Bacterial metabolism rescues the inhibition of intestinal drug absorption by food and drug additives

Proc Natl Acad Sci U S A. 2020 Jul 7;117(27):16009-16018. doi: 10.1073/pnas.1920483117. Epub 2020 Jun 22.


Food and drug products contain diverse and abundant small-molecule additives (excipients) with unclear impacts on human physiology, drug safety, and response. Here, we evaluate their potential impact on intestinal drug absorption. By screening 136 unique compounds for inhibition of the key intestinal transporter OATP2B1 we identified and validated 24 potent OATP2B1 inhibitors, characterized by higher molecular weight and hydrophobicity compared to poor or noninhibitors. OATP2B1 inhibitors were also enriched for dyes, including 8 azo (R-N=N-R') dyes. Pharmacokinetic studies in mice confirmed that FD&C Red No. 40, a common azo dye excipient and a potent inhibitor of OATP2B1, decreased the plasma level of the OATP2B1 substrate fexofenadine, suggesting that FD&C Red No. 40 has the potential to block drug absorption through OATP2B1 inhibition in vivo. However, the gut microbiomes of multiple unrelated healthy individuals as well as diverse human gut bacterial isolates were capable of inactivating the identified azo dye excipients, producing metabolites that no longer inhibit OATP2B1 transport. These results support a beneficial role for the microbiome in limiting the unintended effects of food and drug additives in the intestine and provide a framework for the data-driven selection of excipients. Furthermore, the ubiquity and genetic diversity of gut bacterial azoreductases coupled to experiments in conventionally raised and gnotobiotic mice suggest that variations in gut microbial community structure may be less important to consider relative to the high concentrations of azo dyes in food products, which have the potential to saturate gut bacterial enzymatic activity.

Keywords: azoreductases; drug absorption; excipients; food additives; human gut microbiome.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • ATP Binding Cassette Transporter, Subfamily B / genetics
  • ATP-Binding Cassette Sub-Family B Member 4
  • Animals
  • Anti-Allergic Agents / metabolism
  • Anti-Allergic Agents / pharmacokinetics
  • Azo Compounds
  • Bacteria / isolation & purification
  • Bacteria / metabolism*
  • Excipients / metabolism*
  • Excipients / pharmacokinetics
  • Female
  • Food Additives / metabolism*
  • Food Additives / pharmacokinetics
  • Food*
  • Gastrointestinal Microbiome / physiology*
  • Histamine H1 Antagonists, Non-Sedating / metabolism
  • Histamine H1 Antagonists, Non-Sedating / pharmacokinetics
  • Humans
  • Intestinal Absorption / drug effects
  • Intestinal Absorption / physiology*
  • Male
  • Mice
  • Mice, Inbred BALB C
  • Mice, Knockout
  • Organic Anion Transporters / metabolism*
  • Terfenadine / analogs & derivatives


  • ATP Binding Cassette Transporter, Subfamily B
  • Anti-Allergic Agents
  • Azo Compounds
  • Excipients
  • Food Additives
  • Histamine H1 Antagonists, Non-Sedating
  • Organic Anion Transporters
  • SLCO2B1 protein, human
  • Slco2b1 protein, mouse
  • Terfenadine
  • multidrug resistance protein 3
  • fexofenadine