Type 2 diabetes partitioned polygenic risk scores (pPRS) are related to their physiological impact on insulin secretion and sensitivity. We investigated associations of two pPRS sets obtained from multiancestry cohorts with the relationship between insulin secretion and sensitivity and diabetes incidence in the Diabetes Prevention Program (DPP). We generated 12 and 8 pPRS from soft- and hard-clustering approaches, respectively, in 2,052 DPP participants randomized to intensive lifestyle intervention, metformin, or placebo. Baseline insulin secretion demand and compensation were estimated through the relationship between secretion and sensitivity. Most expected associations of pPRS with insulin secretion and sensitivity were replicated. Some pPRS associated with lower secretion compensation. Global PRS associations with diabetes incidence were stronger than those of any pPRS in both sets. When insulin secretion compensation and demand modified pPRS associations with diabetes incidence, modification occurred only for demand: higher compensation associated with decreased diabetes incidence regardless of pPRS level. A β-cell dysfunction pPRS interacted with DPP treatments in a way that suggested that these treatments may be less effective in those genetically predisposed to diabetes due to insulin deficiency. Regardless of genetic risk as measured by pPRS, inadequate compensatory insulin secretion contributes to progression to diabetes in people with prediabetes.

We investigated whether lowering dietary carbohydrate content and glycemic index (GI) levels altered deep lipidomic profiles and whether these changes were associated with improved diurnal postprandial glucose response (PPGR). In the OmniCarb trial, 59 adults completed 5-week controlled feeding interventions (low carbohydrate/low GI vs. high carbohydrate/high GI) and 12-h meal tests. Comprehensive lipidomic profiling was performed to measure lipid species and lipid class-specific fatty acids (FAs) at the end of each intervention. We found that lowering carbohydrate content and GI levels significantly decreased triacylglycerols (TAGs) and phosphatidylcholines, while increasing lactosylceramides and phosphatidylethanolamines (PEs). Of 731 lipid species analyzed, 521 (71%) were significantly modified, including TAGs (n = 398), PEs (n = 45), and ceramides. Of 199 FAs analyzed across and within lipid classes, 89 showed significant changes (false discovery rate-adjusted P < 0.05), including decreases in saturated FAs (total and TAG FA12:0 and FA14:0) and palmitoleic acid and increases in very-long-chain saturated FAs, when lowering carbohydrate and GI levels. Between-diet changes in six total FAs and 17 lipid class-specific FAs were associated with half-day PPGR changes; greater decreases in joint FA score changes were linked to improved PPGRs. Our study suggests the potential importance of dietary carbohydrate-responsive lipidomic signatures in explaining individual variability in half-day PPGRs and may encourage future intervention studies to target these signatures.

Glucose-dependent insulinotropic polypeptide (GIP[1-42]) increases glucagon levels in the presence of normal-to-low plasma glucose concentrations in individuals with type 1 diabetes (T1D), suggesting its potential use as a safeguard against hypoglycemia. We investigated the dose-dependent effects of exogenous full-length GIP[1-42] and its truncated variant GIP[1-30]NH2 on glucagon concentrations during insulin-induced hypoglycemia in individuals with T1D. In a randomized, double-blind, placebo-controlled, crossover study, 10 men with C-peptide-negative T1D participated in five experimental visits. On each visit, participants received a 135-min intravenous infusion of GIP[1-42] or GIP[1-30]NH2 (both at 4 or 8 pmol/kg/min), or placebo. The infusion period included a 30-min euglycemic period, a 60-min insulin-induced hypoglycemic clamp (target glucose 2.5 mmol/L), and a 45-min recovery phase. During the euglycemic period, glucagon concentrations were higher with all GIP infusions compared with placebo, reaching statistical significance only for GIP[1-30]NH2 (P < 0.05 for both high-dose [8 pmol/kg/min] and low-dose [4 pmol/kg/min]). However, the insulin infusion suppressed glucagon to similarly low levels for all interventions. Both GIP variants increased norepinephrine levels, and high-dose GIP[1-42] slightly reduced the amount of glucose required to recover from hypoglycemia. These findings demonstrate that although GIP acutely increases glucagon concentrations during euglycemia in T1D, insulin infusion overrides this effect, indicating that elevated GIP levels alone cannot effectively restore the glucagon response to insulin-induced hypoglycemia in T1D.

