Vitamin C further improves the protective effect of GLP-1 on the ischemia-reperfusion-like effect induced by hyperglycemia post-hypoglycemia in type 1 diabetes

Diabetic peripheral neuropathy and glycemic variability assessed by continuous glucose monitoring: A systematic review and meta-analysis

Continuous glucose monitoring (CGM)-derived metrics have been used to accurately assess glycemic variability (GV) to facilitate management of diabetes mellitus, yet their relationship with diabetic peripheral neuropathy (DPN) is not fully understood. We performed a systematic review and meta-analysis to evaluate the association between GV metrics and the risk of developing DPN. Nine studies totaling 3,649 patients with type 1 and type 2 diabetes mellitus were included. A significant association was found between increased GV, as indicated by metrics including standard deviation (SD) with OR and 95% CI of 2.58 (1.45-4.57), mean amplitude of glycemic excursions (MAGE) with OR and 95% CI of 1.90 (1.01-3.58), mean of daily difference (MODD) with OR and 95% CI of 2.88 (2.17-3.81) and the incidence of DPN. Our findings support a link between higher GV and an increased risk of DPN in patients with diabetes. These findings highlight the potential of GV metrics as indicators for the development of DPN, advocating for their inclusion in diabetes management strategies to potentially mitigate neuropathy risk. Longitudinal studies with longer observation periods and larger sample sizes are necessary to validate these associations across diverse populations.

Correlation Between Blood Urea Nitrogen and Short- and Long-Term Glycemic Variability in Elderly Patients with Type 2 Diabetes Mellitus Who Were hospitalized:A Retrospective Study

Objective

Type 2 diabetes mellitus (T2DM) is a metabolic disease characterized by insulin resistance and progressively impaired insulin secretion resulting in dynamic fluctuations in glucose levels.High blood urea nitrogen (BUN) levels have been linked to decreased insulin sensitivity, suppressed insulin synthesis and increased risk of incident diabetes mellitus in humans as well as insulin use in patients with T2DM.This study characterize the association between BUN levels and short-term and long-term glycemic variability(GV) in the elderly patients with T2DM who were hospitalized.

Methods

A total of 927 elderly patients with T2DM were included in the study. The short-term GV was quantified using parameters such as standard deviation (SD), coefficient of variation (CV), time in range (TIR), and mean amplitude of glycemic excursions (MAGE), based on multi-point fingertip blood glucose monitoring. The long-term GV was quantified using parameters such as SD, CV, variation independent of the mean (VIM), and average successive variability (ARV), based on fasting blood glucose(FPG). The relationship between BUN levels and short-term and long-term GV in elderly T2DM who were hospitalized was explored using methods such as Spearman correlation coefficient, linear regression analysis, logistic regression analysis, and interaction tests.

Results

In elderly patients with T2DM were hospitalized, there is a significant correlation between BUN levels and both short-term and long-term GV. BUN is negatively correlated with the GV parameter TIR (r=-0.12, P=0.000), and positively correlated with SD (r=0.12, P=0.000), CV (r=0.07, P=0.026), MAGE (r=0.11, P=0.001), FPG-SD (r=0.08, P=0.013), and FPG-CV (r=0.08, P=0.014).Furthermore, the association remains consistent across different age, gender, BMI, and haemoglobin A1c (HbA1c) subgroups (P interaction > 0.05).

Conclusion

In elderly patients with T2DM were hospitalized, BUN levels were positively associated with GV.Therefore, monitoring BUN levels were beneficial in assessing the degree of GV.

