Bovine glycomacropeptide ameliorates experimental rat ileitis by mechanisms involving downregulation of interleukin 17

Abstract

Background and purpose: Bovine glycomacropeptide (BGMP) is an inexpensive, non-toxic milk peptide with anti-inflammatory effects in rat experimental colitis but its mechanism of action is unclear. It is also unknown whether BGMP can ameliorate inflammation in proximal regions of the intestine. Our aim was therefore two-fold: first, to determine the anti-inflammatory activity of BGMP in the ileum; second, to characterise its mechanism of action.

Experimental approach: We used a model of ileitis induced by trinitrobenzenesulphonic acid in rats. Rats were treated orally with BGMP and its efficacy compared with that of oral 5-aminosalicylic acid or vehicle, starting 2 days before ileitis induction.

Key results: BGMP pretreatment (500 mg kg(-1) day(-1)) resulted in marked reduction of inflammatory injury, as assessed by lower extension of necrosis and damage score, myeloperoxidase, alkaline phosphatase, inducible nitric oxide synthase, interleukin 1beta, tumour necrosis factor and interleukin 17. These effects were generally comparable to those of 5-aminosalicylic acid (200 mg kg(-1) day(-1)). Neither compound affected the production of interferon gamma, tumour necrosis factor and interleukin 2 by mesenteric lymph node cells isolated from animals with ileitis. The expression of Foxp3 was increased in ileitis and not reduced significantly by BGMP or aminosalicylate treatment.

Conclusions and implications: These results demonstrate that BGMP has anti-inflammatory activity in the ileum with similar efficacy to 5-aminosalicylic acid. The mechanism of action may involve Th17 and regulatory T cells and perhaps macrophages but probably not Th1 lymphocytes. Patients with Crohn's ileitis may benefit from treatment with BGMP.

Figure 1

Effect of BGMP (bovine glycomacropeptide) on ileal AP (alkaline phosphatase) and myeloperoxidase (MPO) activity. (a) Ileal AP activity. (b) AP sensitivity to the inhibitor levamisole (1 mM). (c) Ileal MPO activity. Values are means±s.e.m, n=6–8. ⁺P<0.05 vs control (C) group; ^*P<0.05 vs trinitrobenzenesulphonic acid group.

Figure 2

Effect of bovine glycomacropeptide on COX2, inducible nitric oxide synthase and Foxp3 protein levels. Ileal samples were analysed by western blot and quantitated with Scion Image software. Representative blots are shown. Values are means±s.e.m., n=6–8. ⁺P<0.05 vs control (C) group; ^*P<0.05 vs trinitrobenzenesulphonic acid group.

Figure 3

Effect of bovine glycomacropeptide on the ileal mRNA levels of IL (interleukin)-1β, IL-1ra, trefoil factor 3, tumour-necrosis factor and IL-17. mRNA levels were measured by semiquantitative RT-PCR and densitometric analysis with Scion Image software. 18S mRNA was used as reference. Densitometric analysis represents the ratio over the 18S signal. Representative blots are shown. Values are means±s.e.m., n=6–8. ⁺P<0.05 vs control (C) group; ^*P<0.05 vs trinitrobenzenesulphonic acid group.