Relationship of apolipoprotein C-III proteoform composition with ankle-brachial index and peripheral artery disease in the Multi-Ethnic Study of Atherosclerosis (MESA).

BACKGROUND AND AIMS: Apolipoprotein C-III (apoC-III) proteoform composition shows distinct relationships with plasma lipids and cardiovascular risk. The present study tested whether apoC-III proteoforms are associated with risk of peripheral artery disease (PAD). METHODS: ApoC-III proteoforms, i.e., native (C-III0a), and glycosylated with zero (C-III0b), one (C-III1) or two (C-III2) sialic acids, were measured by mass spectrometry immunoassay on 5,734 Multi-Ethnic Study of Atherosclerosis participants who were subsequently followed for clinical PAD over 17 years. Ankle-brachial index (ABI) was also assessed at baseline and then 3 and 10 years later in 4,830 participants. RESULTS: Higher baseline C-III0b/C-III1 and lower baseline C-III2/C-III1 were associated with slower decline in ABI (follow-up adjusted for baseline) over time, independently of cardiometabolic risk factors, and plasma triglycerides and HDL cholesterol levels (estimated difference per 1 SD was 0.31 % for both, p < 0.01). The associations between C-III2/C-III1 and changes in ABI were stronger in men (-1.21 % vs. -0.27 % in women), and in Black and Chinese participants (-0.83 % and -0.86 % vs. 0.12 % in White). Higher C-III0b/C-III1 was associated with a trend for lower risk of PAD (HR = 0.84 [95%CI: 0.67-1.04]) that became stronger after excluding participants on lipid-lowering medications (0.73 [95%CI: 0.57-0.94]). Neither change in ABI nor clinical PAD was related to total apoC-III levels. CONCLUSIONS: We found associations of apoC-III proteoform composition with changes in ABI that were independent of other risk factors, including plasma lipids. Our data further support unique properties of apoC-III proteoforms in modulating vascular health that go beyond total apoC-III levels.

Elevated apolipoprotein C3 augments diabetic kidney disease and associated atherosclerosis in type 2 diabetes.

Diabetes increases the risk of both cardiovascular disease and kidney disease. Notably, most of the excess cardiovascular risk in people with diabetes is in those with kidney disease. Apolipoprotein C3 (APOC3) is a key regulator of plasma triglycerides, and it has recently been suggested to play a role in both type 1 diabetes-accelerated atherosclerosis and kidney disease progression. To investigate if APOC3 plays a role in kidney disease in people with type 2 diabetes, we analyzed plasma levels of APOC3 from the Veterans Affairs Diabetes Trial. Elevated baseline APOC3 levels predicted a greater loss of renal function. To mechanistically test if APOC3 plays a role in diabetic kidney disease and associated atherosclerosis, we treated black and tan, brachyury, WT and leptin-deficient (OB; diabetic) mice, a model of type 2 diabetes, with an antisense oligonucleotide (ASO) to APOC3 or a control ASO, all in the setting of human-like dyslipidemia. Silencing APOC3 prevented diabetes-augmented albuminuria, renal glomerular hypertrophy, monocyte recruitment, and macrophage accumulation, partly driven by reduced ICAM1 expression. Furthermore, reduced levels of APOC3 suppressed atherosclerosis associated with diabetes. This suggests that targeting APOC3 might benefit both diabetes-accelerated atherosclerosis and kidney disease.

Association of Both Short-term and Long-term Glycemic Variability With the Development of Microalbuminuria in the ACCORD Trial.