The naturally occurring peptide, liver-expressed antimicrobial peptide 2 (LEAP2), has gained interest as a ghrelin receptor antagonist. We previously reported reduced food intake and plasma glucose-lowering effects of LEAP2 infusion in lean healthy men; however, the effects of this competitive antagonist and inverse agonist of the ghrelin receptor in men with obesity have not been investigated. In the current study, 20 men with obesity were enrolled in a randomized, double-blind, placebo-controlled, crossover study comprising two experimental visits, each involving a ∼5-h intravenous infusion of LEAP2 (infusion rate 40 pmol/kg/min) or placebo during which a liquid mixed meal test and a subsequent ad libitum meal test were performed. The LEAP2 infusion resulted in a fivefold increase in plasma concentrations of LEAP2 compared with placebo. The infusion lowered postprandial plasma glucose levels and reduced ad libitum food intake by ∼12%. We conclude that a continuous intravenous LEAP2 infusion reduces glycemia and food intake in men with obesity, supporting further exploration of LEAP2's therapeutic potential in obesity and related metabolic conditions.

Glucagon-like peptide 1 (GLP-1) receptor agonists improve dyslipidemia and reduce cardiovascular risk in type 2 diabetes (T2D), but the role of endogenous GLP-1 in lipid metabolism remains unclear. We evaluated the effect of dipeptidyl peptidase 4 (DPP-4) inhibition on the response of plasma triglycerides (TGs) to intraduodenal lipid and a mixed meal, and the impact of GLP-1 receptor blockade with exendin(9-39) in T2D. Fifteen participants with T2D, managed by diet and/or metformin, were studied on three occasions in a double-blind, randomized, crossover design. Vildagliptin (50 mg) or placebo was administered orally (t = -60 min), followed by intravenous exendin(9-39) from t = -60 to 150 min on one of the two vildagliptin days or 0.9% saline on two other days. A lipid emulsion was infused intraduodenally (2 kcal/min, t = 0-120 min), followed by a mixed meal (t = 120-150 min). Plasma TG levels, quantified by liquid chromatography-tandem mass spectrometry, increased after lipid and meal, with most individual TGs corresponding to those in the lipid emulsion. Vildagliptin reduced TG(54:4) and TG(54:5) concentrations (each P < 0.01), without affecting total TGs. Blocking endogenous GLP-1 during vildagliptin treatment increased plasma total TGs (P < 0.001), associated with elevations of 10 individual TG species (P < 0.05 each). These outcomes suggest that endogenous GLP-1 contributes to the physiological modulation of postprandial TG appearance in T2D.

There is significant interest in antigen-specific approaches to delaying type 1 diabetes in preclinical stages and supporting tolerance after diagnosis. We conducted a phase I trial of a nonintegrating DNA plasmid constructed to secrete the type 1 diabetes antigen preproinsulin (PPI) and the immune modulatory cytokines transforming growth factor-β1 (TGF-β1), interleukin-10 (IL-10), and IL-2. In this placebo-controlled, double-masked study of 47 adults with stage 3 type 1 diabetes, we showed that the drug is safe and well tolerated, with most reported adverse events (AEs) categorized as grade 1 and with no clinically significant difference in AEs among treatment groups. There were no untoward metabolic or immune effects. We found pharmacodynamic evidence of treatment, as demonstrated by a dose-dependent type 1 interferon (IFN) signature. Plasmid DNA, representing a pharmocokinetic measure, was detected in the two highest dosing groups. We did not find global or antigen-specific immune cell changes following treatment with a DNA plasmid expressing PPI, IL-2, IL-10, and TGF-β1, and we did not detect immune changes driven by IL-2, IL-10, or TGF-β1. Our results support further trials of this novel tolerizing antigen construct.

