Insulin Sensitivity Is Retained in Mice with Endothelial Loss of Carcinoembryonic Antigen Cell Adhesion Molecule 1

CEACAM1 regulates endothelial barrier integrity. Because insulin signaling in extrahepatic target tissues is regulated by insulin transport through the endothelium, we aimed at investigating the metabolic role of endothelial CEACAM1. To this end, we generated endothelial cell-specific Ceacam1 null mice (VECadCre+Cc1fl/fl) and carried out their metabolic phenotyping and mechanistic analysis by comparison to littermate controls. Hyperinsulinemic-euglycemic clamp analysis showed intact insulin sensitivity in VECadCre+Cc1fl/fl mice. This was associated with the absence of visceral obesity and lipolysis and normal levels of circulating non-esterified fatty acids, leptin, and adiponectin. Whereas the loss of endothelial Ceacam1 did not affect insulin-stimulated receptor phosphorylation, it reduced IRS-1/Akt/eNOS activation to lower nitric oxide production resulting from limited SHP2 sequestration. It also reduced Shc sequestration to activate NF-κB and increase the transcription of matrix metalloproteases, ultimately inducing plasma IL-6 and TNFα levels. Loss of endothelial Ceacam1 also induced the expression of the anti-inflammatory CEACAM1-4L variant in M2 macrophages in white adipose tissue. Together, this could cause endothelial barrier dysfunction and facilitate insulin transport, sustaining normal glucose homeostasis and retaining fat accumulation in adipocytes. The data assign a significant role for endothelial cell CEACAM1 in maintaining insulin sensitivity in peripheral extrahepatic target tissues.

Gastrointestinal Region Specific Insulin Permeation Enhancement by Aloe vera Gel

Background: The oral administration route is still the most preferred by patients for drug treatment, but is unfortunately not suitable for all drug compounds. For example, protein and peptide drugs (e.g. insulin) are typically administered via injection seeing as they are unstable in the gastrointestinal luminal environment and have poor membrane permeation properties. To overcome this problem, functional excipients such as drug absorption enhancers can be co-administered. Although Aloe vera gel has the ability to improve the permeation of drugs across the intestinal epithelium, its drug permeation enhancing effect has not been investigated in the different regions of the gastrointestinal tract yet. Objective: The aim of this study was to investigate the insulin permeation enhancing effects of A. vera gel material across excised pig intestinal tissues from different regions of the gastrointestinal tract and to identify the gastrointestinal region where the highest insulin permeation enhancement was achieved. : Insulin transport across excised pig intestinal tissues from the duodenum, proximal jejunum, medial jejunum, distal jejunum, ileum and colon was measured in the absence and presence of A. vera gel (0.5% w/v) using both the Sweetana-Grass diffusion chamber and everted sac techniques. Results: The insulin permeation results obtained from both ex vivo techniques showed varied permeation enhancing effects of A. vera gel as a function of the different regions of the gastrointestinal tract. The colon was identified as the gastrointestinal region where A. vera gel was the most effective in terms of insulin permeation enhancement in the Sweetana-Grass diffusion chamber technique with a Papp value of 5.50 x 10-7 cm.s-1, whereas the ileum was the region where the highest permeation enhancement occurred in the everted sac technique with a Papp value of 5.45 x 10-7 cm.s-1. Conclusion: The gastrointestinal permeation enhancing effects of A. vera gel on insulin is region specific with the highest effect observed in the ileum and colon.

Trans-Endothelial Insulin Transport is Impaired in Skeletal Muscle Capillaries of Obese Male Mice

ABSTRACTDelivery of insulin to the surface of myocytes is required for skeletal muscle (SkM) insulin action. Previous studies have shown that SkM insulin delivery is reduced in the setting of obesity and insulin resistance (IR). The key variables that control SkM insulin delivery are 1) microvascular perfusion and 2) the rate at which insulin moves across the continuous endothelium of SkM capillaries. Obesity and IR are associated with reduced insulin-stimulated SkM perfusion. Whether an impairment in trans-endothelial insulin transport (EIT) contributes to SkM IR, however, is unknown. We hypothesized that EIT would be delayed in a mouse model of diet-induced obesity (DIO) and IR. Using intravital insulin imaging, we found that DIO male mice have a ~15% reduction in EIT compared to their lean counterparts. This impairment in EIT is associated with a 45% reduction in the density of endothelial vesicles. Despite impaired EIT, hyperinsulinemia sustained delivery of insulin to the interstitial space in DIO male mice. Even with maintained interstitial insulin delivery DIO male mice still showed SkM IR, indicating severe myocyellular IR in this model. Interestingly, there was no difference in EIT, endothelial ultrastructure or SkM insulin sensitivity between lean and high fat diet-fed female mice. These results suggest that, in male mice, obesity results in damage to the capillary endothelium which limits the capacity for EIT.