Society: AGA

Background: Gastric dysmotility and gastric slow wave dysrhythmias have been well documented in patients with diabetes. However, little is known on the effect of hyperglycemia on small intestine motility such as intestinal slow waves, due to limited options in measuring its activity. Moreover, food intake and digestion process have been reported to alter the small intestine motility in normal rats, but their roles in that of diabetic rats remains unknown. This study aimed to explore the effect of hyperglycemia on small intestinal myoelectrical activity (IMA) and responses to various meals in diabetic and normal rats.
Methods: IMA was recorded via chronically implanted serosal electrodes in the proximal small intestine in rats with diabetes induced by high-fat diet feeding followed by a low dose of streptozotocin (STZ, 30 mg/kg) and normal rats. The percentage of normal slow wave (% NSW) and dominant frequency (DF) were assessed from IMA under various conditions. Oral glucose tolerance test (OGTT, 20% glucose, 1 g/kg) was performed and blood was collected via the tail vein at baseline and 15, 30, 60, 90, 120, 180 min after glucose administration for the measurement of blood glucose. The correlations of blood glucose with NSW and DF were determined. Regular laboratory chow, high-fat diet, and small or large nutrient liquid meal were used to explore IMA responses to different meals in diabetic and normal rats.
Results: (1) Compared with a postprandial increase in DF in normal rats (40.3±1.4 vs. 42.2±0.7 cycles/min (CPM), vs. Fasting, P=0.001, N=6), diabetic rats showed a blunted postprandial response in DF (39.4±3.7 vs. 39.9±3.1 vs. Fasting, P>0.05, N=8) after a regular chow. However, no difference was found in % NSW between diabetic and normal rats in both fasting and fed states; (2) In the fasting state, % NSW was correlated with the blood glucose level in diabetic rats (r=-0.817, P<0.001, Fig.1a) as well as HbA1C (r=-0.871, P=0.005). After glucose administration, the increase in blood glucose was correlated with a decrease in % NSW (r=-0.647, P<0.001, Fig.1b). (3) % NSW in diabetic rats during the 30-min postprandial state was not altered after a meal, either liquid or solid, regular or high-fat diet, small or large meal, suggesting an absence of gastric-small intestinal reflex.
Conclusions: In type 2 diabetic rats, the regularity of intestinal slow waves is negatively correlated with the blood glucose level in both fasting and fed states. Diabetic rats exhibit a blunted postprandial response in intestinal slow waves compared with normal rats. There seems to be a lack of gastric-small intestinal reflex upon food ingestion in diabetic rats. (This study was supported by an NIH grant, R01DK107754)

Correlation of blood glucose and the percentage of normal slow wave (% NSW)<br /> Fig.a In the fasting state, % NSW was correlated with the blood glucose level in diabetic rats (r=-0.817, P<0.001); Fig.b After glucose administration, the increase in blood glucose was correlated with a decrease in % NSW (r=-0.647, P<0.001).

Correlation of blood glucose and the percentage of normal slow wave (% NSW)
Fig.a In the fasting state, % NSW was correlated with the blood glucose level in diabetic rats (r=-0.817, P<0.001); Fig.b After glucose administration, the increase in blood glucose was correlated with a decrease in % NSW (r=-0.647, P<0.001).

Obesity is associated with elevated intestinal nutrient absorption and excessive accumulation of lipids in the liver, adipose tissue, skeletal muscle, and other organs, which contributes to metabolic diseases such as type 2 diabetes, non-alcoholic fatty liver disease (NAFLD), cardiovascular desease, and certain types of cancer. The effect of obesity on intestinal lipid metabolism is currently unclear. We previously demonstrated that the obese phenotype and its associated insulin resistance and NAFLD were ameliorated in mice deficient in the intestinal hormone neurotensin (NT) by inhibiting small intestinal fat absorption and preserving the activity of AMPK, an enzyme that plays a key role as a master regulator of cellular energy homeostasis. However, how NT/AMPK signaling regulates this process remains unknown. The purpose of the current study was to evaluate the genes related to small intestinal lipid absorption in the context of obesity and the regulation of these genes by NT/AMPK signaling. Methods. NT wild type (WT) (Nt ^+/+) and knockout (KO) (Nt ^-/-) mice, fed standard control diet (CD, 10% kcal from fat) or high fat diet (HFD, 60% kcal from fat) were used. i) Total RNA was isolated from mouse jejunal mucosal scrapings and RNAseq analysis performed to profile gene expression; ii) Jejunal crypts were isolated for 2-D monolayer culture; total RNA or protein was isolated for qPCR and western blot analyses, respectively, to confirm gene or protein expression. Results.RNAseq analysis of female mice fed CD or HFD for 28 weeks showed that genes involved in lipid absortion (Fabp1, Fabp2, Cd36, Alpi, and Plin2) were upregulated (FDR <0.05) in Nt ^+/+ mice fed HFD vs. CD; interestingly, these alterations were not noted in Nt ^-^/- mice fed HFD vs. LFD; qPCR or western blot further confirmed these results. Concurrently, phosphorylation of AMPKa (p-AMPKa) was decreased in HFD-fed Nt^+/+ mice, which was rescued by NT deficiency; consistently, palmitic acid (PA) treatment decreased p-AMPKa and increased FABP1 and FABP2 protein expression. Conclusions. These findings suggest that HFD increases small intestinal lipid absorption by upregulating FABP1 and FABP2 expression. HFD feeding or PA treatment decreases p-AMPKa activity, suggesting that AMPK mediates HFD-upregulated FABP1 and FABP2 expression. NT deficiency preserves AMPK signaling and prevents HFD-upregulated FABP1 and FABP2 levels, thus reducing increased lipid absorption. NT signaling may represent a therapeutic target to inhibit intestinal lipid absorption associated with obesity.

Chi Wang

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