Skatole regulates intestinal epithelial cellular functions through activating aryl hydrocarbon receptors and p38

https://doi.org/10.1016/j.bbrc.2019.01.122Get rights and content

Highlights

  • Skatole elicited AhR-mediated death of intestinal epithelial cells (IEC).

  • Skatole-induced apoptosis caused IEC death.

  • AhR activation does not mediate skatole-induced ERK, p38 and JNK activation.

  • A p38 inhibitor promoted skatole-induced death of IEC.

Abstract

Intestinal bacteria produce skatole (3-methylindole) from tryptophan in dietary proteins and ingesting large quantities of animal protein is associated with increased fecal skatole concentrations. Although possibly associated with disrupted intestinal homeostasis, the influence of skatole on intestinal epithelial cellular function has not been characterized in detail. The present study aimed to determine whether skatole induces intestinal epithelial cell (IEC) dysfunction. We found that skatole dose-dependently caused IEC death and time-dependently induced IEC apoptosis. Since skatole directly interacts with aryl hydrocarbon receptors (AhR), we investigated whether these receptors influence the skatole-induced death of IEC. In addition to increased AhR transcriptional activity induced by skatole, the AhR antagonist CH223191 partially suppressed of skatole-induced IEC death. Extracellular signal-related kinase (ERK), p38 and c-Jun N-terminal kinase (JNK) are mitogen-activated protein kinases (MAPK) induced by skatole. None of them were repressed by CH223191, whereas the p38 inhibitor SB203580 promoted skatole-induced IEC death. These findings together indicated that skatole induces both AhR-dependent activation pathways and the AhR-independent activation of p38, consequently regulating the amount of IEC death. Accumulating evidence indicates that consuming large amounts of animal protein is associated with the pathogenesis and progression of inflammatory bowel diseases (IBD). Thus, intestinal skatole production induced by large amounts of dietary animal protein might be associated via IEC death with intestinal pathologies such as IBD.

Introduction

Accumulating evidence indicates that bacterial metabolites derived from food protein are closely associated with the pathogenesis and progression of diseases. For instance, indoxyl sulfate generated in the liver from indole synthesized from tryptophan in dietary proteins by intestinal flora, accelerates the progression of chronic kidney disease (CKD) [[1], [2], [3], [4], [5], [6], [7], [8], [9], [10]] and it is associated with the onset and development of CKD complications such as atherosclerosis [[11], [12], [13], [14]]. Skatole is a bacterially-derived tryptophan metabolite similar to indole that is produced in the small and large intestines of humans, and fecal skatole concentrations change depending on animal protein intake [15,16]. Fecal skatole concentrations in healthy individuals and those who consume large amounts of animal protein range from 0 to 5 and 80–100 μg/g feces, respectively [15,16]. Therefore, skatole produced by ingesting large amounts of red and processed meat affects both intestinal bacteria and the host.

Skatole is involved in bacterial growth and reproduction [15]. It has bacteriostatic effects on gram-negative enterobacteria [15] and it inhibits the growth and fermentation of Lactobacillus species [15,17]. Therefore, skatole might be a determinant of the composition of intestinal microorganisms and the intestinal microbial ecosystem [15,16]. However, the influence of skatole on host intestinal functions is not well understood although it might have deleterious effects on the functions of the intestinal epithelial mucosa [15,16]. Consequently, the present study aimed to identify the relationship between skatole and the death of intestinal epithelial cells (IEC), which obviously plays an important role in the pathogenesis and progression of intestinal diseases such as inflammatory bowel diseases (IBD).

Section snippets

Materials

Antibodies were obtained from the following suppliers: anti-α-tubulin, Calbiochem (La Jolla, CA, USA); anti-cytochrome P-450 1A1 (CYP1A1), Abcam (Cambridge, MA, USA); anti-phospho-extracellular signal-related kinase 1/2 (ERK1/2; Thr202/Tyr204), anti-phospho-p38 (Thr180/Tyr182), anti-phospho-c-Jun N-terminal kinase (JNK; 183/Tyr185), anti-phospho-c-Jun (Ser73) (D47G9) and anti-rabbit and anti-mouse IgG-HRP-linked antibodies were from Cell Signaling Technology (Danvers, MA, USA). Skatole was from

Skatole induces death of intestinal epithelial cells by inducing apoptosis

We initially analyzed the influence of skatole on IEC. The initial maximal concentration of skatole was 1000 μM, because fecal concentrations are considered to range from 1000 to 1200 μM based on the assumption that human feces comprising 60%–80% moisture contains 100 μg/g skatole. Skatole dose-dependently induced the amount of IEC death because the decision coefficient (R2) was 0.80 between concentration of skatole and cell viability (Fig. 1A). In addition, skatole time-dependently elicited

Discussion

Fig. 4 shows a schematic representation of the present novel findings, namely that the apoptotic death of IEC is induced by skatole and is associated with skatole-induced AhR activation. In contrast, the activation of MAPK such as ERK, p38 and JNK induced by skatole is not mediated by AhR, and only p38 activation attenuated IEC death. Therefore, the balance between the activation of AhR and p38 induced by skatole is important for intestinal dysfunction via apoptotic IEC death.

Although the

Acknowledgments

We thank Norma Foster for help with manuscript preparation. This study was supported by Grants-in-Aid for Scientific Research (B) (Grant Number JP15H03090 and JP18H03178 to H.S.) from the Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japan. The authors are grateful to the Faculty of Life and Environmental Sciences in Shimane University for providing financial support for the publication of this report.

References (33)

  • H. Shimizu et al.

    Stat3 contributes to indoxyl sulfate-induced inflammatory and fibrotic gene expression and cellular senescence

    Am. J. Nephrol.

    (2012)
  • H. Shimizu et al.

    Indoxyl sulfate downregulates renal expression of Klotho through production of ROS and activation of nuclear factor-κB

    Am. J. Nephrol.

    (2011)
  • H. Shimizu et al.

    NF-κB plays an important role in indoxyl sulfate-induced cellular senescence, fibrotic gene expression, and inhibition of proliferation in proximal tubular cells

    Am. J. Physiol. Cell Physiol.

    (2011)
  • H. Shimizu et al.

    Senescence and dysfunction of proximal tubular cells are associated with activated p53 expression by indoxyl sulfate

    Am. J. Physiol. Cell Physiol.

    (2010)
  • Y. Adelibieke et al.

    Indoxyl sulfate counteracts endothelial effects of erythropoietin through suppression of Akt phosphorylation

    Circ. J.

    (2013)
  • Z. Tumur et al.

    Indoxyl sulfate upregulates expression of ICAM-1 and MCP-1 by oxidative stress-induced NF-κB activation

    Am. J. Nephrol.

    (2010)
  • Cited by (42)

    • Skatole: A thin red line between its benefits and toxicity

      2023, Biochimie
      Citation Excerpt :

      The use of another intestinal cell line, Caco-2, which is often used as an in vitro model of a ‘normal’ intestinal phenotype after spontaneous differentiation, demonstrated that incubation with skatole (1000 μM) for 24 h resulted in CYP1A1 protein induction. This induction was reversed with the AhR antagonist CH22319 [102]. Moreover, skatole activated mitogen-activated protein kinases (MAPKs), namely, p38, ERK and JNK (Fig. 2, step 4), and significantly increased apoptosis after 48 and 72 h of incubation (Fig. 2, step 3).

    View all citing articles on Scopus
    View full text