Lipid-induced glucose intolerance is driven by impaired glucose kinetics and insulin metabolism in healthy individuals

AIMS

Hypertriglyceridemia is associated with an increased risk of type 2 diabetes. We aimed to comprehensively examine the effects of hypertriglyceridemia on major glucose homeostatic mechanisms involved in diabetes progression.

METHODS

In this randomized, cross-over, single-blinded study, two dual-labeled, 3-hour oral glucose tolerance tests were performed during 5-hour intravenous infusions of either 20 % Intralipid or saline in 12 healthy subjects (age 27.9 ± 2.6 years, 11 men, BMI 22.6 ± 1.4 kg/m²) to evaluate lipid-induced changes in insulin metabolism and glucose kinetics. Insulin sensitivity, β cell secretory function, and insulin clearance were assessed by modeling glucose, insulin and C-peptide data. Intestinal glucose absorption, endogenous glucose production, and glucose clearance were assessed from glucose tracers. The effect of triglycerides on β-cell secretory function was examined in perifusion experiments in murine pseudoislets and human pancreatic islets.

RESULTS

Mild acute hypertriglyceridemia impaired oral glucose tolerance (mean glucose: +0.9 [0.3, 1.5] mmol/L, p = 0.008) and whole-body insulin sensitivity (Matsuda index: -1.67 [-0.50, -2.84], p = 0.009). Post-glucose hyperinsulinemia (mean insulin: +99 [17, 182] pmol/L, p = 0.009) resulted from reduced insulin clearance (-0.16 [-0.32, -0.01] L min^-1 m^-2, p = 0.04) and enhanced hyperglycemia-induced total insulin secretion (+11.9 [1.1, 22.8] nmol/m², p = 0.02), which occurred despite a decline in model-derived β cell glucose sensitivity (-41 [-74, -7] pmol min^-1 m^-2 mmol^-1 L, p = 0.04). The analysis of tracer-derived glucose metabolic fluxes during lipid infusion revealed lower glucose clearance (-96 [-152, -41] mL/kg_FFM, p = 0.005), increased 2-hour oral glucose absorption (+380 [42, 718] μmol/kg_FFM, p = 0.04) and suppressed endogenous glucose production (-448 [-573, -123] μmol/kg_FFM, p = 0.005). High-physiologic triglyceride levels increased acute basal insulin secretion in murine pseudoislets (+11 [3, 19] pg/aliquot, p = 0.02) and human pancreatic islets (+286 [59, 512] pg/islet, p = 0.02).

CONCLUSION

Our findings support a critical role for hypertriglyceridemia in the pathogenesis of type 2 diabetes in otherwise healthy individuals and dissect the glucose homeostatic mechanisms involved, encompassing insulin sensitivity, β cell function and oral glucose absorption.

Reversibility of brain glucose kinetics in type 2 diabetes mellitus

AIMS/HYPOTHESIS

We have previously shown that individuals with uncontrolled type 2 diabetes have a blunted rise in brain glucose levels measured by ¹H magnetic resonance spectroscopy. Here, we investigate whether reductions in HbA_1c normalise intracerebral glucose levels.

METHODS

Eight individuals (two men, six women) with poorly controlled type 2 diabetes and mean ± SD age 44.8 ± 8.3 years, BMI 31.4 ± 6.1 kg/m² and HbA_1c 84.1 ± 16.2 mmol/mol (9.8 ± 1.4%) underwent ¹H MRS scanning at 4 Tesla during a hyperglycaemic clamp (~12.21 mmol/l) to measure changes in cerebral glucose at baseline and after a 12 week intervention that improved glycaemic control through the use of continuous glucose monitoring, diabetes regimen intensification and frequent visits to an endocrinologist and nutritionist.

RESULTS

Following the intervention, mean ± SD HbA_1c decreased by 24.3 ± 15.3 mmol/mol (2.1 ± 1.5%) (p=0.006), with minimal weight changes (p=0.242). Using a linear mixed-effects regression model to compare glucose time courses during the clamp pre and post intervention, the pre-intervention brain glucose level during the hyperglycaemic clamp was significantly lower than the post-intervention brain glucose (p<0.001) despite plasma glucose levels during the hyperglycaemic clamp being similar (p=0.266). Furthermore, the increases in brain glucose were correlated with the magnitude of improvement in HbA_1c (r = 0.71, p=0.048).