Both long- and short-term glycemic variability have been associated with incident diabetes complications. We evaluated their relative and potential additive effects on incident renal complications in the Action to Control Cardiovascular Risk in Diabetes trial. A marker of short-term glycemic variability, 1,5-anhydroglucitol (1,5-AG), was measured in 4,000 random 12-month postrandomization plasma samples (when hemoglobin A1c [HbA1c] was stable). Visit-to-visit fasting plasma glucose coefficient of variation (CV-FPG) was determined from 4 months postrandomization until the end point of microalbuminuria or macroalbuminuria. Using Cox proportional hazards models, high CV-FPG and low 1,5-AG were independently associated with microalbuminuria after adjusting for clinical risk factors. However, only the CV-FPG association remained after additional adjustment for average HbA1c. Only CV-FPG was a significant risk factor for macroalbuminuria. This post hoc analysis indicates that long-term rather than short-term glycemic variability better predicts the risk of renal disease in type 2 diabetes. ARTICLE HIGHLIGHTS: The relative and potential additive effects of long- and short-term glycemic variability on the development of diabetic complications are unknown. We aimed to assess the individual and combined relationships of long-term visit-to-visit glycemic variability, measured as the coefficient of variation of fasting plasma glucose, and short-term glucose fluctuation, estimated by the biomarker 1,5-anhydroglucitol, with the development of proteinuria. Both estimates of glycemic variability were independently associated with microalbuminuria, but only long-term glycemic variability remained significant after adjusting for average hemoglobin A1c. Our findings suggest that longer-term visit-to-visit glucose variability improves renal disease prediction in type 2 diabetes.

Association of apolipoproteins C-I and C-II truncations with coronary heart disease and progression of coronary artery calcium: Multi-Ethnic Study of Atherosclerosis.

BACKGROUND AND AIMS: Higher truncated-to-native proteoform ratios of apolipoproteins (apo) C-I (C-I'/C-I) and C-II (C-II'/C-II) are associated with less atherogenic lipid profiles. We examined prospective relationships of C-I'/C-II and C-II'/C-II with coronary heart disease (CHD) and coronary artery calcium (CAC). METHODS: ApoC-I and apoC-II proteoforms were measured by mass spectrometry immunoassay in 5790 MESA baseline plasma samples. CHD events (myocardial infarction, resuscitated cardiac arrest, fatal CHD, n = 434) were evaluated for up to 17 years. CAC was measured 1-4 times over 10 years for incident CAC (if baseline CAC = 0), and changes (follow-up adjusted for baseline) in CAC score and density (if baseline CAC>0). RESULTS: C-II'/C-II was inversely associated with CHD (n = 434 events) after adjusting for non-lipid cardiovascular risk factors (Hazard ratio: 0.89 [95% CI: 0.81-0.98] per SD), however, the association was attenuated after further adjustment for HDL levels (0.93 [0.83-1.03]). There was no association between C-I'/C-I and CHD (0.98 [0.88-1.08]). C-II'/C-II was positively associated with changes in CAC score (3.4% [95%CI: 0.6, 6.3]) and density (6.3% [0.3, 4.2]), while C-I'/C-I was inversely associated with incident CAC (Risk ratio: 0.89 [95% CI: 0.81, 0.98]) in fully adjusted models that included plasma lipids. Total apoC-I and apoC-II concentrations were not associated with CHD, incident CAC or change in CAC score. CONCLUSIONS: Increased apoC-II truncation was associated with reduced CHD, possibly explained by differences in lipid metabolism. Increased apoC-I and apoC-II truncations were also associated with less CAC progression and/or development of denser coronary plaques.

Apo CIII Proteoforms, Plasma Lipids, and Cardiovascular Risk in MESA.

