HDL cholesterol is an independent predictor of β-cell function decline and incident type 2 diabetes: A longitudinal study

Are Oxidative Stress Biomarkers Reliable Part of Multimarker Panel in Female Patients with Type 2 Diabetes Mellitus?

Background: Oxidative stress and inflammation are the key features of metabolic diseases, including type 2 diabetes mellitus (T2D). However, studies that explored redox homeostasis parameters in relation to T2D show discrepant results. Accordingly, we aimed to examine the potential reliability of oxidative stress biomarkers [i.e., determined by malondialdehyde (MDA), advanced oxidation protein products (AOPP) and catalase (CAT)] in addition to traditional cardiometabolic parameters in relation to T2D in female cohort. Methods: A total of 214 women (of them 40.6% T2D) were consecutively recruited in the study. Principal component analysis with varimax rotation was performed to determine the adequate number of factors consisting of anthropometric, traditional cardiometabolic and redox status markers. Results: MDA and AOPP concentrations were lower, but CAT activity was higher in T2D group as compared with controls (P < 0.001, P = 0.002, P < 0.001). Traditional markers related factor (i.e., with positive loading of waist circumference, triglycerides, uric acid, high sensitivity C-reactive protein and negative loadings of high-density lipoprotein cholesterol) was found to be independently related with T2D in multivariate binary regression analysis, whereas oxidative stress related factor (i.e., with positive loading of MDA and AOPP) lost its independent prediction after adjustment for confounding factors (i.e., age, menopausal status, antihypertensive, and hypolipemic therapies). Increased Traditional markers related factor was associated with more than three times higher probability for T2D onset (OR = 3.319, p < 0.001). Conclusion: Oxidative stress biomarkers, i.e., MDA, AOPP, and CAT are not superior over traditional cardiometabolic markers in relation to T2D in female population. Future studies with both gender included are needed to confirm such results.

Interaction between the GCKR rs1260326 variant and serum HDL cholesterol contributes to HOMA-β and ISIMatusda in the middle-aged T2D individuals

This study aims to investigate the correlations between islet function/ insulin resistance and serum lipid levels, as well as to assess whether the strength of such correlations is affected by the GCKR rs1260326 variant in healthy and T2D individuals. We performed an oral glucose tolerance test (OGTT) on 4889 middle-aged adults, including 3135 healthy and 1754 T2D individuals from the REACTION population study in the Nanjing region. We also measured their serum lipid levels and genotyped for rs1260326. We found that serum high-density lipoprotein (HDL) cholesterol and triglyceride (TG) levels were independently correlated with indexes of islet function (HOMA-β and IGI [insulinogenic index]) and insulin resistance (HOMO-IR and ISIMatsuda) in both healthy and T2D individuals. The correlations were significantly decreased in T2D individuals, with significant heterogeneities compared to healthy controls (I2 > 75%, Phet < 0.05). Although no correlation was observed between serum total cholesterol (TC) level and islet function/ insulin resistance in healthy controls, significant correlations were found in T2D individuals, with significant heterogeneity to healthy controls in the correlation with ISIMatsuda(I2 = 85.3%, Phet = 0.009). Furthermore, we found significant interactions of the GCKR rs1260326 variant for the correlations between serum HDL cholesterol and HOMA-β/ISIMatsuda in T2D subjects (P = 0.015 and 0.038, respectively). These findings illustrate that distinct correlations between serum lipid levels and islet function/ insulin resistance occurred in T2D subjects compared to healthy individuals. Common gene variants, such as rs1260326, might interact substantially when studied in specific populations, especially T2D disease status.

Gamma-glutamyl transferase to high-density lipoprotein cholesterol ratio is a more powerful marker than TyG index for predicting metabolic syndrome in patients with type 2 diabetes mellitus

Purpose

The prevalence of metabolic syndrome (MetS) is increasing globally and has become a global and national public health problem that cannot be ignored as an independent predictor of cardiovascular events, cancer and all-cause mortality. γ-glutamyl transferase (GGT) and high-density lipoprotein cholesterol (HDL-C) are associated with insulin resistance, dyslipidemia and oxidative stress. This study was designed to explore the relationship and predictive performance between γ-glutamyl transferase high-density lipoprotein cholesterol ratio (GGT/HDL-C) and MetS.

