The
anti-inflammatory effect of Citrus kawachiensis peel
powder was examined in a murine model of dextran sodium sulfate
(DSS)-induced colitic mice. In addition to the whole powder, its ethanol
extract rich in polyphenolic compounds and ethanol extraction residue
rich in dietary fibers were used. The whole powder ameliorated the
DSS-induced body weight loss (body weight changes on day 9, Control
108 ± 2, DSS 91 ± 4, DSS+whole peel powder 106 ± 1%, p < 0.05), colon shortening (colon length, Control 5.0
± 0.1, DSS 3.9 ± 0.1, DSS+whole peel powder 4.7 ± 0.1
cm, p < 0.05), increased expression of pro-inflammatory
cytokines (e.g., TNF-α, Control 1.0 ± 0.1, DSS 22.2 ±
5.8, DSS+whole peel powder 4.3 ± 1.5 arbitrary unit, p < 0.05), and decreased expression of colonic tight
junctions (TJs) (e.g., occludin, Control 1.00 ± 0.07, DSS 0.21
± 0.07, DSS+whole peel powder 0.70 ± 0.06 arbitrary unit, p < 0.05). The resolution of abnormalities barring the
decreased expression of zonula occludens-2, junctional adhesion molecule-A,
and claudin-7 by the extraction residue was comparable to that achieved
using the powder (body weight change 107 ± 1%; colon length 4.7
± 0.1 cm; TNF-α 4.1 ± 0.7; occludin 0.58 ± 0.06
arbitrary unit, p < 0.05). The ethanol extract
alone did not have any influence on these abnormalities (body weight
change 94 ± 2%; colon length 4.1 ± 0.1 cm; TNF-α 40.5
± 9.0 arbitrary unit; occludin 0.18 ± 0.02 arbitrary unit, p < 0.05). The powder and ethanol extraction residue,
but not ethanol extract, increased fecal acetic acid concentration
(Control 4.9 ± 0.6, DSS 5.0 ± 0.9, DSS+whole peel powder
8.8 ± 1.8, DSS+ethanol extract 5.3 ± 0.8, DSS+ethanol extraction
residue 12.5 ± 1.1 mmol/L, p < 0.05). Taken
together, DFs in the ethanol extraction residue largely contributed
to the peel powder-mediated reduction of TJ barrier defect and inflammation
in colitic mice.