Lab Anim Res.  2016 Mar;32(1):16-23. 10.5625/lar.2016.32.1.16.

Laxative effects of Liriope platyphylla are tightly correlated with suppression of endoplasmic reticulum stress in loperamide-induced constipation of SD rats

• Kim JE
• Go J
• Sung JE
• Lee HA
• Seo EJ
• Yun WB
• Hwang DY

• KMID: 2312150
• DOI: http://doi.org/10.5625/lar.2016.32.1.16

Abstract

A dysfunction of endoplasmic reticulum (ER) stress response can result in various diseases, including cancer, inflammation, diabetes and neurodegenerative disorders. To investigate whether ER stress response can play an essential role in the induction and treatment of chronic constipation, alterations in the key parameters for ER stress were measured in loperamide (Lop) induced constipation Sprague Dawley (SD) rats treated with aqueous extracts of Liriope platyphylla (AEtLP), which has been shown to have a laxative effect. Symptoms of chronic constipation including alteration of stool parameters and the transverse colon's structure were successfully induced by Lop treatment. Laxative effects such as enhancement of stools parameters, recovery of the mucosa thickness, increased muscle thickness and recovery of flat luminal surface were also observed in the Lop+AEtLP treated group. Furthermore, enhancement of eukaryotic initiation factor 2 alpha (eIF2α) phosphorylation and inositol-requiring enzyme 1 beta (IRE1β) expression, key indicators for ER stress, that were observed in the Lop+vehicle treated group were significantly recovered in the Lop+AEtLP treated group, although the phosphorylation level of c-Jun N-terminal protein kinase (JNK) remained constant. Moreover, alterations in the transcription level of the marker genes X-box binding protein 1 (XBP-1) and growth arrest and DNA damage-inducible protein (GADD34) were similar to those of eIF2α and IRE1β. However, their level was slightly or completely recovered after AEtLP treatment. Overall, this study provides the first evidence that ER stress response may be tightly correlated with chronic constipation induced by Lop treatment, as well as the laxative effects of AEtLP.

Keyword

ER stress; constipation; Liriope platyphylla; eIF2α; loperamide; laxative

MeSH Terms

Animals
Carrier Proteins
Constipation*
DNA
Endoplasmic Reticulum Stress*
Endoplasmic Reticulum*
Eukaryotic Initiation Factor-2
Inflammation
Loperamide
Mucous Membrane
Neurodegenerative Diseases
Phenobarbital
Phosphorylation
Protein Kinases
Rats*
Carrier Proteins
DNA
Eukaryotic Initiation Factor-2
Loperamide
Phenobarbital
Protein Kinases

Figure

• 

  Figure 1 Alteration of the histological structure in transverse colons of Loperamide (Lop)-induced constipated rats. Hematoxylin and eosin (H&E)-stained sections of transverse colons from the No treated group (a and d), Lop+vehicle treated group (b and e) or Lop+Liriope platyphylla (AEtLP) treated group (c and f) were observed at two different magnifications (100× and 400×) using a light microscope. (B) The thickness of the mucosa layer and muscle thickness are presented as graphs. Data represent the mean±SD from three replicates. *P<0.05 compared to the No treated group. #P<0.05 compared to the Lop+vehicle treated group.

• 

  Figure 2 Expression of endoplasmic reticulum (ER) stress marker proteins. The expression levels of eukaryotic initiation factor 2 alpha (eIF2α), p-eIF2α and inositol-requiring enzyme 1 beta (IRE1β) in total proteins were detected with specific antibodies. The glyceraldehyde 3-phosphate dehydrogenase (GAPDH) level is also shown as an endogenous control. The band intensity of these proteins was determined using an imaging densitometer and the relative levels of each protein were calculated based on the intensity of GAPDH protein. Data represent the means±SD from three replicates. *P<0.05 compared to the No treated group. #P<0.05 compared to the Lop+vehicle treated group.

• 

  Figure 3 Transcript levels of ER stress marker genes. The levels of X-box binding protein 1 (XBP-1) and growth arrest and DNA damage-inducible protein (GADD34) transcripts in total mRNA of transverse colons were measured by RT-PCR using specific primers. After the intensity of each band was determined using an imaging densitometer, the relative levels of XBP-1 and GADD34 transcripts were calculated based on the intensity of actin transcripts. Five to six rats per group were assayed in triplicate by RT-PCR assays. Data represent the means±SD of three replicates. *P<0.05 compared to the No treated group. #P<0.05 compared to the Lop+Vehicle treated group.

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