and duration of omega-3 supplementation along with EPA+DHA), we predicted a 20% decrease in plasma TAG the clinical status of the individuals studied. In a pilot after 8 weeks supplementation with 4 g/day of omega-3 study, we previously found supplementation with 4 g/day FA. The number of individuals required to detect a 20% EPA+DHA for 15–18 months in individuals with NAFLD decrease in plasma TAG, with a power of 0.80 and α of did not alter fasting plasma glucose concentrations, but 0.05, was n=21. The supplementation period of 8 weeks decreased fasting hepatic DNL and increased plasma was based on the work of Cussons et al.17 13 3- hydroxybutryate (3OHB) concentrations. Therefore, Whole body composition and fat distribution were the aim of this work was to extend our previous observa- measured using dual- energy X- ray absorptiometry21 at tions and investigate the effect of 8 weeks of EPA+DHA the baseline visit. (omega-3) supplementation on fasting and postprandial http://drc.bmj.com/ hepatic DNL and FA oxidation using a combination of Placebo group human in vivo and in vitro models and stable- isotope Of the 23 individuals randomized, 4 did not complete the tracer methodology. study due to changes in personal and/or working circum- stances, therefore giving complete data for 19 individuals (online supplementary figure 1). Participants came in on September 28, 2021 by guest. Protected copyright. RESEARCH DESIGN AND METHODS to the Clinical Research Unit after an overnight fast for In vivo human studies fasting blood samples, at the beginning and 8 weeks after Healthy male participants, with fasting plasma TAG supplementation with placebo capsules.
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