BACKGROUND: Apo CIII (apolipoprotein CIII) is an important regulator of triglyceride metabolism and was associated with cardiovascular risk in several cohorts. It is present in 4 major proteoforms, a native peptide (CIII0a), and glycosylated proteoforms with zero (CIII0b), 1 (CIII1, most abundant), or 2 (CIII2) sialic acids, which may differentially modify lipoprotein metabolism. We studied the relationships of these proteoforms with plasma lipids and cardiovascular risk. METHODS: Apo CIII proteoforms were measured by mass spectrometry immunoassay in baseline plasma samples of 5791 participants of Multi-Ethnic Study of Atherosclerosis, an observational community-based cohort. Standard plasma lipids were collected for up to 16 years and cardiovascular events (myocardial infarction, resuscitated cardiac arrest, or stroke) were adjudicated for up to 17 years. RESULTS: Apo CIII proteoform composition differed by age, sex, race and ethnicity, body mass index, and fasting glucose. Notably, CIII1 was lower in older participants, men and Black and Chinese (versus White) participants, and higher in obesity and diabetes. In contrast, CIII2 was higher in older participants, men, Black, and Chinese persons, and lower in Hispanic individuals and obesity. Higher CIII2 to CIII1 ratio (CIII2/III1) was associated with lower triglycerides and higher HDL (high-density lipoprotein) in cross-sectional and longitudinal models, independently of clinical and demographic risk factors and total apo CIII. The associations of CIII0a/III1 and CIII0b/III1 with plasma lipids were weaker and varied through cross-sectional and longitudinal analyses. Total apo CIII and CIII2/III1 were positively associated with cardiovascular disease risk (n=669 events, hazard ratios, 1.14 [95% CI, 1.04-1.25] and 1.21 [1.11-1.31], respectively); however, the associations were attenuated after adjustment for clinical and demographic characteristics (1.07 [0.98-1.16]; 1.07 [0.97-1.17]). In contrast, CIII0b/III1 was inversely associated with cardiovascular disease risk even after full adjustment including plasma lipids (0.86 [0.79-0.93]). CONCLUSIONS: Our data indicate differences in clinical and demographic relationships of apo CIII proteoforms, and highlight the importance of apo CIII proteoform composition in predicting future lipid patterns and cardiovascular disease risk.

Plasma proteoforms of apolipoproteins C-I and C-II are associated with plasma lipids in the Multi-Ethnic Study of Atherosclerosis.

Apolipoproteins (apo) C-I and C-II are key regulators of triglyceride and HDL metabolism. Both exist as full-size native and truncated (apoC-I'; apoC-II') posttranslational proteoforms. However, the determinants and the role of these proteoforms in lipid metabolism are unknown. Here, we measured apoC-I and apoC-II proteoforms by mass spectrometry immunoassay in baseline and 10-year follow-up plasma samples from the Multi-Ethnic Study of Atherosclerosis. We found that baseline total apoC-I (mean = 9.2 mg/dl) was lower in African Americans (AA), Chinese Americans (CA), and Hispanics (by 1.8; 1.0; 1.0 mg/dl vs. whites), higher in women (by 1.2 mg/dl), and positively associated with plasma triglycerides and HDL. Furthermore, we observed that the truncated-to-native apoC-I ratio (apoC-I'/C-I) was lower in CA, negatively associated with triglycerides, and positively associated with HDL. We determined that total apoC-II (8.8 mg/dl) was lower in AA (by 0.8 mg/dl) and higher in CA and Hispanics (by 0.5 and 0.4 mg/dl), positively associated with triglycerides, and negatively associated with HDL. In addition, apoC-II'/C-II was higher in AA and women, negatively associated with triglycerides, and positively associated with HDL. We showed that the change in triglycerides was positively associated with changes in total apoC-I and apoC-II and negatively associated with changes in apoC-I'/C-I and apoC-II'/C-II, whereas the change in HDL was positively associated with changes in total apoC-I and apoC-II'/C-II and negatively associated with change in total apoC-II. This study documents racial/ethnic variation in apoC-I and apoC-II plasma levels and highlights apolipoprotein posttranslational modification as a potential regulator of plasma lipids.

Advanced Glycation End Products Predict Loss of Renal Function and High-Risk Chronic Kidney Disease in Type 2 Diabetes.