Serum Cytokines and Growth Factors in Subjects with Type 1 Diabetes: Associations with Time in Ranges and Glucose Variability

The detrimental effect of hyperglycemia and glucose variability (GV) on target organs in diabetes can be implemented through a wide network of regulatory peptides. In this study, we assessed a broad panel of serum cytokines and growth factors in subjects with type 1 diabetes (T1D) and estimated associations between concentrations of these molecules with time in ranges (TIRs) and GV. One hundred and thirty subjects with T1D and twenty-seven individuals with normal glucose tolerance (control) were included. Serum levels of 44 cytokines and growth factors were measured using a multiplex bead array assay. TIRs and GV parameters were derived from continuous glucose monitoring. Subjects with T1D compared to control demonstrated an increase in concentrations of IL-1β, IL-1Ra, IL-2Rα, IL-3, IL-6, IL-7, IL-12 p40, IL-16, IL-17A, LIF, M-CSF, IFN-α2, IFN-γ, MCP-1, MCP-3, and TNF-α. Patients with TIR ≤ 70% had higher levels of IL-1α, IL-1β, IL-6, IL-12 p70, IL-16, LIF, M-CSF, MCP-1, MCP-3, RANTES, TNF-α, TNF-β, and b-NGF, and lower levels of IL-1α, IL-4, IL-10, GM-CSF, and MIF than those with TIR > 70%. Serum IL-1β, IL-10, IL-12 p70, MCP-1, MCP-3, RANTES, SCF, and TNF-α correlated with TIR and time above range. IL-1β, IL-8, IL-10, IL-12 p70, MCP-1, RANTES, MIF, and SDF-1α were related to at least one amplitude-dependent GV metric. In logistic regression models, IL-1β, IL-4, IL-10, IL-12 p70, GM-CSF, HGF, MCP-3, and TNF-α were associated with TIR ≤ 70%, and MIF and PDGF-BB demonstrated associations with coefficient of variation values ≥ 36%. These results provide further insight into the pathophysiological effects of hyperglycemia and GV in people with diabetes.

Correlation Between Glycemic Variability and Diabetic Complications: A Narrative Review

Diabetes mellitus is a metabolic disorder with a complex etiology in which glycemic dynamics are disturbed and the body is unable to maintain the process of glucose homeostasis through the pancreas. Persistent symptoms of high blood glucose or low blood glucose may lead to diabetic complications, such as neuropathy, nephropathy, retinopathy, and cardiovascular diseases. Glycemic variability which can represent the presence of excessive glycemic excursions is an indicator for evaluating glucose homoeostasis. Limiting glycemic variability has gradually become an emerging therapeutic target in improve diabetes metabolism and prevent associated complications. This article reviews the progress of research on the various quantifiable parameters of glycemic variability and their relationships with vascular lesions and mechanisms.

Oral glucagon-like peptide 1 analogue ameliorates glucose intolerance in db/db mice

OBJECTIVES

We constructed a recombinant oral GLP-1 analogue in Lactococcus lactis (L. lactis) and evaluated its physiological functions.

RESULTS

In silico docking suggested the alanine at position 8 substituted with serine (A8SGLP-1) reduced binding of DPP4, which translated to reduced cleavage by DPP4 with minimal changes in stability. This was further confirmed by an in vitro enzymatic assay which showed that A8SGLP-1 significantly increased half-life upon DPP4 treatment. In addition, recombinant L. lactis (LL-A8SGLP-1) demonstrated reduced fat mass with no changes in body weight, significant improvement of random glycemic control and reduced systemic inflammation compared with WT GLP-1 in db/db mice.

CONCLUSION

LL-A8SGLP-1 adopted in live biotherapeutic products reduce blood glucose in db/db mice without affecting its function.

Glucose Variability: How Does It Work?

A growing body of evidence points to the role of glucose variability (GV) in the development of the microvascular and macrovascular complications of diabetes. In this review, we summarize data on GV-induced biochemical, cellular and molecular events involved in the pathogenesis of diabetic complications. Current data indicate that the deteriorating effect of GV on target organs can be realized through oxidative stress, glycation, chronic low-grade inflammation, endothelial dysfunction, platelet activation, impaired angiogenesis and renal fibrosis. The effects of GV on oxidative stress, inflammation, endothelial dysfunction and hypercoagulability could be aggravated by hypoglycemia, associated with high GV. Oscillating hyperglycemia contributes to beta cell dysfunction, which leads to a further increase in GV and completes the vicious circle. In cells, the GV-induced cytotoxic effect includes mitochondrial dysfunction, endoplasmic reticulum stress and disturbances in autophagic flux, which are accompanied by reduced viability, activation of apoptosis and abnormalities in cell proliferation. These effects are realized through the up- and down-regulation of a large number of genes and the activity of signaling pathways such as PI3K/Akt, NF-κB, MAPK (ERK), JNK and TGF-β/Smad. Epigenetic modifications mediate the postponed effects of glucose fluctuations. The multiple deteriorative effects of GV provide further support for considering it as a therapeutic target in diabetes.