Methods

This was a cross-sectional study. MetS was diagnosed from biochemical and anthropometric data in subjects with T2DM. Multivariate logistic regression was used to analyses the relationship between GGT/HDL-C ratio, TyG index and HOMA-IR and MetS in subjects with T2DM. Receiver operating characteristic (ROC) curve was drawn and the areas under the curve (AUC) were used to assess the ability of these indexes in screening MetS in subjects with T2DM. Statistical differences between the AUC values of these indexes were compared. In addition, we performed subgroup analyses and interactions.

Results

769 (70.55%) patients with T2DM were defined as having MetS. patients with MetS had higher anthropometric values and biochemical indicators compared to those without MetS. Multivariate logistic regression analysis of GGT/HDL-C ratio was an independent risk factor for MetS (Per 1 SD increase, OR = 2.49, 95% CI: 1.51, 4.10). According to ROC curve analysis, the value of GGT/HDL-C ratio in predicting MetS in subjects with T2DM was superior to that of TyG index and HOMA-IR. The best cut-off value for GGT/HDL-C prediction was 19.94.

Conclusions

GGT/HDL-C ratio may be an important predictor of MetS in subjects with T2DM, and its predictive power is stronger than that of TyG index and HOMA-IR. The risk of MetS in subjects with T2DM is increased in the presence of a higher GGT/HDL-C ratio.

Modulation of the Cellular microRNA Landscape: Contribution to the Protective Effects of High-Density Lipoproteins (HDL)

High-density lipoproteins (HDL) play an established role in protecting against cellular dysfunction in a variety of different disease contexts; however, harnessing this therapeutic potential has proved challenging due to the heterogeneous and relative instability of this lipoprotein and its variable cargo molecules. The purpose of this study is to examine the contribution of microRNA (miRNA; miR) sequences, either delivered directly or modulated endogenously, to these protective functions. This narrative review introduces the complex cargo carried by HDL, the protective functions associated with this lipoprotein, and the factors governing biogenesis, export and the uptake of microRNA. The possible mechanisms by which HDL can modulate the cellular miRNA landscape are considered, and the impact of key sequences modified by HDL is explored in diseases such as inflammation and immunity, wound healing, angiogenesis, dyslipidaemia, atherosclerosis and coronary heart disease, potentially offering new routes for therapeutic intervention.

Higher circulating levels of proneurotensin are associated with increased risk of incident NAFLD

BACKGROUND

Neurotensin (NT), an intestinal peptide able to promote fat absorption, is implicated in the pathogenesis of obesity. Increased levels of proneurotensin (pro-NT), a stable NT precursor fragment, have been found in subjects with nonalcoholic fatty liver disease (NAFLD); however, whether higher pro-NT levels are associated with an increased NAFLD risk independently of other metabolic risk factors is unsettled.

METHODS

Ultrasound-defined presence of NAFLD was assessed on 303 subjects stratified into tertiles according to fasting pro-NT levels. The longitudinal association between pro-NT levels and NAFLD was explored on the study participants without NAFLD at baseline reexamined after 5 years of follow-up (n = 124).

RESULTS

Individuals with higher pro-NT levels exhibited increased adiposity, a worse lipid profile, and insulin sensitivity as compared to the lowest tertile of pro-NT. Prevalence of NAFLD was progressively increased in the intermediate and highest pro-NT tertile as compared to the lowest tertile. In a logistic regression analysis adjusted for several confounders, individuals with higher pro-NT levels displayed a raised risk of having NAFLD (OR = 3.43, 95%CI = 1.48-7.97, p = 0.004) than those in the lowest pro-NT tertile. Within the study cohort without NAFLD at baseline, subjects with newly diagnosed NAFLD at follow-up exhibited higher baseline pro-NT levels than those without incident NAFLD. In a cox hazard regression analysis model adjusted for anthropometric and metabolic parameters collected at baseline and follow-up visit, higher baseline pro-NT levels were associated with an increased risk of incident NAFLD (HR = 1.52, 95%CI = 1.017-2.282, p = 0.04).

CONCLUSION

Higher pro-NT levels are a predictor of NAFLD independent of other metabolic risk factors.