OBJECTIVE: To evaluate the association of a multicomponent advanced glycation end product (AGE) panel with decline in kidney function and its utility in predicting renal function loss (RFL) when added to routine clinical measures in type 2 diabetes. RESEARCH DESIGN AND METHODS: Carboxymethyl and carboxyethyl lysine and methylglyoxal, 3-deoxyglucosone, and glyoxal hydroimidazolones were measured in baseline serum and plasma samples, respectively, from Action to Control Cardiovascular Risk in Diabetes (ACCORD) (n = 1,150) and Veterans Affairs Diabetes Trial (VADT) (n = 447) participants. A composite AGE score was calculated from individual AGE z scores. The primary outcome was a sustained 30% decline in estimated glomerular filtration rate (eGFR) (30% RFL in both cohorts). Secondary outcomes (in ACCORD) were 40% RFL, macroalbuminuria, and high-risk chronic kidney disease (hrCKD). RESULTS: After adjustment for baseline and follow-up HbA1c and other risk factors in ACCORD, the AGE score was associated with reduction in eGFR (ß-estimate -0.66 mL/min ⋅ 1.73 m2 per year; P = 0.001), 30% RFL (hazard ratio 1.42 [95% CI 1.13-1.78]; P = 0.003), 40% RFL (1.40 [1.13-1.74]; P = 0.003), macroalbuminuria (1.53 [1.13-2.06]; P = 0.006), and hrCKD (1.88 [1.37-2.57]; P < 0.0001). AGE score improved net reclassification (NRI) and relative integrated discrimination (IDI) for 30% RFL (NRI 23%; P = 0.02) (relative IDI 7%; P = 0.009). In VADT, the AGE score calculated by the ACCORD-derived coefficients was associated with 30% RFL (1.37 [1.03-1.82); P = 0.03) and improved NRI (24%; P = 0.03) but not IDI (P = 0.18). CONCLUSIONS: These data provide further support for a causal role of AGEs in diabetic nephropathy independently of glycemic control and suggest utility of the composite AGE panel in predicting long-term decline in renal function.

Association of low fasting C-peptide levels with cardiovascular risk, visit-to-visit glucose variation and severe hypoglycemia in the Veterans Affairs Diabetes Trial (VADT).

AIMS: Low C-peptide levels, indicating beta-cell dysfunction, are associated with increased within-day glucose variation and hypoglycemia. In advanced type 2 diabetes, severe hypoglycemia and increased glucose variation predict cardiovascular (CVD) risk. The present study examined the association between C-peptide levels and CVD risk and whether it can be explained by visit-to-visit glucose variation and severe hypoglycemia. MATERIALS AND METHODS: Fasting C-peptide levels at baseline, composite CVD outcome, severe hypoglycemia, and visit-to-visit fasting glucose coefficient of variation (CV) and average real variability (ARV) were assessed in 1565 Veterans Affairs Diabetes Trial participants. RESULTS: There was a U-shaped relationship between C-peptide and CVD risk with increased risk with declining levels in the low range (< 0.50 nmol/l, HR 1.30 [95%CI 1.05-1.60], p = 0.02) and with rising levels in the high range (> 1.23 nmol/l, 1.27 [1.00-1.63], p = 0.05). C-peptide levels were inversely associated with the risk of severe hypoglycemia (OR 0.68 [0.60-0.77]) and visit-to-visit glucose variation (CV, standardized beta-estimate - 0.12 [SE 0.01]; ARV, - 0.10 [0.01]) (p < 0.0001 all). The association of low C-peptide levels with CVD risk was independent of cardiometabolic risk factors (1.48 [1.17-1.87, p = 0.001) and remained associated with CVD when tested in the same model with severe hypoglycemia and glucose CV. CONCLUSIONS: Low C-peptide levels were associated with increased CVD risk in advanced type 2 diabetes. The association was independent of increases in glucose variation or severe hypoglycemia. C-peptide levels may predict future glucose control patterns and CVD risk, and identify phenotypes influencing clinical decision making in advanced type 2 diabetes.

Refining determinants of associations of visit-to-visit blood pressure variability with cardiovascular risk: results from the Action to Control Cardiovascular Risk in Diabetes Trial.