Vitamin C supplementation reduces expression of circulating miR-451a in subjects with poorly controlled type 2 diabetes mellitus and high oxidative stress

Background

Vitamin C is an essential element required for normal metabolic function. We investigated the effect of vitamin C supplementation on circulating miRNA (miR) expression in subjects with poorly controlled type 2 diabetes mellitus (T2DM). Changes in miR expression were also correlated with clinical measures of disease.

Methods

Pre- and post-vitamin C supplementation samples from five participants who had increased vitamin C levels, improved oxidative status and polymorphonuclear (PMN) function after receiving 1,000 mg of vitamin C daily for six weeks were screened for miRNA expression using the NanoString miRNA assay. Differences in miRNA expression identified from the miRNA screen were validated by qRT-PCR.

Results

Four miRNAs showed significantly different expression post-vitamin C supplementation relative to baseline, including the down-regulation of miR-451a (−1.72 fold change (FC), p = 0.036) and up-regulation of miR-1253 (0.62 FC, p = 0.027), miR-1290 (0.53 FC, p = 0.036) and miR-644a (0.5 FC, p = 0.042). The validation study showed only miR-451a expression was significantly different from baseline with vitamin C supplementation. MiR-451a expression was negatively correlated with vitamin C levels (r =  − 0.497, p = 0.049) but positively correlated with levels of malondialdehyde (MDA) (r = 0.584, p = 0.017), cholesterol (r = 0.564, p = 0.022) and low-density lipoproteins (LDL) (r = 0.522, p = 0.037). Bioinformatics analysis of the putative target genes of miR-451a indicated gene functions related to signaling pathways involved in cellular processes, such as the mammalian target of rapamycin (mTOR) signaling pathway.

Conclusions

Vitamin C supplementation altered circulating miR-451a expression. The results from this pilot study suggest that miRNAs could be used as biomarkers to indicate oxidative status in subjects with T2DM and with poor glycemic control and could lead to a novel molecular strategy to reduce oxidative stress in T2DM.

Interleukin-6 response to insulin-induced hypoglycemia is associated with hypothalamic-pituitary-adrenal axis activation

Increased plasma levels of interleukin-6 (IL-6) in response to acute hypoglycemia have been well documented. Aiming to study the interaction between IL-6 and counter-regulatory hormones during hypoglycemic stress we conducted an exploratory single center study involving 26 adult patients undergoing insulin tolerance test. Insulin-induced hypoglycemia elicited a significant dynamic response of IL-6, adrenaline, noradrenaline, GH, prolactin, ACTH and serum and salivary cortisol (P < 0.001 for all variables). Patients with insufficient HPA axis response had lower hypoglycemia-induced IL-6 increase (median: 0.88 pg/mL) compared with individuals with intact HPA axis response (2.03 pg/mL, P = 0.007). IL-6 maximal increase correlated with the maximal increase of serum cortisol (rs = 0.48; P = 0.013), salivary cortisol (rs = 0.66; P = 0.012), plasma ACTH (rs = 0.48; P = 0.013) and with the increase in procedure-related symptoms of anxiety and hypoglycemia (rs = 0.57; P = 0.003). In conclusion, hypoglycemic stress-induced IL-6 increase is associated with activation of the HPA axis, suggesting that IL-6 response to hypoglycemic stress may be regarded as part of the counter-regulatory response, possibly contributing to the maintenance of glucose homeostasis.