Preserved Ratio Impaired Spirometry, Metabolomics, and the Risk of Type 2 Diabetes

CONTEXT

Whether baseline preserved ratio impaired spirometry (PRISm) is associated with the risk of developing type 2 diabetes (T2D) and if this association could be mediated by circulating metabolites remains to be elucidated.

OBJECTIVE

To measure the prospective association of PRISm with T2D and potential metabolic mediators thereof.

METHODS

This study used data from the UK Biobank and included 72 683 individuals without diabetes at baseline. PRISm was defined as the predicted forced expiratory volume in 1 second (FEV1) <80% and the FEV1/forced vital capacity ratio ≥0.70. Cox proportional hazards modeling was performed to assess the longitudinal relation between baseline PRISm and incident T2D. Mediation analysis was used to explore the mediation effects of circulating metabolites in the path from PRISm to T2D.

RESULTS

During a median follow-up of 12.06 years, 2513 participants developed T2D. Individuals who had PRISm (N = 8394) were 47% (95% CI, 33%-63%) more likely to develop T2D compared with those who had normal spirometry (N = 64 289). A total of 121 metabolites showed statistically significant mediation effects in the path from PRISm to T2D (false discovery rate <0.05). Glycoprotein acetyls, cholesteryl esters in large high-density lipoprotein (HDL), degree of unsaturation, cholesterol in large HDL, and cholesteryl esters in very large HDL were the top 5 metabolic markers, with mediation proportions (95% CI) being 11.91% (8.76%-16.58%), 11.04% (7.34%-15.55%), 10.36% (7.34%-14.71%), 9.87% (6.78%-14.09%), and 9.51% (6.33%-14.05%), respectively. A total of 11 principal components that explained 95% variance of the metabolic signatures accounted for 25.47% (20.83%-32.19%) of the relation between PRISm and T2D.

CONCLUSIONS

Our study revealed the association of PRISm with T2D risk and the potential roles of circulating metabolites in mediating this association.

Associations of the HOMA2-%B and HOMA2-IR with progression to diabetes and glycaemic deterioration in young and middle-aged Chinese

AIMS

Insulin deficiency (ID) and resistance (IR) contribute to progression from normal glucose tolerance to diabetes to insulin requirement although their relative contributions in young-onset diabetes is unknown.

METHODS

We examined the associations of HOMA2 using fasting plasma glucose and C-peptide in Chinese aged 20-50 years with (1) progression to type 2 diabetes (T2D) in participants without diabetes in a community-based cohort (1998-2013) and (2) glycaemic deterioration in patients with T2D in a clinic-based cohort (1995-2014). We defined ID as HOMA2-%B below median and insulin IR as HOMA2-IR above median.

RESULTS

During 10-year follow-up, 62 (17.9%) of 347 community-dwelling participants progressed to T2D. After 8.6 years, 291 (48.1%) of 609 patients with T2D had glycaemic deterioration. At baseline, progressors for T2D had higher HOMA2-IR, while in patients with T2D, progressors for glycaemic deterioration had higher HOMA2-IR and lower HOMA2-%B than non-progressors. The non-ID/IR group and the ID/IR group had an adjusted odds ratios of 2.47 (95% CI: 1.28, 4.94) and 5.36 (2.26, 12.79), respectively, for incident T2D versus the ID/non-IR group. In patients with T2D, 50% of the ID/IR group required insulin at 6.7 years versus around 11 years in the non-ID/IR or ID/non-IR, and more than 15 years in the non-ID/non-IR group. Compared with the latter group, the adjusted hazard ratios were 2.74 (1.80, 4.16) in the ID/non-IR, 2.73 (1.78, 4.19) in the non-ID/IR and 4.46 (2.87, 6.91) in the ID/IR group (p-interaction = 0.049).

CONCLUSIONS

In young Chinese adults, IR and ID contributed to progression to T2D and glycaemic deterioration.

Oral fat tolerance testing identifies abnormal pancreatic β-cell function and insulin resistance in individuals with normal glucose tolerance

AIMS/INTRODUCTION

Insulin sensitivity and β-cell function are affected by lipid metabolism disorders, even before the onset of type 2 diabetes. People are in the postprandial state most of the time. Therefore, identifying postprandial hyperlipemia is important. This study aimed to assess patients with abnormalities in lipid metabolism, but with normal glucose tolerance, using oral fat tolerance testing (OFTT) to identify defects in insulin sensitivity and β-cell function.

