Fig 2: Expression of pan-neuronal marker PGP9.5 (green) is unchanged between chow, sham, and RYGB groups, as demonstrated by images showing consistent neuronal expression surrounding mucosal crypts (A). Quantification of PGP9.5 immunoreactivity (IR) in colonic mucosa showed no difference in the number of positive pixels between the three groups (B). GLP-1 receptor expression was found in close apposition to the basal end of colonocytes (red), and quantification of pixels showed no change in IR between the groups. N = 5–7. The error bars show SEM, and the scale bar = 10 µm.

Fig 3: Fasting glucose level and incretin system in mice after administration of TNBS (2,4,6-trinitrobenzenesulfonic acid). Intracolonic injection of TNBS resulted in a significant increase in fasting glucose level (A). Glucagon-like peptide 1 (GLP-1) levels were reduced after administration of TNBS in serum (B) and colon samples (D). Dipeptidyl peptidase IV (DPP IV) levels were significantly increased in serum (C), but not in colon samples (E) in mice. Significant increase in prohormone convertase 1/3 (PC1/3) (F) and non-significant in Glucagon-like peptide 1 receptor (GLP-1R) (G) expression was observed in TNBS-treated mice in comparison to controls. *p < 0.05, **p < 0.01, ***p < 0.001. Results are expressed as mean ± SEM for n = 12 mice per group. Comparison between groups were performed using Student’s t test. Data of GLP-1 and DPP IV in colon samples were presented as pg or ng, respectively, per mg of colon tissue. Expression of PC1/3 and GLP-1R was calculated relative to GAPDH. OD—optical density

Fig 4: Impact of Crohn’s diseases (CD) on fasting glucose level and incretin system in human subjects. No significant difference in fasting glucose level was observed (A). Significantly decreased levels of glucagon-like peptide 1 (GLP-1) (B) and dipeptidyl peptidase IV (DPP IV) (C) in CD patients’ serum as compared to healthy controls. No differences in GLP-1 (D) and DPP IV (E) levels in colon samples of CD patients as compared to controls. Moreover, no differences in mRNA levels of prohormone convertase 1/3 (PC 1/3) (F) and glucagon (GCG) (G) and were observed between groups. *p < 0.05 **p < 0.01. Results are expressed as mean ± SEM for n = 11–15 subjects per group for serum samples and n = 5–6 per group for colon samples. Comparison between groups were performed using Student’s t test (or non-parametric Mann–Whitney U test). Data of GLP-1 and DPP IV in colon samples were presented as pg or ng, respectively, per mg of colon tissue. The expression of evaluated genes was normalized to expression of housekeeping gene hypoxanthine–guanine phosphoribosyltransferase (HPRT)