Flavonoids and Insulin-Resistance: From Molecular Evidences to Clinical Trials

Insulin-resistance is one of the main factors responsible for the onset and progression of Metabolic Syndrome (MetS). Among all polyphenols, the effects of flavonoids and their main food sources on insulin sensitivity have been widely evaluated in molecular and clinical studies. The aim of this review is to analyse the data observed in vitro, in vivo and in clinical trials concerning the effects of flavonoids on insulin resistance and to determine the molecular mechanisms with which flavonoids interact with insulin signaling

Retinal neurodegeneration in patients with type 1 diabetes mellitus: the role of glycemic variability

Aims: Recent studies have identified neuroretinal abnormalities in persons affected by diabetes mellitus, before the onset of microvascular alterations. However, the role of glycemic variability (GV) on early retinal neurodegeneration is still not clarified. Methods: To explore the relationship between glycemic control and neuroretinal characteristics, 37 persons with Type 1 diabetes mellitus (Type 1 DM) divided into two groups with no signs (noRD) and with mild non-proliferative diabetic retinopathy (NPDR) compared to 13 healthy control participants (C) were recruited. All persons underwent an optical coherence tomography with automatic segmentation of all neuroretinal layers. Measurements of mean of nasal (N)/temporal (T)/superior (S)/inferior (I) macular quadrants for individual layer were also calculated. Metabolic control was evaluated by glycated hemoglobin (HbA1c), and indexes of GV were calculated from continuous glucose monitoring. Results: The difference among the three groups in terms of RNFL thickness was significantly dependent on quadrant (F(6;132) = 2.315; p = 0.037). This interaction was due to a specific difference in RNFL-N thickness, where both Type 1 DM groups showed a similar reduction versus C (−3.9 for noDR and −4.9 for NPDR), without any relevant difference between them (−1.0). Inner nuclear layer (INL) was increased in all quadrants in the two Type 1 DM groups compared to C (mean difference = 7.73; 95% CI: 0.32–15.14, p = 0.043; mean difference = 7.74; 95% CI: 0.33–15.15, p = 0.043, respectively). A negative correlation between RNFL-N and low blood glucose index (r = −0.382, p = 0.034) and positive correlation between INL and continuous overall net glycemic action −1, −2, −4 h (r = 0.40, p = 0.025; r = 0.39, p = 0.031; r = 0.41, p = 0.021, respectively) were observed in Type 1 DM patients. The triglycerides were positively and significantly correlated to INL (r = 0.48, p = 0.011), in Type 1 DM subjects. GV and triglycerides resulted both independent predictors of increased INL thickness. No correlation was found with HbA1c. Conclusions: Early structural damage of neuroretina in persons with Type 1 DM patients is related to glucose fluctuations. GV should be addressed, even in the presence of a good metabolic control

FMD, shear rate FMD and VMR in diabetic and control groups.

<p>Legend: FMD (Flow-Mediated Dilation, %); shear rate FMD (%); VMR (Cerebral Vasomotor Reactivity, %), LF/HF ratio (Low Frequency/High Frequency ratio). Data are expressed as mean ± SD.</p

Autoantibody and T cell responses to oxidative post-translationally modified insulin neoantigenic peptides in type 1 diabetes

Aims/hypothesis: Antibodies specific to oxidative post-translational modifications (oxPTM) of insulin (oxPTM-INS) are present in most individuals with type 1 diabetes, even before the clinical onset. However, the antigenic determinants of such response are still unknown. In this study, we investigated the antibody response to oxPTM-INS neoepitope peptides (oxPTM-INSPs) and evaluated their ability to stimulate humoral and T cell responses in type 1 diabetes. We also assessed the concordance between antibody and T cell responses to the oxPTM-INS neoantigenic peptides. Methods: oxPTM-INS was generated by exposing insulin to various reactive oxidants. The insulin fragments resulting from oxPTM were fractionated by size-exclusion chromatography further to ELISA and LC-MS/MS analysis to identify the oxidised peptide neoepitopes. Immunogenic peptide candidates were produced and then modified in house or designed to incorporate in silico-oxidised amino acids during synthesis. Autoantibodies to the oxPTM-INSPs were tested by ELISA using sera from 63 participants with new-onset type 1 diabetes and 30 control participants. An additional 18 fresh blood samples from participants with recently diagnosed type 1 diabetes, five with established disease, and from 11 control participants were used to evaluate, in parallel, CD4+ and CD8+ T cell activation by oxPTM-INSPs. Results: We observed antibody and T cell responses to three out of six LC-MS/MS-identified insulin peptide candidates: A:12–21 (SLYQLENYCN, native insulin peptide 3 [Nt-INSP-3]), B:11–30 (LVEALYLVCGERGFFYTPKT, Nt-INSP-4) and B:21–30 (ERGFFYTPKT, Nt-INSP-6). For Nt-INSP-4 and Nt-INSP-6, serum antibody binding was stronger in type 1 diabetes compared with healthy control participants (p≤0.02), with oxidised forms of ERGFFYTPKT, oxPTM-INSP-6 conferring the highest antibody binding (83% binders to peptide modified in house by hydroxyl radical [●OH] and &gt;88% to in silico-oxidised peptide; p≤0.001 vs control participants). Nt-INSP-4 induced the strongest T cell stimulation in type 1 diabetes compared with control participants for both CD4+ (p&lt;0.001) and CD8+ (p=0.049). CD4+ response to oxPTM-INSP-6 was also commoner in type 1 diabetes than in control participants (66.7% vs 27.3%; p=0.039). Among individuals with type 1 diabetes, the CD4+ response to oxPTM-INSP-6 was more frequent than to Nt-INSP-6 (66.7% vs 27.8%; p=0.045). Overall, 44.4% of patients showed a concordant autoimmune response to oxPTM-INSP involving simultaneously CD4+ and CD8+ T cells and autoantibodies. Conclusions/interpretation: Our findings support the concept that oxidative stress, and neoantigenic epitopes of insulin, may be involved in the immunopathogenesis of type 1 diabetes. Graphical abstract: [Figure not available: see fulltext.].</p