Abatacept, a cytotoxic T lymphocyte–associated protein 4 immunoglobulin that inhibits T-cell costimulation, was evaluated for 12 months in stage 1 type 1 diabetes (T1D) to delay disease progression. Despite modest preservation of area under the curve C-peptide at 12 months, the primary end point was not met. We adopted the oral minimal model (OMM) to assess β-cell function over 48 months and explored how baseline insulin secretion (ϕtotal) modified treatment response. Using the OMM, ϕtotal was computed from oral glucose tolerance tests conducted at baseline and every 6 months. Participants were stratified into high- and low-secretor groups depending on baseline ϕtotal ≥33rd or <33rd centile, respectively. A sensitivity analysis was performed to validate threshold choice. Among 203 participants (abatacept n = 96; 107 placebo n = 107), 39% receiving abatacept and 47% receiving placebo experienced progression to stage 2 or 3 within 96 months. High secretors receiving abatacept gained 15.8 progression-free months (95% CI 4.85, 26.68; P = 0.005) and had a 54% lower hazard of progression versus those receiving placebo (hazard ratio [HR] 0.46; 95% CI 0.25, 0.84; P = 0.012). Treatment effect differed significantly by secretor status (interaction HR 2.92; 95% CI 1.23, 6.96; P = 0.015). A subgroup of responders to 12 months of abatacept was identified by ϕtotal, providing the first evidence that an immune intervention in stage 1 T1D may delay disease progression.

Despite stimulating glucagon secretion, the mechanisms by which protein ingestion lowers glucose excursions remain unclear. We investigated this using the triple stable isotope glucose tracer technique to measure postprandial glucose fluxes. Eleven healthy adults completed three trials, ingesting 25 g glucose (25G; 100 kcal), 50 g glucose (50G; 200 kcal), or 25 g glucose plus 25 g whey protein (25WG; 200 kcal). Glucose excursions were lowest for 25WG. Glucagon increased approximately threefold with 25WG but was suppressed with 25G and 50G. Insulin and glucose-dependent insulinotropic polypeptide (GIP) were higher for 25WG versus 25G, whereas glucagon-like peptide 1 (GLP-1) was similar. Compared with 50G, 25WG produced a greater GIP but similar GLP-1 response, with a trend toward higher early-phase insulin. Endogenous glucose production (EGP) was less suppressed with 25WG (∼50%) versus 25G (∼70%) or 50G (∼80%). Compared with 25G, 25WG did not enhance glucose disposal (Rd) but reduced early-phase (30-60 min) glucose absorption. These findings confirm that protein-glucose coingestion robustly stimulates glucagon while enhancing GIP and insulin, leading to lower postprandial glucose excursions. Despite greater insulin secretion, the net glycemic benefit seems to stem from reduced early glucose absorption rather than increased Rd. This provides novel insights into the mechanisms by which protein improves postprandial glucose handling despite interfering with EGP suppression.

Dorzagliatin is a dual-acting allosteric activator of glucokinase (GCK). Dorzagliatin improved second-phase insulin secretion in individuals with type 2 diabetes and heterozygous carriers of GCK mutations. We investigated the effects of dorzagliatin on pancreatic insulin, glucagon, and glucagon-like-peptide 1 (GLP-1) secretion in individuals with impaired glucose tolerance (IGT) and normal glucose tolerance (NGT). In a double-blind, randomized, crossover, single-dose study, 9 participants with IGT and 10 with NGT underwent 2-h 12 mmol/L hyperglycemic clamp following a single dose of dorzagliatin 50 mg or matched placebo. Plasma insulin, C-peptide, glucagon, and total GLP-1 levels were measured at regular intervals. There were no differences in first-phase insulin after the dorzagliatin dose in either group. Dorzagliatin significantly increased second-phase insulin secretion rate and β-cell glucose sensitivity by 1.3-fold compared with placebo in IGT but remained similar in NGT. Dorzagliatin increased basal plasma insulin in the NGT group only. Glucagon (area under the curve0-120 min = 161 ± 58 vs. 234 ± 70 pmol*min/L [mean ± SD]; P = 0.01) was suppressed after dorzagliatin in the NGT group but not the IGT group. Plasma glucagon was positively correlated with total GLP-1 levels. Dorzagliatin did not affect insulin sensitivity in either group. Dorzagliatin has different actions on β- and α-cells depending on glucose tolerance, increasing second-phase insulin secretion in IGT while enhancing glucose-suppression of glucagon secretion in NGT.