OBJECTIVES: As there is uncertainty about the extent to which baseline blood pressure level or cardiovascular risk modifies the relationship between blood pressure variability (BPv) and cardiovascular disease, we comprehensively examined the role of BPv in cardiovascular disease risk in the Action to Control Cardiovascular Risk in Diabetes (ACCORD) Trial. METHODS: Using data from ACCORD, we examined the relationship of BPv with development of the primary CVD outcome, major coronary heart disease (CHD), and total stroke using time-dependent Cox proportional hazards models. RESULTS: BPv was associated with the primary CVD outcome and major CHD but not stroke. The positive association with the primary CVD outcome and major CHD was more pronounced in low and high strata of baseline SBP (<120 and >140 mmHg) and DBP (<70 and >80 mmHg). The effect of BPv on CVD and CHD was more pronounced in those with both prior CVD history and low blood pressure. Dips, not elevations, in blood pressure appeared to drive these associations. The relationships were generally not attenuated by adjustment for mean blood pressure, medication adherence, or baseline comorbidities. A sensitivity analysis using CVD events from the long-term posttrial follow-up (ACCORDION) was consistent with the results from ACCORD. CONCLUSION: In ACCORD, the effect of BPv on adverse cardiovascular (but not cerebrovascular) outcomes is modified by baseline blood pressure and prior CVD. Recognizing these more nuanced relationships may help improve risk stratification and blood pressure management decisions as well as provide insight into potential underlying mechanisms.

The Effect of Exenatide Once Weekly on Carotid Atherosclerosis in Individuals With Type 2 Diabetes: An 18-Month Randomized Placebo-Controlled Study.

OBJECTIVE: Glucagon-like peptide 1 receptor agonists (GLP-1RAs) improved multiple proatherogenic risk factors and reduced cardiovascular events in recent clinical trials, suggesting that they may slow progression of atherosclerosis. We tested whether exenatide once weekly reduces carotid plaque progression in individuals with type 2 diabetes. RESEARCH DESIGN AND METHODS: In a double-blind, pragmatic trial, 163 participants were randomized (2:1) to exenatide (n = 109) or placebo (n = 54). Changes in carotid plaque volume and composition were measured at 9 and 18 months by multicontrast 3 Tesla MRI. Fasting and post-high-fat meal plasma glucose and lipids, and endothelial function responses, were measured at 3, 9, and 18 months. RESULTS: Exenatide reduced hemoglobin A1c (HbA1c) (estimated difference vs. placebo 0.55%, P = 0.0007) and fasting and postmeal plasma glucose (19 mg/dL, P = 0.0002, and 25 mg/dL, P < 0.0001, respectively). Mean (SD) change in plaque volume in the exenatide group (0.3% [2%]) was not different from that in the placebo group (-2.2% [8%]) (P = 0.4). The change in plaque volume in the exenatide group was associated with changes in HbA1c (r = 0.38, P = 0.0004), body weight, and overall plasma glucose (r = 0.29, P = 0.007 both). There were no differences in changes in plaque composition, body weight, blood pressure, fasting and postmeal plasma triglycerides, and endothelial function between the groups. CONCLUSIONS: Exenatide once weekly for up to 18 months improved fasting and postprandial glycemic control but did not modify change in carotid plaque volume or composition. This study raises the possibility that short-term antiatherosclerotic effects may not play a central role in the cardiovascular benefits of GLP-1RAs.

Fasting Glucose Variation Predicts Microvascular Risk in ACCORD and VADT.

AIMS: The association of glycemic variability with microvascular disease complications in type 2 diabetes (T2D) has been under-studied and remains unclear. We investigated this relationship using both Action to Control Cardiovascular Risk in Diabetes (ACCORD) and the Veteran Affairs Diabetes Trial (VADT). METHODS: In ACCORD, fasting plasma glucose (FPG) was measured 1 to 3 times/year for up to 84 months in 10 251 individuals. In the VADT, FPG was measured every 3 months for up to 87 months in 1791 individuals. Variability measures included coefficient of variation (CV) and average real variability (ARV) for fasting glucose. The primary composite outcome was time to either severe nephropathy or retinopathy event and secondary outcomes included each outcome individually. To assess the association, we considered variability measures as time-dependent covariates in Cox proportional hazard models. We conducted a meta-analysis across the 2 trials to estimate the risk of fasting glucose variability as well as to assess the heterogenous effects of FPG variability across treatment arms. RESULTS: In both ACCORD and the VADT, the CV and ARV of FPG were associated with development of future microvascular outcomes even after adjusting for other risk factors, including measures of average glycemic control (ie, cumulative average of HbA1c). Meta-analyses of these 2 trials confirmed these findings and indicated FPG variation may be more harmful in those with less intensive glucose control. CONCLUSIONS: This post hoc analysis indicates that variability of FPG plays a role in, and/or is an independent and readily available marker of, development of microvascular complications in T2D.