MATERIALS AND METHODS

We included 248 volunteers with normal glucose tolerance who underwent OFTT. They were divided into three groups in accordance with their fasting and 4-h postprandial triglyceride (TG) concentrations. Their lipid concentrations during OFTT were compared. The disposition index (DI) was applied to estimate β-cell function, and the Matsuda insulin sensitivity index (ISI_M ) was used to assess insulin sensitivity. We used multiple linear regression analysis to estimate the relationships of fasting and postprandial TG concentrations with β-cell function and insulin sensitivity .

RESULTS

The changes in TG concentrations during OFTT were more marked than those in low-density lipoprotein-cholesterol, high-density lipoprotein-cholesterol or total cholesterol concentrations. As lipid metabolism deteriorated, the ISI_M and the DI gradually decreased. Multiple linear regression analysis showed that fasting and 4-h postprandial TG concentrations affected LnISI_M and LnDI.

CONCLUSIONS

In individuals with normal glucose tolerance, β-cell function and insulin sensitivity gradually decrease with a deterioration in the lipid profile. Not only fasting TG, but also postprandial TG concentrations are independent risk factors for impaired β-cell function and insulin resistance.

The Emerging Role of the Gut Microbiome in Cardiovascular Disease: Current Knowledge and Perspectives

The collection of normally non-pathogenic microorganisms that mainly inhabit our gut lumen shapes our health in many ways. Structural and functional perturbations in the gut microbial pool, known as “dysbiosis”, have been proven to play a vital role in the pathophysiology of several diseases, including cardiovascular disease (CVD). Although therapeutic regimes are available to treat this group of diseases, they have long been the main cause of mortality and morbidity worldwide. While age, sex, genetics, diet, tobacco use, and alcohol consumption are major contributors (World Health Organization, 2018), they cannot explain all of the consequences of CVD. In addition to the abovementioned traditional risk factors, the constant search for novel preventative and curative tools has shed light on the involvement of gut bacteria and their metabolites in the pathogenesis of CVD. In this narrative review, we will discuss the established interconnections between the gut microbiota and CVD, as well as the plausible therapeutic perspectives.

Gamma-glutamyl transferase to high-density lipoprotein cholesterol ratio: A valuable predictor of type 2 diabetes mellitus incidence

BACKGROUND

Gamma-glutamyl transferase (GGT) and high-density lipoprotein cholesterol (HDL-C) have been proven to be valuable predictors of type 2 diabetes mellitus (T2DM). The aim of this study was to investigate the association between GGT/HDL-C ratio and incident T2DM.

METHODS

The study retrospectively analyzed 15453 participants from 2004 to 2015. Cox proportional hazards regression models and Kaplan-Meier curves were used to elucidate the effect of GGT/HDL-C ratio on T2DM. Restricted cubic spline (RCS) analysis was performed to explore any non-linear correlation between GGT/HDL-C ratio and the risk of T2DM. The predictive performance of GGT, HDL-C and GGT/HDL-C ratio for T2DM was evaluated utilizing receiver-operating-characteristic (ROC) curves.

RESULTS

During a median follow-up of 5.39 years, 373 cases of incident T2DM were observed. Kaplan-Meier curves showed that the cumulative probabilities of T2DM increased in the participants with higher GGT/HDL-C ratio significantly (P < 0.001). Cox models further clarified that high GGT/HDL-C ratio was an independent risk factor for T2DM (HR = 1.01, 95% CI = 1.00-1.01, P = 0.011). Linear positive correlation between GGT/HDL-C ratio and the risk of T2DM was demonstrated through RCS analysis. In the ROC analysis, GGT/HDL-C ratio (AUC = 0.75, 95% CI = 0.73-0.77) showed competitive role in the prediction of T2DM compared with single GGT and HDL-C.

CONCLUSIONS

The GGT/HDL-C ratio could serve as a valuable predictor of T2DM, and the risk of T2DM increases in the condition of higher GGT/HDL-C ratio.