The effect of insulin-induced hypoglycemia on inflammatory markers: A systematic review

INTRODUCTION

The effects of acute hypoglycemia on markers of inflammation have been investigated, but the results have been heterogeneous.

OBJECTIVE

We aimed to perform a systematic review about the acute effects of insulin-induced hypoglycemia on inflammatory markers in patients with diabetes as well as non-diabetic subjects.

METHODS

A systematic search of the literature using the electronic databases MEDLINE and SCOPUS was conducted through September 2017. Search terms included: "hypoglycemia"," insulin", "cytokines", and "inflammation". We included original studies assessing peripheral inflammatory markers during insulin-induced hypoglycemia in humans.

RESULTS

Two hundred twenty-two citations were initially retrieved. Eleven studies were included in our systematic review. Acute hypoglycemia increases total leukocyte number and several pro-inflammatory markers. Elevation in pro-inflammatory markers in response to insulin-induced acute hypoglycemia appears to be of similar magnitude in non-diabetic subjects and in type-1 diabetic patients with intact awareness of hypoglycemia. Adrenaline rises in response to acute hypoglycemia correlates with the increase of pro-inflammatory markers.

CONCLUSION

Acute hypoglycemia induces a pro-inflammatory state in both type-1 diabetic and non-diabetic subjects with no apparent significant difference between these two populations. Activation of the sympathetic nervous system is a likely mediator of these effects.

Does Glucagon-like Peptide-1 Ameliorate Oxidative Stress in Diabetes? Evidence Based on Experimental and Clinical Studies

Glucagon-like peptide-1 (GLP-1) has shown to influence the oxidative stress status in a number of in vitro, in vivo and clinical studies. Well-known effects of GLP-1 including better glycemic control, decreased food intake, increased insulin release and increased insulin sensitivity may indirectly contribute to this phenomenon, but glucose-independent effects on ROS level, production and antioxidant capacity have been suggested to also play a role. The potential 'antioxidant' activity of GLP-1 along with other proposed glucose-independent modes of action related to ameliorating redox imbalance remains a controversial topic but could hold a therapeutic potential against micro- and macrovascular diabetic complications. This review discusses the presently available knowledge from experimental and clinical studies on the effects of GLP-1 on oxidative stress in diabetes and diabetes-related complications.

Association of low GLP-1 with oxidative stress is related to cardiac disease and outcome in patients with type 2 diabetes mellitus: a pilot study

Oxidative stress (OS) contributes to cardiovascular damage in type 2 diabetes mellitus (T2DM). The peptide glucagon-like peptide-1 (GLP-1) inhibits OS and exerts cardiovascular protective actions. Our aim was to investigate whether cardiac remodeling (CR) and cardiovascular events (CVE) are associated with circulating GLP-1 and biomarkers of OS in T2DM patients. We also studied GLP-1 antioxidant effects in a model of cardiomyocyte lipotoxicity. We examined 72 T2DM patients with no coronary or valve heart disease and 14 nondiabetic subjects. A median of 6 years follow-up information was obtained in 60 patients. Circulating GLP-1, dipeptidyl peptidase-4 activity, and biomarkers of OS were quantified. In T2DM patients, circulating GLP-1 decreased and OS biomarkers increased, compared with nondiabetics. Plasma GLP-1 was inversely correlated with serum 3-nitrotyrosine in T2DM patients. Patients showing high circulating 3-nitrotyrosine and low GLP-1 levels exhibited CR and higher risk for CVE, compared to the remaining patients. In palmitate-stimulated HL-1 cardiomyocytes, GLP-1 reduced cytosolic and mitochondrial oxidative stress, increased mitochondrial ATP synthase expression, partially restored mitochondrial membrane permeability and cytochrome c oxidase activity, blunted leakage of creatine to the extracellular medium, and inhibited oxidative damage in total and mitochondrial DNA. These results suggest that T2DM patients with reduced circulating GLP-1 and exacerbated OS may exhibit CR and be at higher risk for CVE. In addition, GLP-1 exerts antioxidant effects in HL-1 palmitate-overloaded cardiomyocytes. It is proposed that therapies aimed to increase GLP-1 may counteract OS, protect from CR, and prevent CVE in patients with T2DM.