Blood Pressure Variability and Risk of Heart Failure in ACCORD and the VADT.

OBJECTIVE: Although blood pressure variability is increasingly appreciated as a risk factor for cardiovascular disease, its relationship with heart failure (HF) is less clear. We examined the relationship between blood pressure variability and risk of HF in two cohorts of type 2 diabetes participating in trials of glucose and/or other risk factor management. RESEARCH DESIGN AND METHODS: Data were drawn from the Action to Control Cardiovascular Risk in Diabetes (ACCORD) trial and the Veterans Affairs Diabetes Trial (VADT). Coefficient of variation (CV) and average real variability (ARV) were calculated for systolic (SBP) and diastolic blood pressure (DBP) along with maximum and cumulative mean SBP and DBP during both trials. RESULTS: In ACCORD, CV and ARV of SBP and DBP were associated with increased risk of HF, even after adjusting for other risk factors and mean blood pressure (e.g., CV-SBP: hazard ratio [HR] 1.15, P = 0.01; CV-DBP: HR 1.18, P = 0.003). In the VADT, DBP variability was associated with increased risk of HF (ARV-DBP: HR 1.16, P = 0.001; CV-DBP: HR 1.09, P = 0.04). Further, in ACCORD, those with progressively lower baseline blood pressure demonstrated a stepwise increase in risk of HF with higher CV-SBP, ARV-SBP, and CV-DBP. Effects of blood pressure variability were related to dips, not elevations, in blood pressure. CONCLUSIONS: Blood pressure variability is associated with HF risk in individuals with type 2 diabetes, possibly a consequence of periods of ischemia during diastole. These results may have implications for optimizing blood pressure treatment strategies in those with type 2 diabetes.

Glycaemic variation is a predictor of all-cause mortality in the Veteran Affairs Diabetes Trial.

Diabetes is associated with substantially increased mortality. Classic risk factors explain a portion of the excess of mortality in type 2 diabetes. The aim of this study was to examine whether visit-to-visit variation in fasting glucose and haemoglobin A1c values in the Veteran Affairs Diabetes Trial were associated with all-cause mortality in patients with type 2 diabetes in addition to other comorbidity conditions, hypoglycaemic events and adverse lifestyle behaviours. The Veteran Affairs Diabetes Trial was a randomized trial that enrolled 1791 military veterans who had a suboptimal response to therapy for type 2 diabetes to receive either intensive or standard glucose control. During the Veteran Affairs Diabetes Trial, fasting glucose and haemoglobin A1c were measured quarterly for up to 84 months. Variability measures included coefficient of variation and average real variability. We found that variability measures (coefficient of variation and average real variability) of fasting glucose were predictors of all-cause mortality, even after adjusting for comorbidity index, mean fasting glucose and adverse lifestyle behaviour during the study. Accounting for severe hypoglycaemia did not weaken this association. Our analysis indicates that in the Veteran Affairs Diabetes Trial, longitudinal variation in fasting glucose was associated with all-cause mortality, even when accounting for standard measures of glucose control as well as comorbidity and lifestyle factors.

Advanced Glycation End Products, Oxidation Products, and Incident Cardiovascular Events in Patients With Type 2 Diabetes.