We evaluated whether a binary metabolic end point for change (Δ) from baseline to 1-year postrandomization could be useful in type 1 diabetes (T1D) prevention trials. Using 2-h oral glucose tolerance testing data from the stage 1 participants in the recent abatacept prevention trial and similar participants in the observational TrialNet Pathway to Prevention (PTP) study, we assessed Δmetabolic measures, plotted glucose and C-peptide response curves, and categorized vectors for Δ from baseline to 1 year as metabolic treatment failure versus success. Analyses were validated using the teplizumab prevention study. PTP participants with Δglucose >0 and ΔC-peptide <0 from baseline to 1 year were at substantially higher risk for stage 3 T1D than those with Δglucose <0 and ΔC-peptide >0 (P < 0.0001). Based on this, we compared placebo versus treatment groups in both trials for failure (Δglucose >0 with ΔC-peptide <0) versus success (Δglucose <0 with ΔC-peptide >0) after 1 year. Using this end point, a favorable metabolic impact of abatacept was found after 12 months of treatment. An analytic approach using a binary metabolic end point of failure versus success at a fixed time interval appears to detect treatment effects at least as well as standard primary end points with shorter follow-up.

Sodium-glucose cotransporter 2 inhibitors (SGLT2i) cause an increase in hepatic glucose production (HGP). We previously showed that SGLT2i cause a rapid (within 4 h) increase in the total-body norepinephrine (NE) turnover rate, which could explain the increase in HGP. Because the increase in HGP caused by SGLT2i is long-lasting, we examined the long-term effect of SGLT2i on the NE turnover rate. Empagliflozin caused a decrease in total-body NE turnover at 1 day and at 12 weeks after starting therapy, despite an increase in glucose production, and the magnitude of decrease in NE turnover inversely correlated with the increase in HGP caused by empagliflozin.

This post hoc analysis assessed sustainability of lowered glycated hemoglobin (HbA1c) and weight with tirzepatide in people with type 2 diabetes and increased cardiovascular risk. Participants achieving HbA1c ≤48 mmol/mol (6.5%) or weight loss ≥10% at 52 weeks were evaluated for sustained glycemic or weight control and predictors of initial and sustained efficacy. For tirzepatide-treated participants achieving HbA1c ≤48 mmol/mol (6.5%) at 52 weeks, 75-84% sustained this until study end (median 81 weeks). Factors predicting achievement were higher tirzepatide dose, shorter diabetes duration, and lower HbA1c, higher HOMA of β-cell function (HOMA-B), metformin alone, and absence of albuminuria at baseline. Factors predicting sustained glycemic control were greater weight loss, smaller fasting glucose decrease, no sulfonylurea, and higher HOMA-B at 52 weeks. For participants achieving ≥10% weight loss at 52 weeks, 79-82% maintained weight loss. Factors predicting achievement were higher tirzepatide dose, female sex, no cardiovascular disease history, and lower baseline HbA1c, estimated glomerular filtration rate, and triglycerides. Greater decrease in LDL-cholesterol to 52 weeks predicted maintained weight loss. Greater weight loss and better β-cell function achieved with tirzepatide were the main predictors for sustained glycemic control in this post hoc analysis; no clinically meaningful predictor was identified for sustained weight control.

The diabetic heart has reduced ketone utilization due to impaired ketolytic enzyme activity. In a randomized controlled crossover trial, we investigated whether the cardiac response to 3-hydroxybutyrate infusion is impaired in type 1 diabetes. The response on cardiac output was blunted by 80% in type 1 diabetes, with no improvement in systolic function and left ventricular work efficiency was reduced. These findings suggest impaired cardiac ketone metabolism may have clinical significance and could contribute to diabetic cardiomyopathy.

