Pyrroloquinoline Quinone Regulates Enteric Neurochemical Plasticity of Weaned Rats Challenged With Lipopolysaccharide

Abstract

The enteric nervous system (ENS) is important for the intestinal barrier to defend and regulate inflammation in the intestine. The aim of this study was to investigate the effect of pyrroloquinoline quinone (PQQ) on regulating neuropeptide secretion by ENS neurons of rats challenged with lipopolysaccharide (LPS) to create enteritis. Thirty Sprague Dawley rats were divided into five groups, namely, basal (CTRL), basal plus LPS challenge (LPS), basal with 2.5 mg/kg b.w./day of PQQ plus challenge with LPS (PQQ 2.5), basal with 5.0 mg/kg b.w./day PQQ plus challenge with LPS (PQQ 5), and basal with 10.0 mg/kg b.w./day PQQ plus challenge with LPS (PQQ 10). After treatment with basal diet or PQQ for 14 days, rats were challenged with LPS except for the CTRL group. Rats were euthanized 6 h after the LPS challenge. Rats showed an increased average daily gain in PQQ treatment groups (P < 0.05). Compared with the LPS group, PQQ 5 and PQQ 10 rats showed increased villus height and villus height/crypt depth of jejunum (P < 0.05). In PQQ treatment groups, concentrations of IL-1β and TNF-α in serum and intestine of rats were decreased, and IL-10 concentration was increased in serum compared with the LPS group (P < 0.05). Compared with the LPS group, the concentration of neuropeptide Y (NPY), nerve growth factor (NGF), vasoactive intestinal peptide (VIP), substance P (SP), calcitonin gene-related peptide (CGRP), and brain-derived neurotropic factor (BDNF) in serum were decreased in PQQ treatment groups (P < 0.05). Compared with the LPS group, ileal mRNA levels of BDNF, NPY, and NGF were decreased in PQQ treatment groups (P < 0.05). Jejunal concentrations of SP, CGRP, VIP, BDNF, NPY, and NGF were decreased in PQQ treatment groups compared with the LPS group (P < 0.05). Compared with the LPS group, phosphor-protein kinase B (p-Akt)/Akt levels in jejunum and colon were decreased in PQQ treatment groups (P < 0.05). In conclusion, daily treatment with PQQ improved daily gain, jejunal morphology, immune responses. PQQ-regulated enteric neurochemical plasticity of ENS via the Akt signaling pathway of weaned rats suffering from enteritis.

Keywords: Akt signaling pathway; enteric nervous system; enteritis rats; neurochemical plasticity; pyrroloquinoline quinone.

FIGURE 1

Average daily gain of weaned rats (n = 6). (A) Body weight of rats was recorded with feeding time. (B) Average daily gain(ADG) of rats was evaluated by body weight. CTRL, control treatment; lipopolysaccharide (LPS), control and LPS treatment; pyrroloquinoline quinone (PQQ) 2.5, intragastric administration with 2.5 mg/kg b.w./day PQQ⋅Na₂ treatment; PQQ 5, intragastric administration with 5.0 mg/kg b.w./day PQQ⋅Na₂treatment; PQQ 10, intragastric administration with 10.0 mg/kg b.w./day PQQ⋅Na₂ treatment. *Means significant difference with the CTRL group (P ≤ 0.05); ^#means significant difference with the LPS group (P ≤ 0.05).

FIGURE 2

Jejunal morphology by H and E stains. (A) Control treatment; (B) control and LPStreatment; (C) intragastric administration with 2.5 mg/kg b.w./day PQQ⋅Na₂ treatment; (D) intragastric administration with 5.0 mg/kg b.w./day PQQ⋅Na₂ treatment; and (E) intragastric administration with 10.0 mg/kg b.w./day PQQ⋅Na₂ treatment. Scale bars in pictures are 200 μm.

FIGURE 3

Cytokine level in serum and intestinal segments of weaned rats. (A) IL-1β level in serum (n = 6); (B) IL-6 level in serum (n = 6); (C) IL-10 level in serum (n = 5); (D) TNF-α level in serum (n = 6); (E) IL-1β level in jejunum, ileum and colon (n = 6); and (F) TNF-α level in jejunum, ileum and colon (n = 6). CTRL, control treatment; LPS, control and LPS treatment; PQQ 2.5, intragastric administration with 2.5 mg/kg b.w./day PQQ⋅Na₂ treatment; PQQ 5, intragastric administration with 5.0 mg/kg b.w./day PQQ⋅Na₂ treatment; PQQ 10, intragastric administration with 10.0 mg/kg b.w./day PQQ⋅Na₂ treatment. *Means significant difference with the CTRL group (P ≤ 0.05); ^#means significant difference with the LPS group (P ≤ 0.05).

