GLP-1 secretion and signaling in patients with aneurysmal enlargement of the thoracic aorta : a potential contributor to reduced prevalence of aneurysm in diabetes

An aortic aneurysm is a localized dilation of the artery, greater than 50% of the normal size. It is the result of a weakening of the aortic wall, and untreated or unrecognized aortic aneurysms may be fatal due to massive internal bleeding, as a result of dissection or rupture of the aneurysm. The aorta is divided into two major sections; the thoracic and the abdominal aorta. Approximately 25% of all aneurysms are Thoracic aortic aneurysms (TAA) and the remaining are Abdominal aortic aneurysms (AAA). Most commonly, TAAs are located in the ascending aorta (AscAA). There are different conditions that involve increased risk of TAA formation, for example, bicuspid aortic valve (BAV), a congenital condition where the aortic valve has two instead of three (tricuspid aortic valve (TAV)) cusps. The mechanisms underlying the increased prevalence of TAA among BAV patients are largely unknown. However, differential mechanisms have been indicated in aneurysm formation in BAV and TAV patients. Interestingly though, the prevalence of AAA and TAA among BAV and TAV patients alike is reduced among those with type 2 diabetes (T2D). The reduced prevalence of TAA in T2D has been speculated to involve pharmacological treatment. The peptide hormone, Glucagon-like peptide-1 (GLP-1) is an intestinal hormone and neuronal peptide with an important role in glucose metabolism, primarily through enhanced glucose-induced insulin secretion, wherefore GLP-1 also forms the basis of current anti-diabetic therapy. Although studies have indicated defective postprandial secretion of GLP-1, T2D is also associated with increased fasting plasma levels of GLP-1. Of note, the GLP-1 receptor is expressed in various different tissues including the vasculature, and GLP-1-based therapy prevents aneurysm formation in vivo. Furthermore, clinical studies indicate that GLP-1 governs many of the mechanisms implicated in TAA formation/progression, such as inflammation, oxidative stress, and proteolytic activity. Smooth muscle cells (SMCs) play a central role in TAA pathology, where the transition from a differentiated (with contractile function) to a de-differentiated (synthetic) phenotype is important in the formation/progression of TAA. Some of the indicated beneficial effects of GLP-1-based therapy on TAA pathology may be speculated to involve the proteoglycan, syndecan-1 (Sdc-1), whose expression is regulated by intracellular targets of the GLP-1 receptor (GLP-1R). Sdc-1 modulates pro-inflammatory processes and has a protective role in aortic aneurysm. Nevertheless, it is not known whether T2D or enhanced fasting plasma GLP-1 in T2D is associated with altered inflammatory profile, proteolytic activity, or Sdc-1 expression, nor are the effects of GLP-1R activation on SMCs in the presence/absence of diabetic conditions well characterized. Our hypothesis was that elevated fasting plasma GLP-1 levels, in T2D patients with valve disease, may contribute to the reduced risk of AscAA in T2D patients. The aim of this project was to further understanding of a potential role for GLP-1 in the reduced prevalence of AscAA in T2D, by assessing potential correlations between elevated fasting plasma GLP-1 and processes involved in aortic aneurysm formation, including inflammation, proteolytic activity, and Sdc-1 expression. In addition, we aimed to determine potential direct effects of GLP-1 signaling on aortic SMCs. In Paper I, we show that patients with T2D are characterized by a shift towards an anti-inflammatory profile, which is associated with elevated fasting plasma GLP-1. Furthermore, a potential role for this anti-inflammatory shift in the reduced prevalence of AscAA in T2D patients is indicated by the inflammatory Th1 bias of immune responses in patients with AscAA. In Paper II, the results show elevated expression of Sdc-1 in the aorta of T2D patients, facilitating a possible role for this increase in T2D- associated reduced prevalence of AscAA. We also demonstrate increased Sdc-1 expression in AscAA patients in association with increased infiltration of macrophages, substantiating data from in vivo studies indicating a role for Sdc-1 upregulation on immune cells as a counterbalancing response to TAA formation. In Paper III, results do not indicate an association between T2D and increased Sdc-1 expression in aortic adventitial tissue among BAV patients. Nor was increased macrophage infiltration or Sdc-1 expression detected in association with AscAA among BAV patients. Finally, in Paper IV, we show that GLP-1R is highly expressed in differentiated aortic SMCs, as compared to de-differentiated SMCs, and its activation attenuates Angiotensin II induced downregulation of Sdc-1 expression. In addition, a diabetic milieu increased the gene expression of the differentiation markers (calponin and myosin). In conclusion, this study indicates that T2D is associated with a Th2 bias, and increased aortic expression of Sdc-1, which may play a role in the reduced prevalence of AscAA in T2D

