Effects of essential fatty acid deficiency on enterohepatic circulation of bile salts in mice

Abstract

Essential fatty acid (EFA) deficiency in mice has been associated with increased bile production, which is mainly determined by the enterohepatic circulation (EHC) of bile salts. To establish the mechanism underlying the increased bile production, we characterized in detail the EHC of bile salts in EFA-deficient mice using stable isotope technique, without interrupting the normal EHC. Farnesoid X receptor (FXR) has been proposed as an important regulator of bile salt synthesis and homeostasis. In Fxr(-/-) mice we additionally investigated to what extent alterations in bile production during EFA deficiency were FXR dependent. Furthermore, we tested in differentiating Caco-2 cells the effects of EFA deficiency on expression of FXR-target genes relevant for feedback regulation of bile salt synthesis. EFA deficiency-enhanced bile flow and biliary bile salt secretion were associated with elevated bile salt pool size and synthesis rate (+146 and +42%, respectively, P < 0.05), despite increased ileal bile salt reabsorption (+228%, P < 0.05). Cyp7a1 mRNA expression was unaffected in EFA-deficient mice. However, ileal mRNA expression of Fgf15 (inhibitor of bile salt synthesis) was significantly reduced, in agreement with absent inhibition of the hepatic bile salt synthesis. Bile flow and biliary secretion were enhanced to the same extent in EFA-deficient wild-type and Fxr(-/-) mice, indicating contribution of other factors besides FXR in regulation of EHC during EFA deficiency. In vitro experiments show reduced induction of mRNA expression of relevant genes upon chenodeoxycholic acid and a selective FXR agonist GW4064 stimulation in EFA-deficient Caco-2 cells. In conclusion, our data indicate that EFA deficiency is associated with interrupted negative feedback of bile salt synthesis, possibly because of reduced ileal Fgf15 expression.

Effect of Gender and Various Diets on Bile Acid Profile and Related Genes in Mice

“…This is also the first study to report that the only difference between mice fed the lab chow vs AIN-93M purified diet was that hepatic Mrp3 was higher in mice fed the lab chow diet. Previous studies in mice fed a high-fat or EFA-deficient diet reported that these diets inhibit the intestinal Fxr-Fgf15 pathway (Lukovac et al, 2009;Li et al, 2020); however, these results were not repeated in the current study. Reasons for this discrepancy could be due to a relatively short duration of time on the diet.…”

Gut microbiota inhibit Asbt-dependent intestinal bile acid reabsorption via Gata4

“…If synthesis was in fact increased in these mice, along with enhanced intestinal BA reabsorption and decreased fecal excretion, then the BA pool would also continuously expand because of a lack of balance between synthesis and disposal. Previous studies on BA synthesis under different conditions have shown that altered synthesis of BAs is not always correlated with changes in Cyp7a1 mRNA expression [31–33]. In a recent paper on Apobec-1 , an enzyme involved in the production of apolipoprotein B48, Cyp7a1 mRNA expression was decreased by approximately 75% in Apobec-1 −/− mice, while no difference in fecal BA excretion was found [34].…”

Docosahexaenoic Acid and Arachidonic Acid Prevent Essential Fatty Acid Deficiency and Hepatic Steatosis

“…However, these clinical signs are now rarely seen in adults with the wide availability of PN and lipid emulsions containing EFA; therefore, biochemical markers such as T:T ratio and EFA index were derived to identify the development of biochemical EFAD 15 . In animals, clinical evidence of EFAD is often not reported 13 and generally requires a long duration of feeding an EFAD diet and/or feeding beginning early in infancy. In our experiments, adult mice fed fat‐deficient and EFA‐deficient diets exhibited biochemical EFAD with accompanying hepatic steatosis without any clinical signs of EFAD.…”

“…Another marker of EFAD is the EFA index, defined as the (n‐3 + n‐6):(n‐7 + n‐9) ratio. These ratios are widely accepted biochemical markers to diagnose EFAD in animals 7 , 13 , 14 and humans 6 , 15 …”