CONCLUSION/INTERPRETATION

These findings highlight the potential reversibility of cerebral glucose transport capacity and metabolism that can occur in individuals with type 2 diabetes following improvement of glycaemic control. Trial registration ClinicalTrials.gov NCT03469492.

The effect of glucose control in liver surgery on glucose kinetics and insulin resistance

BACKGROUND & AIMS

Clinical outcome is negatively correlated to postoperative insulin resistance and hyperglycemia. The magnitude of insulin resistance can be modulated by glucose control, preoperative nutrition, adequate pain management and minimal invasive surgery. Effects of glucose control on perioperative glucose kinetics in liver surgery is less studied.

METHODS

18 patients scheduled for open hepatectomy were studied per protocol in this prospective, randomized study. In the treatment group (n = 9), insulin was administered intravenously to keep arterial blood glucose between 6 and 8 mmol/l during surgery. The control group (n = 9) received insulin if blood glucose >11.5 mmol/l. Insulin sensitivity was measured by an insulin clamp on the day before surgery and immediately postoperatively. Glucose kinetics were assessed during the clamp and surgery.

RESULTS

Mean intraoperative glucose was 7.0 mM (SD 0.7) vs 9.1 mM (SD 1.9) in the insulin and control group respectively (p < 0.001; ANOVA). Insulin sensitivity decreased in both groups but significantly (p = 0.03, ANOVA) more in the control group (M value: 4.6 (4.4-6.8) to 2.1 (1.2-2.6) and 4.6 (4.1-5.0) to 0.6 (0.1-1.8) mg/kg/min in the treatment and control group respectively). Endogenous glucose production (EGP) increased and glucose disposal (WGD) decreased significantly between the pre- and post-operative clamps in both groups, with no significant difference between the groups. Intraoperative kinetics demonstrated that glucose control decreased EGP (p = 0.02) while WGD remained unchanged (p = 0.67).

CONCLUSION

Glucose control reduces postoperative insulin resistance in liver surgery. EGP increases and WGD is diminished immediately postoperatively. Insulin seems to modulate both reactions, but mostly the WGD is affected. Intraoperative EGP decreased while WGD remained unaltered.

REGISTRATION NUMBER OF CLINICAL TRIAL

ANZCTR 12614000278639.

Metformin increases endogenous glucose production in non-diabetic individuals and individuals with recent-onset type 2 diabetes

AIMS/HYPOTHESIS

Metformin is the endorsed first-line glucose-lowering drug for treating patients with type 2 diabetes but despite more than 50 years of use, no consensus has been reached on its mechanisms of action. In this study, we investigated the glucose-lowering effects of metformin in individuals with type 2 diabetes and non-diabetic individuals.

METHODS

We performed a randomised, placebo-controlled trial in 24 individuals with recent-onset type 2 diabetes (diabetes duration 50 [48] months) who had good glycaemic control (HbA_1c 48 mmol/mmol [6.5%]). The studies were conducted at Aarhus University Hospital between 2013 and 2016. Participants were randomised to receive either metformin (2000 mg/day, n = 12, MET group) or placebo (n = 12, PLA group) for 90 days, using block randomisation set up by an unblinded pharmacist. Two participants withdrew from the study prior to completion and were replaced with two new participants receiving the same treatment. In addition, we recruited a group of non-diabetic individuals with similar age and BMI (n = 12, CONT group), who were all treated with 2000 mg metformin daily. Before and after treatment all individuals underwent studies of whole-body glucose metabolism by non-steady-state [3-³H]glucose kinetics, hyperinsulinaemic-euglycaemic clamping, indirect calorimetry, metabolomics, dual x-ray absorptiometry and muscle biopsies. The primary study endpoint was the effect of metformin treatment on lipid kinetics as well as glucose rate of disappearance (R_d) and endogenous glucose production (EGP).

RESULTS

One participant from the CONT group withdrew due to intolerable gastrointestinal side-effects and was excluded from analysis. As expected, metformin treatment lowered fasting plasma glucose (FPG) in the MET group (~1.5 mmol/l, p < 0.01), whereas no effect was observed in the PLA and CONT groups. Body weight and composition did not change in any of the groups. In both of the metformin-treated groups (MET and CONT), basal glucose R_d, EGP and glucagon levels increased by ~30% (p < 0.05) whereas this was not the case in the PLA group.