Effects of exenatide on postprandial vascular endothelial dysfunction in type 2 diabetes mellitus

Background

Basic studies have shown that glucagon-like peptide-1 (GLP-1) analogs exert a direct protective effect on the vascular endothelium in addition to their indirect effects on postprandial glucose and lipid metabolism. GLP-1 analogs are also reported to inhibit postprandial vascular endothelial dysfunction. This study examined whether the GLP-1 analog exenatide inhibits postprandial vascular endothelial dysfunction in patients with type 2 diabetes mellitus (T2DM).

Methods

Seventeen patients with T2DM underwent a meal tolerance test to examine changes in postprandial vascular endothelial function and in glucose and lipid metabolism, both without exenatide (baseline) and after a single subcutaneous injection of 10 μg exenatide. Vascular endothelial function was determined using reactive hyperemia index (RHI) measured by peripheral arterial tonometry before and 120 min after the meal loading test. The primary endpoint was the difference in changes in postprandial vascular endothelial function between the baseline and exenatide tests.

Results

The natural logarithmically-scaled RHI (L_RHI) was significantly lower after the baseline meal test but not in the exenatide test. The use of exenatide resulted in a significant decrease in triglycerides (TG) area under the curve and coefficient of variation (CV). The change in L_RHI correlated with changes in CV of triglycerides and HDL-cholesterol. Multivariate analysis identified changes in triglyceride CV as the only determinant of changes in L_RHI, contributing to 41% of the observed change.

Conclusions

Exenatide inhibited postprandial vascular endothelial dysfunction after the meal loading test, suggesting that exenatide has a multiphasic anti-atherogenic action involving not only glucose but also lipid metabolism.

Trial registration

ClinicalTrials.gov: UMIN000015699.

The protective effect of the Mediterranean diet on endothelial resistance to GLP-1 in type 2 diabetes: a preliminary report

BACKGROUND

In type 2 diabetes, acute hyperglycemia worsens endothelial function and inflammation,while resistance to GLP-1 action occurs. All these phenomena seem to be related to the generation of oxidative stress. A Mediterranean diet, supplemented with olive oil, increases plasma antioxidant capacity, suggesting that its implementation can have a favorable effect on the aforementioned phenomena. In the present study, we test the hypothesis that a Mediterranean diet using olive oil can counteract the effects of acute hyperglycemia and can improve the resistance of the endothelium to GLP-1 action.

METHODS

Two groups of type 2 diabetic patients, each consisting of twelve subjects, participated in a randomized trial for three months, following a Mediterranean diet using olive oil or a control low-fat diet. Plasma antioxidant capacity, endothelial function, nitrotyrosine, 8-iso-PGF2a, IL-6 and ICAM-1 levels were evaluated at baseline and at the end of the study. The effect of GLP-1 during a hyperglycemic clamp, was also studied at baseline and at the end of the study.

RESULTS

Compared to the control diet, the Mediterranean diet increased plasma antioxidant capacity and improved basal endothelial function, nitrotyrosine, 8-iso-PGF2a, IL-6 and ICAM-1 levels. The Mediterranean diet also reduced the negative effects of acute hyperglycemia, induced by a hyperglycemic clamp, on endothelial function, nitrotyrosine, 8-iso-PGF2a, IL-6 and ICAM-1 levels. Furthermore, the Mediterranean diet improved the protective action of GLP-1 on endothelial function, nitrotyrosine, 8-iso-PGF2a, IL-6 and ICAM-1 levels, also increasing GLP-1-induced insulin secretion.

CONCLUSIONS

These data suggest that the Mediterranean diet, using olive oil, prevents the acute hyperglycemia effect on endothelial function, inflammation and oxidative stress, and improves the action of GLP-1, which may have a favorable effect on the management of type 2 diabetes, particularly for the prevention of cardiovascular disease.