Gastrointestinal hormones are essential for nutrient handling and regulation of glucose metabolism and may affect postprandial blood redistribution. In a randomized cross-over design in 10 healthy men, the involvement of glucose-dependent insulinotropic polypeptide (GIP) in splanchnic blood flow regulation was investigated using an infusion of GIP receptor antagonist (GIPR-An) GIP(3-30)NH2 during ingestion of oral glucose (75 g). In five separate sessions, we investigated GIP(1-42), GIPR-An with and without oral glucose, oral glucose alone, and a control saline infusion. Blood flow was assessed by phase contrast MRI, hepatic oxygen consumption by T2*, and plasma glucose, insulin, C-peptide, glucagon, GIP, GIPR-An, glucagon-like peptide 2, and bone metabolism markers by frequent blood sampling during all sessions. We found GIP(1-42) to stimulate blood flow in the superior mesenteric artery by ∼10% in the fasting state. Oral glucose alone increased mean blood flow in the superior mesenteric artery by ∼70% and portal vein by ∼40% of baseline. During oral glucose ingestion with concurrent infusion of GIPR-An, blood flow in the superior mesenteric artery was ∼22% lower. The hormone infusions did not affect blood flow in the hepatic artery and the celiac artery. Infusion of GIPR-An during oral glucose ingestion resulted in lower insulin secretion and higher levels of carboxy-terminal collagen crosslinks (bone resorption biomarker) compared with saline infusion, whereas glucagon levels were unaffected by both the injection of GIP and the GIPR-An infusions. We conclude that endogenous GIP increases splanchnic blood flow and contributes to postprandial intestinal hyperemia in healthy men.

The impact of atmospheric pressure changes on glucose metabolism encountered in aviation on people with type 1 diabetes is controversial. A dual-isotope study was performed in a hypobaric chamber to simulate pressure changes experienced on commercial flights. The fasting and postprandial glucose kinetics of individuals with type 1 diabetes were evaluated across simulated in-flight cabin pressures (550 mmHg; experimental arm) and ground level (750 mmHg; control arm). The impact of ambient pressure on glucose disposal (Rd), endogenous glucose production (EGP), meal glucose appearance (Ra), and insulin concentrations were evaluated. Six male participants, aged 20-61 years, with a median BMI of 26.6 kg/m2, were studied. Baseline glucose Rd, EGP, and meal Ra values were not affected by ambient pressure changes. Postprandial glucose Rd was higher in hypobaric conditions than ground, the percent change in postprandial glucose concentration was lower, but postprandial EGP and meal Ra were not affected. Insulin concentration between 120 and 180 min was higher in the hypobaric simulation. The observed increase in glucose Rd for individuals with type 1 diabetes who were using insulin pumps may be related to the hypoxia and pressure changes experienced during flight. Because glucose profiles were unaffected, there is no evidence that insulin pump therapy is a risk factor in flight.

Activation of GPR119 receptors, expressed on enteroendocrine and pancreatic islet cells, augments glucagon counterregulatory responses to hypoglycemia in preclinical models. We hypothesized that MBX-2982, a GPR119 agonist, would augment counterregulatory responses to experimental hypoglycemia in participants with type 1 diabetes (T1D). To assess this, we designed a phase 2a, double-masked, crossover trial in 18 participants (age 20-60 years) with T1D. Participants were randomized to treatment with 600 mg MBX-2982 or placebo daily for 14 days, with a 2-week washout between treatments. Counterregulatory responses to hypoglycemia during a hyperinsulinemic euglycemic-hypoglycemic clamp and hormonal responses during a mixed-meal test (MMT) were measured. The maximum glucagon response, glucagon area under the curve (AUC), and incremental AUC were not significantly different during MBX-2982 versus placebo treatment. MBX-2982 did not alter epinephrine, norepinephrine, pancreatic polypeptide, free fatty acid, or endogenous glucose production responses to hypoglycemia compared with placebo. However, glucagon-like peptide 1 (GLP-1) response during the MMT was 17% higher with MBX-2982 compared with placebo treatment. In conclusion, GPR119 activation with MBX-2982 did not improve counterregulatory responses to hypoglycemia in people with T1D. Increases in GLP-1 during the MMT are consistent with GPR119 target engagement and the expected pharmacodynamic response from L cells.