Minimal shedding of the glycocalyx layer during abdominal hysterectomy

Funding Information: This project was funded by the Stockholm City Council, the Kleberg Foundation and Riga Stradins University. Publisher Copyright: © 2017 The Author(s).Background: Surgery with and without hypervolaemia may cause shedding (breakdown) of the endothelial glycocalyx layer, but the severity of this problem is unclear. Methods: In this preliminary report of a larger clinical trial, the plasma and urine concentrations of three biomarkers of glycocalyx shedding (syndecan-1, hyaluronic acid and heparan sulfate) were measured in seven patients before, during, and after open hysterectomy. The fluid therapy consisted of 25ml/kg (approximately 2l) of Ringer's lactate, which was infused over 30min when the surgery started. The resulting plasma volume expansion at the end of the infusion was estimated from the haemodilution. Results: The mean plasma concentration of syndecan-1 was 21.7ng/ml before surgery and averaged 19.7ng/ml during and after the surgery. The plasma concentration of hyaluronic acid decreased from 38.0 to 27.7ng/ml (P<0.05), while heparan sulfate increased from 3.4 to 5.5μg/ml (P<0.05). The urine concentrations of syndecan-1 decreased significantly, while they increased for hyaluronic acid and heparan sulfate. Despite the vigorous fluid load, the urine flow did not exceed 1ml/min. Conclusions: No clear evidence was found for shedding of the endothelial glycocalyx layer when 2l of Ringer's lactate was infused over 30min during abdominal hysterectomy. Urine analyses yielded patterns of changes that differed from those in plasma. Trial registration:ISRCTN81005631. Registered May 17, 2016.publishersversionPeer reviewe

Elevated Glucagon-like Peptide-1 and a Th2 Shift May Support Reduced Prevalence of Thoracic Aortic Aneurysm in Patients with Diabetes

Glucagon-like peptide-1 (GLP-1) regulates processes involved in the pathophysiology of thoracic aortic aneurysms (TAAs), including inflammation, while protecting against aortic aneurysms in animal models. Type 2 diabetes (T2D) involves altered GLP-1 signaling due to pathology and/or therapy and is associated with reduced prevalence of TAAs. We aimed to assess whether T2D alters the inflammatory profile/proteolytic activity, possible correlations to elevated fasting GLP-1 (F-GLP-1), and its relevance for TAA. F-GLP-1, pro-inflammatory T helper 1 (Th1) cytokines, Th2 cytokines, C-reactive protein, and matrix metalloproteinase-2 activity (MMP-2) were analyzed in surgical patients with aortic valve pathology with/without T2D and without T2D but with TAA. Patients with T2D displayed an increase in the relative systemic expression of interleukin 6 and tumor necrosis factor α and a clear trend towards reduced levels of interferon γ (IFNγ). In addition, a positive association between GLP-1 and the plasma interleukin 4 (IL-4)/IFNγ ratio was detected. TAA was associated with significantly lower plasma levels of the Th2 cytokines IL-4 and interleukin 5. Plasma MMP-2 activity did not differ between groups. We conclude that T2D involved a Th2 shift, which associates with elevated F-GLP-1 and may—considering Th1 bias in TAA—contribute to reduced prevalence of TAA in T2D

Long chain saturated and unsaturated fatty acids exert opposing effects on viability and function of GLP-1-producing cells : Mechanisms of lipotoxicity

Background and aim: Fatty acids acutely stimulate GLP-1 secretion from L-cells in vivo. However, a high fat diet has been shown to reduce the density of L-cells in the mouse intestine and a positive correlation has been indicated between L-cell number and GLP-1 secretion. Thus, the mechanism of fatty acid-stimulated GLP-1 secretion, potential effects of long-term exposure to elevated levels of different fatty acid species, and underlying mechanisms are not fully understood. In the present study, we sought to determine how long-term exposure to saturated (16:0) and unsaturated (18:1) fatty acids, by direct effects on GLP-1-producing cells, alter function and viability, and the underlying mechanisms. Methods: GLP-1-secreting GLUTag cells were cultured in the presence/absence of saturated (16:0) and unsaturated (18:1) fatty acids (0.125 mM for 48 h, followed by analyses of viability and apoptosis, as well as involvement of fatty acid oxidation, free fatty acid receptors (FFAR1) and ceramide synthesis. In addition, effects on the expression of proglucagon, prohormone convertase 1/3 (PC1/3), free fatty acid receptors (FFAR1, FFAR3), sodium glucose cotransporter (SGLT) and subsequent secretory response were determined. Results: Saturated (16:0) and unsaturated (18:1) fatty acids exerted opposing effects on the induction of apoptosis (1.4-fold increase in DNA fragmentation by palmitate and a 0.5-fold reduction by oleate; p&lt;0.01). Palmitate-induced apoptosis was associated with increased ceramide content and co-incubation with Fumonisin B1 abolished this lipo apoptosis. Oleate, on the other hand, reduced ceramide content, and-unlike palmitate-upregulated FFAR1 and FFAR3, evoking a 2-fold increase in FFAR1-mediated GLP-1 secretion following acute exposure to 0.125 mmol/L palmitate; (p&lt;0.05). Conclusion/Interpretation: Saturated (16:0), but not unsaturated (18:1), fatty acids induce ceramide-mediated apoptosis of GLP-1-producing cells. Further, unsaturated fatty acids confer lipoprotection, enhancing viability and function of GLP-1-secreting cells. These data provide potential mechanistic insight contributing to reduced L-cell mass following a high fat diet and differential effects of saturated and unsaturated fatty acids on GLP-1 secretion in vivo