Effect of vitamin C on endothelial function in health and disease: a systematic review and meta-analysis of randomised controlled trials

BACKGROUND

Observational studies indicate that higher vitamin C intake is associated with reduced risk for cardiovascular diseases. However, randomised controlled trials (RCT) examining the effect of vitamin C on endothelial function (EF) have reported inconsistent results. The aims of this systematic review and meta-analysis were to determine the effect of vitamin C supplementation on EF and to investigate whether the effect was influenced by health status, study duration, dose and route of vitamin C administration.

METHODS

We searched the Medline, Embase, Cochrane Library, and Scopus databases from inception to May 2013 for studies that met the following criteria: 1) RCT with adult participants, 2) vitamin C administered alone, 3) studies that quantified EF using commonly applied methods including ultrasound, plethysmography and pulse wave analysis.

RESULTS

Pooling the data from 44 clinical trials showed a significant positive effect of vitamin C on EF (SMD: 0.50, 95% CI: 0.34, 0.66, P < 0.001). Stratification of the analysis by health outcome revealed improved EF in atherosclerotic (SMD: 0.84, 95% CI: 0.41, 1.26, P < 0.001), diabetic (SMD: 0.52, 95% CI: 0.21, 0.82, P < 0.001) and heart failure patients (SMD: 0.48, 95% CI: 0.08, 0.88, P < 0.02) after vitamin C supplementation. The effect size appeared to be unaffected by study design, duration, baseline plasma vitamin C concentration or route of administration of vitamin C. The meta-regression showed a significant positive association between vitamin C dose and improvement in EF (β: 0.00011, 95% CI: 0.00001, 0.00021, P = 0.03).

CONCLUSIONS

Vitamin C supplementation improved EF. The effect of vitamin C supplementation appeared to be dependent on health status, with stronger effects in those at higher cardiovascular disease risk. PROSPERO Database registration: CRD42013004567, http://www.crd.york.ac.uk/prospero/

Methylglyoxal modulates endothelial nitric oxide synthase-associated functions in EA.hy926 endothelial cells

BACKGROUND

Increased levels of the sugar metabolite methylglyoxal (MG) in vivo were shown to participate in the pathophysiology of vascular complications in diabetes. Alterations of endothelial nitric oxide synthase (eNOS) activity by hypophosphorylation of the enzyme and enhanced monomerization are found in the diabetic milieu, and the regulation of this still remains undefined. Using various pharmacological approaches, we elucidate putative mechanisms by which MG modulates eNOS-associated functions of MG-stimulated superoxide O₂•⁻ production, phosphorylation status and eNOS uncoupling in EA.hy926 human endothelial cells.

METHODS

In cultured EA.hy926 endothelial cells, the effects of MG treatment, tetrahydrobiopterin (BH4; 100 μM) and sepiapterin (20 μM) supplementation, NOS inhibition by N(G)-nitro-L-arginine methyl ester (L-NAME; 50 μM), and inhibition of peroxynitrite (ONOO⁻) formation (300 μM Tempol plus 50 μM L-NAME) on eNOS dimer/monomer ratios, Ser-1177 eNOS phosphorylation and 3-nitrotyrosine (3NT) abundance were quantified using immunoblotting. O₂•⁻-dependent fluorescence was determined using a commercially available kit and tissue biopterin levels were measured by fluorometric HPLC analysis.

RESULTS

In EA.hy926 cells, MG treatment significantly enhanced O₂•⁻ generation and 3NT expression and reduced Ser-1177 eNOS phosphorylation, eNOS dimer/monomer ratio and cellular biopterin levels indicative of eNOS uncoupling. These effects were significantly mitigated by administration of BH4, sepiapterin and suppression of ONOO⁻ formation. L-NAME treatment significantly blunted eNOS-derived O₂•⁻ generation but did not modify eNOS phosphorylation or monomerization.

CONCLUSION

MG triggers eNOS uncoupling and hypophosphorylation in EA.hy926 endothelial cells associated with O₂•⁻ generation and biopterin depletion. The observed effects of the glycolysis metabolite MG presumably account, at least in part, for endothelial dysfunction in diabetes.