Postprandial hypotension (PPH) occurs frequently in type 2 diabetes. Metformin has cardiovascular effects independent of its glucose-lowering capacity, which may modulate the risk of PPH. We investigated the effects of metformin on postprandial blood pressure, including PPH events, heart rate, glucose, insulin, glucagon-like peptide 1 (GLP-1), and gastric emptying, in individuals with type 2 diabetes. Metformin attenuated postprandial decrease in blood pressure and reduced PPH events, in association with augmentation of plasma GLP-1, slowed gastric emptying, and increased heart rate, in type 2 diabetes. These findings establish novel cardiovascular effects of metformin that may mitigate the risk of PPH in type 2 diabetes.

Our objective was to test a single dose of the phosphatidylinositol 3-kinase (PI3K) inhibitor alpelisib as a tool for acute modeling of insulin resistance in healthy volunteers. This single-center double-blind phase 1 clinical trial randomly assigned healthy adults to a single oral dose of 300 mg alpelisib (n = 5) or placebo (n = 6) at bedtime, followed by measurement of glucose, insulin, and C-peptide levels after an overnight fast and during a 3-h 75-g oral glucose tolerance test (OGTT). Fasting plasma glucose trended higher with alpelisib (mean ± SD 93 ± 11 mg/dL) versus placebo (84 ± 5 mg/dL); mean fasting serum insulin increased nearly fivefold (23 ± 12 vs. 5 ± 3 μU/mL, respectively), and HOMA of insulin resistance (IR) scores were 5.4 ± 3.1 for alpelisib and 1.1 ± 0.6 for placebo. During OGTT, incremental area under the curve (AUC) for insulin was more than fourfold greater with alpelisib (22 ± 15 mU/mL × min) than with placebo (5 ± 2 mU/mL × min); glucose AUC trended higher with alpelisib. Single-dose alpelisib was well tolerated and produced metabolic alterations consistent with acute induction of IR, validating its use for mechanistic study of insulin action in humans.

A ketogenic diet (KD) can induce weight loss and improve glycemic regulation, potentially reducing the risk of type 2 diabetes development. To elucidate the underlying mechanisms behind these beneficial effects of a KD, we investigated the impact of a KD on organ-specific insulin sensitivity (IS) in skeletal muscle, liver, and adipose tissue. We hypothesized that a KD would increase IS in skeletal muscle. The study included 11 individuals with obesity who underwent a randomized, crossover trial with two 3-week interventions: 1) a KD and 2) a standard diet. Skeletal muscle IS was quantified as the increase in glucose disposal during a hyperinsulinemic-euglycemic clamp (HEC). Hepatic IS and adipose tissue IS were quantified as the relative suppression of endogenous glucose production (EGP) and the relative suppression of palmitate flux during the HEC. The KD led to a 2.2-kg weight loss and increased insulin-stimulated glucose disposal, whereas the relative suppression of EGP during the HEC was similar. In addition, the KD decreased insulin-mediated suppression of lipolysis. In conclusion, a KD increased skeletal muscle IS in individuals with obesity.

Partitioned polygenic scores (pPS) have been developed to capture pathophysiologic processes underlying type 2 diabetes (T2D). We investigated the association of T2D pPS with diabetes-related traits and T2D incidence in the Diabetes Prevention Program. We generated five T2D pPS (β-cell, proinsulin, liver/lipid, obesity, lipodystrophy) in 2,647 participants randomized to intensive lifestyle, metformin, or placebo arms. Associations were tested with general linear models and Cox regression with adjustment for age, sex, and principal components. Sensitivity analyses included adjustment for BMI. Higher β-cell pPS was associated with lower insulinogenic index and corrected insulin response at 1-year follow-up with adjustment for baseline measures (effect per pPS SD -0.04, P = 9.6 × 10-7, and -8.45 μU/mg, P = 5.6 × 10-6, respectively) and with increased diabetes incidence with adjustment for BMI at nominal significance (hazard ratio 1.10 per SD, P = 0.035). The liver/lipid pPS was associated with reduced 1-year baseline-adjusted triglyceride levels (effect per SD -4.37, P = 0.001). There was no significant interaction between T2D pPS and randomized groups. The remaining pPS were associated with baseline measures only. We conclude that despite interventions for diabetes prevention, participants with a high genetic burden of the β-cell cluster pPS had worsening in measures of β-cell function.