Poster Presentation 2019 Hunter Cell Biology Meeting

Indole-3-propionate, elevated in plasma by high-fibre diets, reduces oxygen free radicals and induces de novo lipogenesis genes in hepatocytes (#135)

Gabrielle Fusco-Allison 1 2 , Jibran Wali 2 , Yen Chin Koay 1 , John O'Sullivan 1 2 3
  1. Cardiometabolic Research Group, Heart Research Institute, Sydney, NSW, Australia
  2. Charles Perkins Centre, Sydney, NSW, Australia
  3. Royal Prince Alfred Hospital, Sydney, NSW, Australia

Background: Recent research has shown significant health benefits deriving from high dietary-fibre consumption. Compared with native starch, dietary-resistant starch is a highly microbiome-accessible carbohydrate (MAC) that significantly alters the gut microbiome population1,2. Many of the benefits of high-MAC diets have been ascribed to increases in short-chain fatty acids, but they alone have not been able to replicate these benefits3.

Aim: To determine the mediators of salutary effects induced by high-fibre diets.

Methods: C57BL/6J mice were fed either native starch (NS) or resistant starch (RS) for 18 weeks (n=20/group). Plasma metabolomics was performed using HILIC HPLC in positive ion mode, and HILIC-AMIDE HPLC in negative ion mode, paired to a 5500 QTRAP QQQ mass spectrometer.  The cecal microbial community was profiled using the 16S rRNA V4 region (515F – 806R) and sequenced with Illumina MiSeq. AML12 hepatocytes were stimulated with hydrogen peroxide and the effect of IPA on generation of oxygen free radicals was assessed using a DCFDA/H2DCFDA - Cellular ROS Assay Kit. AML12 hepatocytes were cultured with and without IPA for 48 hours and the expression of ACLY, a gene implicated in de novo lipogenesis (DNL), was determined.

Results: There was 22-fold increase in gut microbiome-derived tryptophan metabolite indole-3-propionate (IPA) (P=7.9E-3), which was positively correlated with several gut microbiota including Allobaculum, Bifidobacterium, and Lachnospiraceae; Allobaculum having the most consistently increased abundance of all the IPA-associated taxa across all RS-fed mice. IPA both reduced oxygen free radicals by 2-fold (Figure 1, P-value < 0.0001), and increased ACLY gene expression by 1.5-fold (Figure 2, P-value <0.05) in mouse hepatocytes.

Conclusion: IPA, reported to be a potent scavenger of hydroxyl radical species4,5, was dramatically elevated by 22-fold in mice on a high-fibre diet. It suppressed free radical generation in hepatocytes exposed to hydrogen peroxide, and increased expression of the DNL gene ACLY in hepatocytes. We propose IPA is an important mediator of the effects of high-fibre diets, and warrants more extensive investigation.

  1. Bindels, L. B., Walter, J., and Ramer-Tait, A. E. (2015) Resistant starches for the management of metabolic diseases. Curr Opin Clin Nutr Metab Care 18, 559-565
  2. Fuentes‐Zaragoza, E., Sánchez‐Zapata, E., Sendra, E., Sayas, E., Navarro, C., Fernández‐López, J., and Pérez‐Alvarez, J. A. (2011) Resistant starch as prebiotic: a review. Starch‐Stärke 63, 406-415
  3. Keenan, M. J., Zhou, J., Hegsted, M., Pelkman, C., Durham, H. A., Coulon, D. B., and Martin, R. J. (2015) Role of resistant starch in improving gut health, adiposity, and insulin resistance. Adv Nutr 6, 198-205
  4. Chyan, Y. J., Poeggeler, B., Omar, R. A., Chain, D. G., Frangione, B., Ghiso, J., and Pappolla, M. A. (1999) Potent neuroprotective properties against the Alzheimer beta-amyloid by an endogenous melatonin-related indole structure, indole-3-propionic acid. J. Biol. Chem. 274, 21937–21942.
  5. Karbownik, M., Reiter, R. J., Garcia, J. J., Cabrera, J., Burkhardt, S., Osuna, C., and Lewinski, A. (2001) Indole-3-propionic acid, a melatonin-related molecule, protects hepatic microsomal membranes from iron-induced oxidative damage: relevance to cancer reduction. J. Cell. Biochem. 81, 507–513.