OBJECTIVE: The goal of this study was to determine whether plasma levels of advanced glycation end products (AGE) and oxidation products (OP) predict the incidence of cardiovascular disease (CVD) in type 2 diabetes. RESEARCH DESIGN AND METHODS: Five specific AGE (methylglyoxal hydroimidazolone, carboxymethyl lysine, carboxyethyl lysine, 3-deoxyglucosone hydroimidazolone, and glyoxal hydroimidazolone) and two OP (2-aminoadipic acid and methionine sulfoxide [MetSO]) were measured at baseline in two intensive glucose-lowering studies: 1) a subcohort of the Veterans Affairs Diabetes Trial (VADT) (n = 445) and 2) a nested case-control subgroup from the Action to Control Cardiovascular Risk in Diabetes (ACCORD) study (n = 271). RESULTS: Increased levels of several AGE and OP were associated with older age, decreased kidney function, previous CVD, and longer diabetes duration, but not with hemoglobin A1c. In the VADT, increased risk of incident CVD events (n = 107) was associated with lower MetSO after adjusting for age, race/ethnicity, sex, prior CVD event, kidney function, treatment assignment, and diabetes duration (hazard ratio [HR] 0.53; 95% CI 0.28-0.99; P = 0.047). Individuals with both low MetSO and high 3-deoxyglucosone hydroimidazolone concentrations were at highest risk for CVD (HR 1.70; P = 0.01). In the ACCORD study, those with incident CVD events (n = 136) had lower MetSO (by 14%; P = 0.007) and higher glyoxal hydroimidazolone and carboxymethyl lysine (by 18% and 15%, respectively; P = 0.04 for both); however, only the difference in MetSO remained significant after adjustment for prior CVD event (P = 0.002). CONCLUSIONS: Lower levels of MetSO and higher levels of select AGE are associated with increased incident CVD and may help account for the limited benefit of intensive glucose lowering in type 2 diabetes.

Effect of liraglutide on dietary lipid-induced insulin resistance in humans.

AIMS: To test whether liraglutide suppresses postprandial elevations in lipids and thus protects against high saturated fatty acid (SFA) diet-induced insulin resistance. METHODS: In a randomized placebo-controlled crossover study, 32 participants with normal or mildly impaired glucose tolerance received liraglutide and placebo for 3 weeks each. Insulin suppression tests (IST) were conducted at baseline and after a 24-hour SFA-enriched diet after each treatment. Plasma glucose, insulin, triglycerides and non-esterified fatty acids (NEFA) were measured over the initial 8 hours (breakfast and lunch) on the SFA diet. A subset of participants underwent ex vivo measurements of insulin-mediated vasodilation of adipose tissue arterioles and glucose metabolism regulatory proteins in skeletal muscle. RESULTS: Liraglutide reduced plasma glucose, triglycerides and NEFA concentrations during the SFA diet (by 50%, 25% and 9%, respectively), and the SFA diet increased plasma glucose during the IST (by 36%; all P < .01 vs placebo). The SFA diet-induced impairment of vasodilation on placebo (-9.4% vs baseline; P < .01) was ameliorated by liraglutide (-4.8%; P = .1 vs baseline). In skeletal muscle, liraglutide abolished the SFA-induced increase in thioredoxin-interacting protein (TxNIP) expression (75% decrease; P < .01 vs placebo) and increased 5'AMP-activated protein kinase (AMPK) phosphorylation (50% vs -3%; P = .04 vs placebo). CONCLUSIONS: Liraglutide blunted the SFA-enriched diet-induced peripheral insulin resistance. This effect may be related to improved microvascular function and modulation of TxNIP and AMPK pathways in skeletal muscle.

A human model of dietary saturated fatty acid induced insulin resistance.