Association between high-density lipoprotein cholesterol and type 2 diabetes mellitus among Chinese: the Beijing longitudinal study of aging

Background

Some previous studies on different populations have yielded inconsistent findings with respect to the relationship between levels of high-density lipoprotein cholesterol (HDL-C) and future type 2 diabetes mellitus (T2DM) incidence. This study was designed to gain further insight into this relationship through a cohort study with a 25-year follow-up duration.

Methods

In total, 1462 individuals that were 55 years of age or older and were free of T2DM at baseline were enrolled in the present study. T2DM incidence among this study population was detected through self-reported diagnoses or the concentration of fasting plasma glucose. The data were derived from nine surveys conducted from 1992 to 2017. The correlation between HDL-C levels and the T2DM risk was assessed through Cox proportional-hazards model and proportional hazards model for the sub-distribution with time-dependent variables.

Results

Over the follow-up period, 120 participants were newly diagnosed with new-onset T2DM. When research participants were separated into four groups on the basis for quartiles of their levels of HDL-C measured at baseline, and incidence of diabetes declined with higher baseline HDL-C levels at 12.60, 9.70, 5.38, and 5.22 per 1000 person-years, respectively. Adjusted hazard ratios (HRs) were 0.98 (95% confidence interval [CI]: 0.62–1.55), 0.48 (95% CI: 0.27–0.85) and 0.44 (95% CI: 0.25–0.80) for individuals with HDL-C levels within the 1.15–1.39, 1.40–1.69, and ≥ 1.70 mmol/L ranges relative to participants with HDL-C levels < 1.15 mmol/L. Multiple sensitivity analyses similarly revealed reduced risk of diabetes incidence with increased HDL-C levels. Incorporating the levels of HDL-C into a multivariate model significantly enhanced the overall power of the predictive model (P values were 0.0296, 0.0011, respectively, for 5- and 10-year risk of diabetes).

Conclusions

Levels of HDL-C were independently and negatively associated with the risk of the new-onset T2DM among middle-aged and elderly Chinese.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12944-021-01499-5.

MicroRNA Sequences Modulated by Beta Cell Lipid Metabolism: Implications for Type 2 Diabetes Mellitus

Alterations in lipid metabolism within beta cells and islets contributes to dysfunction and apoptosis of beta cells, leading to loss of insulin secretion and the onset of type 2 diabetes. Over the last decade, there has been an explosion of interest in understanding the landscape of gene expression which influences beta cell function, including the importance of small non-coding microRNA sequences in this context. This review sought to identify the microRNA sequences regulated by metabolic challenges in beta cells and islets, their targets, highlight their function and assess their possible relevance as biomarkers of disease progression in diabetic individuals. Predictive analysis was used to explore networks of genes targeted by these microRNA sequences, which may offer new therapeutic strategies to protect beta cell function and delay the onset of type 2 diabetes.

Protection against Glucolipotoxicity by High Density Lipoprotein in Human PANC-1 Hybrid 1.1B4 Pancreatic Beta Cells: The Role of microRNA

High-density lipoproteins provide protection against the damaging effects of glucolipotoxicity in beta cells, a factor which sustains insulin secretion and staves off onset of type 2 diabetes mellitus. This study examines epigenetic changes in small non-coding microRNA sequences induced by high density lipoproteins in a human hybrid beta cell model, and tests the impact of delivery of a single sequence in protecting against glucolipotoxicity. Human PANC-1.1B4 cells were used to establish Bmax and Kd for [³H]cholesterol efflux to high density lipoprotein, and minimum concentrations required to protect cell viability and reduce apoptosis to 30mM glucose and 0.25 mM palmitic acid. Microchip array identified the microRNA signature associated with high density lipoprotein treatment, and one sequence, hsa-miR-21-5p, modulated via delivery of a mimic and inhibitor. The results confirm that low concentrations of high-density lipoprotein can protect against glucolipotoxicity, and report the global microRNA profile associated with this lipoprotein; delivery of miR-21-5p mimic altered gene targets, similar to high density lipoprotein, but could not provide sufficient protection against glucolipotoxicity. We conclude that the complex profile of microRNA changes due to HDL treatment may be difficult to replicate using a single microRNA, findings which may inform current drug strategies focused on this approach.

