Impact of dietary supplementation of glycocalyx precursors on vascular function in type 2 diabetes

Abstract

Degradation of the endothelial glycocalyx in type 2 diabetes (T2D) is thought to contribute to impaired shear stress mechanotransduction, leading to endothelial dysfunction and the development of cardiovascular disease. Herein, we tested the hypothesis that restoration of the endothelial glycocalyx with dietary supplementation of glycocalyx precursors (DSGPs, containing glucosamine sulfate, fucoidan, superoxide dismutase, and high-molecular weight hyaluronan) improves endothelial function and other indices of vascular function in T2D. First, in db/db mice, we showed that treatment with DSGP (100 mg/kg/day) for 4 wk restored endothelial glycocalyx length, as assessed via atomic force microscopy in aortic explants. Restoration of the glycocalyx with DSGP was accompanied by improved flow-mediated dilation (FMD) and reduced arterial stiffness in isolated mesenteric arteries. Further corroborating these findings, the treatment of cultured endothelial cells with that same mixture of glycocalyx precursors promoted glycocalyx growth. Next, as an initial step to investigate the translatability of these findings, we conducted a pilot (n = 22) double-blinded randomized placebo-controlled clinical trial to assess the effects of DSGP (3,712.5 mg/day) for 8 wk on endothelial glycocalyx integrity and indices of vascular function, including FMD, in Veterans with T2D. Contrary to the hypothesis, DSGP neither enhanced endothelial glycocalyx integrity nor improved vascular function indices relative to placebo. Together, these findings conceptually support the notion that restoration of the endothelial glycocalyx can lead to improvements in vascular function in a mouse model of T2D; however, DSGP as a therapeutic strategy to enhance vascular function in individuals with T2D does not appear to be efficacious.NEW & NOTEWORTHY Endothelial glycocalyx degradation in type 2 diabetes (T2D) is thought to contribute to impaired shear stress mechanotransduction, leading to vascular dysfunction. The findings of this study support the notion that restoration of the endothelial glycocalyx using a dietary supplementation of glycocalyx precursors can lead to improvements in vascular function in diabetic mice. However, the utilized dietary supplement as a therapeutic strategy to enhance vascular function in individuals with T2D is not efficacious.

Keywords: diabetes; dietary supplement; endothelial function; glycocalyx.

Graphical abstract

Figure 1.

Experimental design of the clinical trial. Following randomization to either dietary supplementation of glycocalyx precursors (DSGPs) treatment or placebo, and at least 24 h prior, but within 7 days of their baseline and final study visits, participants were fitted with a 24-h ambulatory blood pressure monitor for blood pressure assessments.

Figure 2.

Vascular effects of treatment with dietary supplementation of glycocalyx precursors (DSGPs) vs. vehicle (Veh) in db/db mice, and the effect of glycocalyx precursors on glycocalyx coverage in cultured endothelial cells. A: endothelial glycocalyx length, as well as glycocalyx and cell cortical stiffness, was assessed in en face aortic explants (schematic representation shown in the inset) using atomic force microscopy in db/+ control mice and in db/db mice treated with DSGP vs. vehicle for 4 wk. Statistical analysis was performed using one-way ANOVA with Bonferroni post hoc test; n = 9–20/group. B: flow-mediated dilation (FMD) and sodium nitroprusside (SNP)-induced dilation in isolated mesenteric arteries. Data are expressed as percentages of dilation from phenylephrine preconstriction in response to increasing flow rates or SNP concentrations. Mesenteric artery stiffness was assessed via the incremental modulus of elasticity (E_inc) at increasing intraluminal pressures under calcium-free conditions. Statistical analysis was performed using two-way ANOVA with repeated measures and Bonferroni post hoc test; n = 8–9/group. C: aortic relaxation was assessed in response to increasing concentrations of acetylcholine (ACh) and SNP following preconstriction with U46619. Statistical analysis was performed using two-way ANOVA with repeated measures and Bonferroni post hoc test; n = 6–16/group. D: human umbilical vein endothelial cells exposed to neuraminidase to induce glycocalyx degradation were treated with vehicle vs. the cocktail of glycocalyx precursors (GP) for 48 h. Glycocalyx coverage was determined by staining with fluorescent wheat germ agglutinin (WGA) and fluorescence intensity quantification. Statistical analysis was performed using unpaired Student’s t tests; n = 11–12/condition. Data are presented as means ± SE. Individual data points are also presented as appropriate. *P < 0.05 vs. db/+, #P < 0.05 vs. db/db + Veh or Veh.

Figure 3.

Flow diagram for the clinical trial. DSGP, dietary supplementation of glycocalyx precursors.

Figure 4.

Vascular effects of dietary supplementation of glycocalyx precursors (DSGPs) treatment vs. placebo in Veterans with type 2 diabetes. A: delta change in perfused boundary region (PBR) from pre- to postintervention. Statistical analysis was performed using unpaired Student’s t tests; n = 10–12/group. B: delta change in brachial and femoral artery flow-mediated dilation (FMD) from pre- to postintervention. Statistical analysis was performed using unpaired Student’s t tests; n = 10–12/group. C: delta change in plasma nitrite from pre- to postintervention. Statistical analysis was performed using unpaired Student’s t tests; n = 10–12/group. D: delta change in carotid-to-femoral pulse wave velocity (cfPWV) from pre- to postintervention. Statistical analysis was performed using unpaired Student’s t tests; n = 8–11/group. E: delta change in 24-h average mean arterial blood pressure (MAP) from pre- to postintervention. Statistical analysis was performed using unpaired Student’s t tests; n = 9–11/group. F: delta change in leg blood flow and vascular conductance, skeletal muscle (SkM) perfusion, and total peripheral resistance (TPR) response to insulin from pre- to postintervention. Measurements were performed at baseline and at 60 min of systemic insulin infusion (with the coinfusion of dextrose to maintain euglycemia). The difference between time points was then calculated to capture the insulin response as the outcome variable. Statistical analysis of normally distributed data (SkM perfusion) was performed using unpaired Student’s t tests. Non normally distributed data (leg blood flow, vascular conductance, and TPR) were analyzed using unpaired Mann–Whitney U (Wilcoxon rank-sum) test; n = 9–12/group. Data are presented as means ± SE. Individual data points are also presented. P values for all comparisons are shown.