FIGURE 4

Ileal neuropeptide mRNA expression levels of weaned rats (n = 6). SP, substance P; CGRP, calcitonin gene-related peptide; BDNF, brain-derived neurotropic factor; NPY, neuropeptide Y; NGF, nerve growth factor. CTRL, control treatment; LPS, control and LPS treatment; PQQ 2.5, intragastric administration with 2.5 mg/kg b.w./day PQQ⋅Na₂ treatment; PQQ 5, intragastric administration with 5.0 mg/kg b.w./day PQQ⋅Na₂ treatment; PQQ 10, intragastric administration with 10.0 mg/kg b.w./day PQQ⋅Na₂ treatment. *Means significant difference with the CTRL group (P ≤ 0.05); ^#means significant difference with the LPS group (P ≤ 0.05).

FIGURE 5

Neuropeptide levels in serum of weaned rats. NPY, neuropeptide Y (n = 6); NGF, nerve growth factor (n = 5); VIP, vasoactive intestinal peptide (n = 6); SP, substance P (n = 5); CGRP, calcitonin gene-related peptide (n = 5); BDNF, brain-derived neurotropic factor (n = 5). CTRL, control treatment; LPS, control and LPS treatment; PQQ 2.5, intragastric administration with 2.5 mg/kg b.w./day PQQ⋅Na₂ treatment; PQQ 5, intragastric administration with 5.0 mg/kg b.w./day PQQ⋅Na₂ treatment; PQQ 10, intragastric administration with 10.0 mg/kg b.w./day PQQ⋅Na₂ treatment. *Means significant difference with the CTRL group (P ≤ 0.05); ^#means significant difference with the LPS group (P ≤ 0.05).

FIGURE 6

Immunohistochemical staining of jejunal neurons (n = 6). PGP9.5, protein gene product 9.5; SP, substance P; CGRP, calcitonin gene-related peptide; BDNF, brain-derived neurotropic factor; NPY, neuropeptide Y; NGF, nerve growth factor. CTRL, control treatment; LPS, control and LPS treatment; PQQ 2.5, intragastric administration with 2.5 mg/kg b.w./day PQQ⋅Na₂ treatment; PQQ 5, intragastric administration with 5.0 mg/kg b.w./day PQQ⋅Na₂ treatment; PQQ 10, intragastric administration with 10.0 mg/kg b.w./day PQQ⋅Na₂ treatment. Scale bar = 100 μm.

FIGURE 7

Immunohistochemical staining of colonic neurons (n = 6). PGP9.5, protein gene product 9.5; SP, substance P; CGRP, calcitonin gene-related peptide; BDNF, brain-derived neurotropic factor; NPY, neuropeptide Y; NGF, nerve growth factor. CTRL, control treatment; LPS, control and LPS treatment; PQQ 2.5, intragastric administration with 2.5 mg/kg b.w./day PQQ⋅Na₂ treatment; PQQ 5, intragastric administration with 5.0 mg/kg b.w./day PQQ⋅Na₂ treatment; PQQ 10, intragastric administration with 10.0 mg/kg b.w./day PQQ⋅Na₂ treatment. Scale bar = 100 μm.

FIGURE 8

Abundance of the Akt pathway in jejunal and colonic tissues of weaned rats (n = 6). (A) p-Akt, Akt, and PI3K abundances to β-actin in jejunum; (B) p-Akt, Akt, andPI3K abundances to β-actin in the colon. PI3K, phosphatidylinositol-3 kinase; Akt, protein kinase B; CTRL, control treatment; LPS, control and LPS treatment; PQQ 2.5, intragastric administration with 2.5 mg/kg b.w./day PQQ⋅Na₂ treatment; PQQ 5, intragastric administration with 5.0 mg/kg b.w./day PQQ⋅Na₂ treatment; PQQ 10, intragastric administration with 10.0 mg/kg b.w./day PQQ⋅Na₂ treatment. *Means significant difference with the CTRL group (P ≤ 0.05); ^#means significant difference with the LPS group (P ≤ 0.05).