Autoantibody and T cell responses to oxidative post-translationally modified insulin neoantigenic peptides in type 1 diabetes

Aims/hypothesis Antibodies specific to oxidative post-translational modifications (oxPTM) of insulin (oxPTM-INS) are present in most individuals with type 1 diabetes, even before the clinical onset. However, the antigenic determinants of such response are still unknown. In this study, we investigated the antibody response to oxPTM-INS neoepitope peptides (oxPTM-INSPs) and evaluated their ability to stimulate humoral and T cell responses in type 1 diabetes. We also assessed the concordance between antibody and T cell responses to the oxPTM-INS neoantigenic peptides. Methods oxPTM-INS was generated by exposing insulin to various reactive oxidants. The insulin fragments resulting from oxPTM were fractionated by size-exclusion chromatography further to ELISA and LC-MS/MS analysis to identify the oxidised peptide neoepitopes. Immunogenic peptide candidates were produced and then modified in house or designed to incorporate in silico-oxidised amino acids during synthesis. Autoantibodies to the oxPTM-INSPs were tested by ELISA using sera from 63 participants with new-onset type 1 diabetes and 30 control participants. An additional 18 fresh blood samples from participants with recently diagnosed type 1 diabetes, five with established disease, and from 11 control participants were used to evaluate, in parallel, CD4(+) and CD8(+) T cell activation by oxPTM-INSPs. Results We observed antibody and T cell responses to three out of six LC-MS/MS-identified insulin peptide candidates: A:12-21 (SLYQLENYCN, native insulin peptide 3 [Nt-INSP-3]), B:11-30 (LVEALYLVCGERGFFYTPKT, Nt-INSP-4) and B:21-30 (ERGFFYTPKT, Nt-INSP-6). For Nt-INSP-4 and Nt-INSP-6, serum antibody binding was stronger in type 1 diabetes compared with healthy control participants (p &amp;lt;= 0.02), with oxidised forms of ERGFFYTPKT, oxPTM-INSP-6 conferring the highest antibody binding (83% binders to peptide modified in house by hydroxyl radical [(OH)-O-?] and &amp;gt;88% to in silico-oxidised peptide; p &amp;lt;= 0.001 vs control participants). Nt-INSP-4 induced the strongest T cell stimulation in type 1 diabetes compared with control participants for both CD4(+) (p&amp;lt;0.001) and CD8(+) (p=0.049). CD4(+) response to oxPTM-INSP-6 was also commoner in type 1 diabetes than in control participants (66.7% vs 27.3%; p=0.039). Among individuals with type 1 diabetes, the CD4(+) response to oxPTM-INSP-6 was more frequent than to Nt-INSP-6 (66.7% vs 27.8%; p=0.045). Overall, 44.4% of patients showed a concordant autoimmune response to oxPTM-INSP involving simultaneously CD4(+) and CD8(+) T cells and autoantibodies. Conclusions/interpretation Our findings support the concept that oxidative stress, and neoantigenic epitopes of insulin, may be involved in the immunopathogenesis of type 1 diabetes.Funding Agencies|JDRF [1-SRA-2017-512-Q-R]; European Foundation for the Study of Diabetes Future Leaders Mentorship Programme for Clinical Diabetologists 2018; Italian Ministry of Health [GR-201812365982]; AstraZeneca; Ordine dei Medici ed Odontoiatri di Salerno (OMCeO Salerno); European Foundation for the Study of Diabetes/Novo Nordisk Programme for Diabetes Research in Europe 2020; Fondazione Italiana Sclerosi Multipla [2020/R/13]; Progetti di Rilevante Interesse Nazionale [202077EYN7]</p

Very-low-calorie diet: a quick therapeutic tool to improve β cell function in morbidly obese patients with type 2 diabetes

Background: Caloric restriction in obese diabetic patients quickly improves glucose control, independently from weight loss. However, the early effects of a very-low-calorie diet (VLCD) on insulin sensitivity and insulin secretion in morbidly obese patients with type 2 diabetes are still unclear. Objective: The objective was to study the relative contributions of insulin sensitivity, insulin secretion, or both to improvement in glucose metabolism, after 1 wk of caloric restriction, in severely obese diabetic patients. Design: Hyperglycemic clamps were performed in 14 severely obese (BMI, in kg/m2: .40) patients with type 2 diabetes in good glucose control (glycated hemoglobin , 7.5%) before and after 7 d of a VLCD (400 kcal/d). Results: The VLCD caused a 3.22 6 0.56% weight loss (P , 0.001), 42.0% of which was fat loss, accompanied by decreases in fasting plasma glucose (P , 0.05) and triglycerides (P ,0.01). In parallel, the Disposition Index, which measures the body’s capability to dispose of glucose load, increased from 59.0 6 6.3 to 75.5 6 6.3 mL min21 m22 body surface area (P , 0.01), because of improvements in indexes of both first- and second-phase insulin secretion (P , 0.02), but with no changes in insulin sensitivity (P =0.33). Conclusion: The marked improvement in metabolic profile, observed in severely obese patients with type 2 diabetes after a 7-d VLCD, was primarily due to the amelioration of b cell function, whereas no contribution of insulin sensitivity was shown