The effect of probiotics, prebiotics or synbiotics on metabolic outcomes in individuals with diabetes: a systematic review and meta-analysis

AIMS/HYPOTHESIS

The aim was to conduct a systematic review and meta-analysis of randomised controlled clinical trials assessing the effect of probiotic, prebiotic or synbiotic supplementation on gut microbiota and glucose control and lipid levels in individuals with diabetes.

METHODS

MEDLINE, EMBASE and the Cochrane Library were searched. The eligibility criteria for the studies was involvement of participants with a diagnosis of type 1 or type 2 diabetes. Metabolic outcomes (glucose control, insulinaemia, and lipid profile) of any probiotic, prebiotic or synbiotic supplementation related to modification of gut microbiota (prebiotics, probiotics and synbiotics) were analysed. We provided a narrative synthesis and meta-analysis of the findings on metabolic outcomes from the studies. Metabolic outcomes were extracted post-intervention and expressed as mean differences (MDs) and 95% CIs between treatment and comparator groups. We pooled the results using a random-effects meta-analysis. The meta-analysis was conducted using Review Manager (RevMan) software.

RESULTS

After the removal of duplicates and ineligible studies, 5219 studies were retained for review of titles and abstracts. The number of articles was reduced to 130 by review, for which the full-text articles were obtained and reassessed, 38 of which were included in the final meta-analysis. Overall, the use of prebiotics, probiotics or synbiotics reduced HbA_1c levels, but did not reach the threshold for significance (-2.17 mmol/mol, 95% CI -4.37, 0.03; p = 0.05, [-0.20%, 95% CI -0.40 to 0.00; p = 0.05, I² = 66%]) and had no effect on LDL-cholesterol levels (-0.05 mmol/l; 95% CI -0.14, 0.05, p = 0.35, I² = 37%). However, their consumption decreased levels of fasting blood glucose (-0.58 mmol/l; 95% CI -0.86, -0.30; p < 0.01, I² = 60%), total cholesterol (-0.14 mmol/l; 95% CI -0.26, -0.02, p = 0.02, I² = 39%), triacylglycerols (-0.11 mmol/l; 95% CI -0.20, -0.02, p = 0.01, I²= 21%) and insulinaemia (-10.51 pmol/l; 95% CI -16.68,-4.33, p < 0.01, I² = 74%), and increased HDL-cholesterol levels (0.04 mmol/l; 95% CI 0.01, 0.07, p < 0.01, I²= 24%).

CONCLUSIONS/INTERPRETATION

In individuals with diabetes mellitus, supplementation with probiotics, prebiotics or synbiotics improved metabolic variables, although the magnitude of this effect is low. Our results suggest that consumption of probiotics, prebiotics or synbiotics may be a potential adjuvant treatment for improving metabolic outcomes.

REGISTRATION

PROSPERO ID CRD42017080071. Graphical abstract.

Relative Risk of Cardiovascular Disease Is Higher in Women With Type 2 Diabetes, but Not in Those With Prediabetes, as Compared With Men

OBJECTIVE

Most but not all studies suggest that women with type 2 diabetes have higher relative risk (RR) for cardiovascular disease (CVD) than men. More uncertainty exists on whether the RR for CVD is higher in women with prediabetes compared with men with prediabetes.

RESEARCH DESIGN AND METHODS

In a cross-sectional study, in 3,540 adults with normal glucose tolerance (NGT), prediabetes, and diabetes, we compared the RR for prevalent nonfatal CVD between men and women. In a longitudinal study including 1,658 adults with NGT, prediabetes, and diabetes, we compared the RR for incidences of major adverse outcomes, including all-cause death, coronary heart disease, and cerebrovascular disease events, after 5.6 years of follow-up.

RESULTS

Women with prediabetes and diabetes exhibited greater relative differences in BMI, waist circumference, blood pressure, total cholesterol, LDL cholesterol, HDL cholesterol, triglycerides, fasting glucose, hs-CRP, and white blood cell count than men with prediabetes and diabetes when compared with their NGT counterparts. We found a higher RR for prevalent CVD in women with diabetes (RR 9.29; 95% CI 4.73-18.25; P < 0.0001) than in men (RR 4.56; 95% CI 3.07-6.77; P < 0.0001), but no difference in RR for CVD was observed comparing women and men with prediabetes. In the longitudinal study, we found that women with diabetes, but not those with prediabetes, have higher RR (RR 5.25; 95% CI 3.22-8.56; P < 0.0001) of incident major adverse outcomes than their male counterparts (RR 2.72; 95% CI 1.81-4.08; P < 0.0001).

