Background: The incretin effect is reduced in type 2 diabetes mellitus (T2DM) patients. Whether the impaired function of the enteropancreatic axis in these patients is due to defective GLP-1 receptor (GLP-1R) expression in extrapancreatic target organs is not known.
Aims and methods: To compare the GLP-1R expression and distribution in gastric mucosa biopsies of patients with (n =22) and without (n =22) T2DM referred for routine esophagogastroduodenoscopies. GLP-1R mRNA levels were estimated by real-time PCR. The intensity of GLP-1R immunostaining, frequency, and types of glandular cells bearing GLP-1R and their glandular distribution in different stomach mucosa regions were evaluated by immunohistochemical morphological semiquantitative and quantitative analysis.
Results: Mean mRNA GLP-1R levels were significantly reduced in patients with T2DM compared with nondiabetic patients (P < .02). Immunohistochemical analysis revealed that the reduced GLP-1R expression in T2DM patients was due to a decreased intensity of immunostaining (P < .01). The number of glandular GLP-1R-bearing cells in both body and antrum mucosa was decreased in T2DM patients. Most notably, the frequency of GLP-1R immunoreactive acid-secreting parietal cells was reduced in the neck area of the gastric principal glands of T2DM patients (P < .01). No correlation was found between the reduced GLP-1R expression and clinical parameters including body mass index, age, glycosylated hemoglobin, and disease duration.
Conclusion: This is the first evidence of reduced GLP-1R expression in gastric glands of T2DM patients. These data demonstrate that the defective function of the incretin axis in T2DM may also result from decreased GLP-1R expression in its extrapancreatic target organs.