Association of gastric inhibitory polypeptide receptor (GIPR) gene polymorphism with type 2 diabetes mellitus in iranian patients

INTRODUCTION

Gastric inhibitory polypeptide receptor (GIPR) encodes a G-protein coupled receptor for gastric inhibitory polypeptide (GIP), which was demonstrated to stimulate insulin secretion. Relation of GIPR gene variation to impaired insulin response has been suggested in previous studies. However, little information is available regarding GIPR polymorphisms and type 2 diabetes mellitus (T2DM). Hence, the aim of the study was to investigate single nucleotide polymorphisms (SNPs) in the promoter and coding regions of GIPR in Iranian T2DM patients.

MATERIALS AND METHODS

Two hundred subjects including 100 healthy and 100 T2DM patients were recruited in the study. Genotypes and allele frequency of rs34125392, rs4380143 and rs1800437 in the promoter, 5' UTR and coding region of GIPR were investigated by RFLP-PCR and Nested-PCR.

RESULTS

Our finding indicated that rs34125392 genotype distribution was statistically different between T2DM and healthy groups (P = 0.043). In addition, distribution of T/- + -/- versus TT was significantly different between the both groups (P = 0.021). Moreover, rs34125392 T/- genotype increased the risk of T2DM (OR = 2.68, 95%CI = 1.203-5.653, P = 0.015). However, allele frequency and genotype distributions of rs4380143 and rs1800437 were not statistically different between the groups (P > 0.05). Multivariate analysis showed that the tested polymorphisms had no effect on biochemical variables.

CONCLUSION

We concluded that GIPR gene polymorphism is associated with T2DM. In addition; rs34125392 heterozygote genotype may increase the risk of T2DM. More studies with large sample size in other populations are recommended to show the ethnical relation of these polymorphisms to T2DM.

GIPR expression in gastric and duodenal neuroendocrine tumors

BACKGROUND

Compounds targeting somatostatin-receptor-type-2 (SSTR2) are useful for small bowel neuroendocrine tumor (SBNET) and pancreatic neuroendocrine tumor (PNET) imaging and treatment. We recently characterized expression of 13 cell surface receptor genes in SBNETs and PNETs, identifying three drug targets (GIPR, OXTR, and OPRK1). This study set out to characterize expression of this gene panel in the less common neuroendocrine tumors of the stomach and duodenum (gastric and duodenal neuroendocrine tumors [GDNETs]).

METHODS

Primary tumors and adjacent normal tissue were collected at surgery, RNA was extracted, and expression of 13 target genes was determined by quantitative polymerase chain reaction. Expression was normalized to GAPDH and POLR2A internal control genes. Expression relative to normal tissue (ddCT) and absolute expression (dCT) were calculated. Wilcoxon tests compared median expression with false discovery rate correction for multiple comparisons.

RESULTS

Gene expression was similar in two gastric and seven duodenal tumors, and these were analyzed together. Like SBNETs (n = 63) and PNETs (n = 51), GDNETs showed significant overexpression compared with normal tissue of BRS3, GIPR, GRM1, GPR113, OPRK1, and SSTR2 (P < 0.05 for all). Of these, SSTR2 had the highest absolute expression in GDNETs (median dCT 4.0). Absolute expression of BRS3, GRM1, GPR113, and OPRK1 was significantly lower than SSTR2 in GDNETs (P < 0.05 for all), whereas expression of GIPR was similar to SSTR2 (median 4.3, P = 0.4).

CONCLUSIONS

As in SBNETs and PNETs, GIPR shows absolute expression close to SSTR2 but has greater overexpression relative to normal tissue (21.1 versus 3.5-fold overexpression). We conclude that GIPR could provide an improved signal-to-noise ratio for imaging versus SSTR2 and represents a promising novel therapeutic target in GDNETs.