Elevated circulating fasting glucagon-like peptide-1 in surgical patients with aortic valve disease and diabetes

Abstract Background Diabetes is a risk factor for peripheral, coronary, and cerebrovascular disease. In contrast, results also indicate that patients with diabetes have reduced prevalence of aortic aneurysms, although the mechanisms remain largely unknown. We hypothesize that altered endogenous secretion of the intestinal hormone glucagon-like peptide-1 (GLP-1)—previously shown to protect from aneurysm formation, and governing many of the mechanisms thought to be involved in aneurysm formation—may provide insights into the mechanisms underlying the inverse relationship of diabetes and aneurysm. Methods We undertook a case–control study to characterize circulating plasma GLP-1 levels in diabetic and non-diabetic surgical patients with aortic valve disease, and with or without ascending aortic dilation. The cohort included patients with a bicuspid aortic valve (BAV), a common congenital disorder associated with ascending aortic aneurysm, as well as patients with a tricuspid aortic valve (TAV). Results In our patient group, diabetes was characterized by a significant increase in fasting plasma GLP-1 levels. Further, we show that aortic dilation in these patients was associated with a significant increase in fasting plasma GLP-1, although a significant increase in the intact and bioactive peptide could not be detected in BAV patients with aortic dilation. Conclusion A subgroup of diabetic patients with aortic valve pathology have increased fasting plasma GLP-1 levels, which may be of importance for the low prevalence of aortic dilation in this patient group. Further, in TAV patients, GLP-1 secretion and plasma levels of intact GLP-1 are upregulated in association with aortic dilation, possibly indicating a compensatory mechanism

Oleate, but not palmitate, increases the expression of G protein-coupled receptor FFAR1 mRNA and amplifies the acute secretory response of GLP-1 producing cells to fatty acids.

<p>Whereas 0.125 mM palmitate significantly reduced GLUTag proglucagon and FFAR1 (GPR40) / FFAR3 (GPR43) mRNA expression after 48h (A), oleate exposure significantly increased the expression of proglucagon / FFAR 1 (GPR40) and FFAR3 (GPR43) mRNA after 24h / 48h respectively (B). GLP-1 secretion in response to 0.5 mM palmitate was increased 2-fold following a 48h exposure to 0.125mM oleate (C). Comparisons between groups were made by a one-way ANOVA, and Student-Newman-Keul’s <i>post hoc</i> test. Bars represent mean ± SEM. *, <i>p</i><0.05; ***, <i>p</i><0.001 compared with controls. #, <i>p</i><0.05 compared with palmitate-treated cells.</p

Palmitate and oleate exert opposing effects on the formation of reactive oxygen species, activation of the mitogen-activated protein kinase p38 and viability of GLP-1-producing cells.

<p>0.125 mM oleate significantly decreases—while 0.125 mM palmitate significantly increase—caspase-3 activation (<b>A</b>) and DNA fragmentation (<b>B</b>) in GLUTag cells following a 48h incubation. Co-incubation of 0.125mM palmitate with 0.125mM Oleate abolishes palmitate induced caspase-3 activity (<b>C</b>) and DNA fragmentation (D). ROS production in GLP-1-secreting cells after 48 h (<b>E</b>) and phosphorylation of the ROS-sensitive kinase p-38 following 8h (<b>F</b>) is increased in response to 0.125mM palmitate, but not in response to 0.125mM Oleate. Bars represent mean ± SEM for n = 3–6 independent experiments analyzed in duplicates. Comparisons between groups were made by a one-way ANOVA, and Student-Newman-Keul’s <i>post hoc</i> test. *, <i>p</i><0.05; ***, <i>p</i><0.001 compared with control cells. #, <i>p</i><0.05 compared with palmitate-treated cells.</p

MOESM1 of Elevated circulating fasting glucagon-like peptide-1 in surgical patients with aortic valve disease and diabetes

Additional file 1: Table S1. Patient characteristics