BACKGROUND: Increased consumption of high-fat diets is associated with the development of insulin resistance and type 2 diabetes. Current models to study the mechanisms of high-fat diet-induced IR in humans are limited by their long duration or low efficacy. In the present study we developed and characterized an acute dietary model of saturated fatty acid-enriched diet induced insulin resistance. METHODS: High caloric diets enriched with saturated fatty acids (SFA) or carbohydrates (CARB) were evaluated in subjects with normal and impaired glucose tolerance (NGT or IGT). Both diets were compared to a standard eucaloric American Heart Association (AHA) control diet in a series of crossover studies. Whole body insulin resistance was estimated as steady state plasma glucose (SSPG) concentrations during the last 30min of a 3-h insulin suppression test. RESULTS: SSPG was increased after a 24-h SFA diet (by 83±74% vs. control, n=38) in the entire cohort, which was comprised of participants with NGT (92±82%, n=22) or IGT (65±55%, n=16) (all p<0.001). SSPG was also increased after a single SFA breakfast (55±32%, p=0.008, n=7). The increase in SSPG was less pronounced after an overnight fast following a daylong SFA diet (24±31%, p=0.04, n=10), and further attenuated 24h after returning to the control diet (19±35%, p=0.09, n=11). SSPG was not increased after a 24-h CARB diet (26±50%, p=0.11, n=12). CONCLUSIONS: A short-term SFA-enriched diet induced whole body insulin resistance in both NGT and IGT subjects. Insulin resistance persisted overnight after the last SFA meal and was attenuated by one day of a healthy diet. This model offers opportunities for identifying early mechanisms and potential treatments of dietary saturated fat induced insulin resistance.

Posttranslational modifications of apolipoprotein A-II proteoforms in type 2 diabetes.

BACKGROUND: Apolipoprotein A-II (apoA-II) is the second most abundant protein in high-density lipoprotein particles. However, it exists in plasma in multiple forms. The effect of diabetes on apoA-II proteoforms is not known. OBJECTIVE: Our objective was to characterize plasma apoA-II proteoforms in participants with and without type 2 diabetes. METHODS: Using a novel mass spectrometric immunoassay, the relative abundance of apoA-II proteoforms was examined in plasma of 30 participants with type 2 diabetes and 25 participants without diabetes. RESULTS: Six apoA-II proteoforms (monomer, truncated TQ monomer, truncated Q monomer, dimer, truncated Q dimer, and truncated 2Qs dimer) and their oxidized proteoforms were identified. The ratios of oxidized monomer and all oxidized proteoforms to the native apoA-II were significantly greater in the diabetic group (P = .004 and P = .005, respectively) compared with the nondiabetic group. CONCLUSION: The relative abundance of oxidized apoA-II is significantly increased in type 2 diabetes.

The association of plasma cystatin C proteoforms with diabetic chronic kidney disease.

BACKGROUND: Cystatin C (CysC) is an endogenous cysteine protease inhibitor that can be used to assess the progression of kidney function. Recent studies demonstrate that CysC is a more specific indicator of glomerular filtration rate (GFR) than creatinine. CysC in plasma exists in multiple proteoforms. The goal of this study was to clarify the association of native CysC, CysC missing N-terminal Serine (CysC des-S), and CysC without three N-terminal residues (CysC des-SSP) with diabetic chronic kidney disease (CKD). RESULTS: Using mass spectrometric immunoassay, the plasma concentrations of native CysC and the two CysC truncation proteoforms were examined in 111 individuals from three groups: 33 non-diabetic controls, 34 participants with type 2 diabetes (DM) and without CKD and 44 participants with diabetic CKD. Native CysC concentrations were 1.4 fold greater in CKD compared to DM group (p = 0.02) and 1.5 fold greater in CKD compared to the control group (p = 0.001). CysC des-S concentrations were 1.55 fold greater in CKD compared to the DM group (p = 0.002) and 1.9 fold greater in CKD compared to the control group (p = 0.0002). CysC des-SSP concentrations were 1.8 fold greater in CKD compared to the DM group (p = 0.008) and 1.52 fold greater in CKD compared to the control group (p = 0.002). In addition, the concentrations of CysC proteoforms were greater in the setting of albuminuria. The truncated CysC proteoform concentrations were associated with estimated GFR independent of native CysC concentrations. CONCLUSION: Our findings demonstrate a greater amount of CysC proteoforms in diabetic CKD. We therefore suggest assessing the role of cystatin C proteoforms in the progression of CKD.