CONCLUSIONS

This study suggests that women with diabetes, but not those with prediabetes, have higher RR for prevalent and incident major adverse outcomes than men.

HDL (High-Density Lipoprotein) and ApoA-1 (Apolipoprotein A-1) Potentially Modulate Pancreatic α-Cell Glucagon Secretion

OBJECTIVE

Subjects with low levels of HDL (high-density lipoprotein) and ApoA-1 (apolipoprotein A-1) have increased risk to develop type 2 diabetes. HDL levels are an independent predictor of β-cell function and positively modulate it. Type 2 diabetes is characterized by defects in both β and α-cell function, but the effect of HDL and ApoA1 on α-cell function is unknown. Approach and Results: We observed a significant negative correlation (r=-0.422, P<0.0001) between HDL levels and fasting glucagon in a cohort of 132 Italian subjects. In a multivariable regression analysis including potential confounders such as age, sex, BMI, triglycerides, total cholesterol, fasting and 2-hour postload glucose, and fasting insulin, the association between HDL and fasting glucagon remained statistically significant (β=-0.318, P=0.006). CD1 mice treated with HDL or ApoA-1 for 3 consecutive days showed a 32% (P<0.001) and 23% (P<0.05) reduction, respectively, in glucagon levels following insulin-induced hypoglycemia, compared with controls. Treatment of pancreatic αTC1 clone 6 cells with HDL or ApoA-1 for 24 hours resulted in a significant reduction of glucagon expression (P<0.04) and secretion (P<0.01) after an hypoglycemic stimulus and increased Akt (RAC-alpha serine/threonine-protein kinase) and FoxO1 (forkhead/winged helix box gene, group O-1) phosphorylation. Pretreatment with Akt inhibitor VIII, PI3K (phosphatidylinositol 3-kinase) inhibitor LY294002, and HDL receptor SCARB-1 (scavenger receptor class B type 1) inhibitor BLT-1 (block lipid transport-1) restored αTC1 cell response to low glucose levels.

CONCLUSIONS

These results support the notion that HDL and ApoA-1 modulate glucagon expression and secretion by binding their cognate receptor SCARB-1, and activating the PI3K/Akt/FoxO1 signaling cascade in an in vitro α-cell model. Overall, these results raise the hypothesis that HDL and ApoA-1 may have a role in modulating glucagon secretion.

A short peptide of the C-terminal class Y helices of apolipoprotein A-I has preserved functions in cholesterol efflux and in vivo metabolic control

Apolipoprotein A-I (ApoA-I) of high-density lipoprotein (HDL) induces glucose uptake by muscle tissues and stimulates pancreatic insulin secretion, and also facilitates cholesterol transport in circulation, and is explored for anti-diabetic and anti-atherosclerotic treatments. As the better alternative to complex protein-lipid formulations it was recently established that the C-terminal region of the ApoA-I protein singly improves the metabolic control and prevents formation of atherosclerotic plaques. Additional investigations of peptides based on the ApoA-I structure may lead to novel anti-diabetic drugs. We here investigate a short peptide (33mer, RG33) that corresponds to the two last helical segments (aa 209-241) of the ApoA-I structure (so-called class Y-helices which forms amphipathic helices) for stability and solubility in serum, for in vitro cholesterol efflux capability, and for providing in vivo glucose control in an insulin resistant mouse model. The RG33 peptide efficiently solubilizes lipid-vesicles, and promotes the efflux of cholesterol from cultured macrophages. The efflux capacity is significantly increased in the presence of lipids compared to non-lipidated RG33. Finally, acute treatment with the RG33 peptide significantly improves the glucose clearance capacity of insulin resistant mice. The impact of the RG33 peptide on glucose control and cholesterol transport, as well as the physicochemical properties, makes it a good candidate for translational exploration of its therapeutic potential in diabetes treatment.