Oral administration of
raffinose, a naturally occurring indigestible
oligosaccharide, has reportedly ameliorated
atopic dermatitis in human subjects although the mechanism is unknown. The present study investigated the effect of dietary
raffinose on
allergen-induced airway
eosinophilia in
ovalbumin-sensitised Brown Norway rats as an atopic disease model. Brown Norway rats were immunised by
subcutaneous injection with
ovalbumin on day 0 and fed either a control diet or the diet supplemented with
raffinose (50 g/kg diet). The rats were exposed to aerosolised
ovalbumin on day 20, and broncho-alveolar lavage fluid was obtained on the next day. The number of eosinophils in the fluid was significantly lower in the rats fed the
raffinose diet than in those fed the control diet. Dietary
raffinose significantly reduced
IL-4 and
IL-5 mRNA levels in lung tissue and tended to lower
ovalbumin-specific Ig E levels. Suppression of
eosinophilia by dietary
raffinose was still observed in caecectomised and
neomycin-administered rats, suggesting little contribution by the colonic bacteria to the effect of
raffinose. Intraperitoneal administration of
raffinose also suppressed
eosinophilia. Significant concentrations of
raffinose were detected in portal venous and abdominal arterial plasma after the intragastric administration of
raffinose. Overall, the findings suggest that dietary
raffinose ameliorates allergic airway
eosinophilia at least partly via post-absorptive mechanisms in Brown Norway rats.