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Disbalance of the duodenal epithelial cell turnover and apoptosis accompanies insensitivity of intestinal redox homeostasis to inhibition of the brain glucose-dependent insulinotropic polypeptide receptors in a rat model of sporadic Alzheimer's disease

Introduction: Gastrointestinal dyshomeostasis is investigated in the context of metabolic dysfunction, systemic, and neuroinflammation in Alzheimer’s disease. Dysfunctional gastrointestinal redox homeostasis and the brain- gut incretin axis have been reported in the rat model of insulin-resistant brain state- driven neurodegeneration induced by intracerebroventricular streptozotocin (STZ-icv). We aimed to assess whether (i) the structural epithelial changes accompany duodenal oxidative stress ; (ii) the brain glucose-dependent insulinotropic polypeptide receptor (GIP-R) regulates redox homeostasis of the duodenum ; and (iii) the STZ- icv brain-gut axis is resistant to pharmacological inhibition of the brain GIP-R. Methods: GIP-R inhibitor [Pro3]-GIP (85 μg/kg) was administered intracerebroventricularly to the control and the STZ-icv rats 1 month after model induction. Thiobarbituric acid reactive substances (TBARSs) were measured in the plasma and duodenum, and the sections were analyzed morphometrically. Caspase-3 expression and activation were assessed by Western blot and multiplex fluorescent signal amplification. Results: Intracerebroventricular [Pro3]-GIP decreased plasma TBARSs in the control and STZ-icv animals and increased duodenal TBARSs in the controls. In the controls, inhibition of brain GIP-R affected duodenal epithelial cells, but not villus structure, while all morphometric parameters were altered in the STZ-icv- treated animals. Morphometric changes in the STZ-icv animals were accompanied by reduced levels of caspase-3. Suppression of brain GIP-R inhibited duodenal caspase-3 activation. Conclusion: Brain GIP-R seems to be involved in the regulation of duodenal redox homeostasis and epithelial cell turnover. Resistance of the brain-gut GIP axis and morphological changes indicative of abnormal epithelial cell turnover accompany duodenal oxidative stress in the STZ-icv rats.

streptozotocin ; Alzheimer’s disease ; intestine ; brain-gut axis ; intestinal barrier ; glucose-dependent insulinotropic polypeptide ; incretin ; oxidative stress ; apoptosis

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