CONCLUSIONS/INTERPRETATION

Ninety days of metformin treatment resulted in similar increases in EGP and glucose R_d in individuals with recent-onset type 2 diabetes and in non-diabetic control individuals. These results challenge the existing paradigm that metformin primarily acts in the liver by inhibiting EGP, at least in individuals with type 2 diabetes of short duration and who have discretely affected glycaemic status. Whether metformin increases basal glucose R_d by facilitating glucose uptake in other tissues such as the intestines remains to be further clarified.

TRIAL REGISTRATION

ClinicalTrials.gov NCT01729156 FUNDING: This study was supported by grants from The Danish Council for Independent Research | Medical Sciences, Aase Danielsen Fund, the Novo Nordisk Foundation, the Danish Diabetes Association and the Danish Diabetes Academy supported by the Novo Nordisk Foundation.

Effect of alcohol ingestion on plasma glucose kinetics after Roux-en-Y gastric bypass surgery

BACKGROUND

Roux-en-Y gastric bypass surgery (RYGB) increases the rate of alcohol absorption so that peak blood alcohol concentration is 2-fold higher after surgery compared with concentrations reached after consuming the same amount presurgery. Because high doses of alcohol can lead to hypoglycemia, patients may be at increased risk of developing hypoglycemia after alcohol ingestion.

OBJECTIVES

We conducted 2 studies to test the hypothesis that the consumption of approximately 2 standard drinks of alcohol would decrease glycemia more after RYGB than before surgery.

SETTING

Single-center prospective randomized trial.

METHODS

We evaluated plasma glucose concentrations and glucose kinetics (assessed by infusing a stable isotopically labelled glucose tracer) after ingestion of a nonalcoholic drink (placebo) or an alcoholic drink in the following groups: (1) 5 women before RYGB (body mass index = 43 ± 5 kg/m²) and 10 ± 2 months after RYGB (body mass index = 31 ± 7 kg/m²; study 1), and (2) 8 women who had undergone RYGB surgery 2.2 ± 1.2 years earlier (body mass index = 30 ± 5 kg/m²; study 2) RESULTS: Compared with the placebo drink, alcohol ingestion decreased plasma glucose both before and after surgery, but the reduction was greater before (glucose nadir placebo = -.4 ± 1.0 mg/dL versus alcohol = -9.6 ± 1.5 mg/dL) than after (glucose nadir placebo = -1.0 ± 1.6 mg/dL versus alcohol = -5.5 ± 2.6 mg/dL; P < .001) surgery. This difference was primarily due to an alcohol-induced early increase followed by a subsequent decrease in the rate of glucose appearance into systemic circulation.

CONCLUSION

RYGB does not increase the risk of hypoglycemia after consumption of a moderate dose of alcohol.

Effect of feeding garlic leaves on rumen fermentation, methane emission, plasma glucose kinetics, and nitrogen utilization in sheep

Background

Garlic and its constituents are reported to have been effective in reducing methane emission and also influence glucose metabolism in body; however, studies in ruminants using garlic leaves are scarce. Garlic leaves contain similar compounds as garlic bulbs, but are discarded in field after garlic bulb harvest. We speculate that feeding garlic leaves might show similar effect as garlic constituents in sheep and could be potential animal feed supplement. Thus, we examined the effect of freeze dried garlic leaves (FDGL) on rumen fermentation, methane emission, plasma glucose kinetics and nitrogen utilization in sheep.

Methods

Six sheep were fed Control diet (mixed hay and concentrate (60:40)) or FDGL diet (Control diet supplemented with FDGL at 2.5 g/kg BW^0.75 of sheep) using a crossover design. Methane gas emission was measured using open-circuit respiratory chamber. Plasma glucose turnover rate was measured using isotope dilution technique of [U-¹³C]glucose. Rumen fluid, feces and urine were collected to measure rumen fermentation characteristics and nitrogen utilization.

Result

No significant difference in rumen fermentation parameters was noticed except for rumen ammonia tended to be higher (0.05 < P < 0.1) in FDGL diet. Methane emission per kg dry matter ingested and methane emission per kg dry matter digested were lower (P < 0.05) in FDGL diet. Plasma glucose concentration was similar between diets and plasma glucose turnover rate tended to be higher in FDGL diet (0.05 < P < 0.1). Nitrogen retention was higher (P < 0.05) and microbial nitrogen supply tended to be higher (0.05 < P < 0.1) in FDGL diet.

Conclusion

FDGL diet did not impair rumen fermentation, improved nitrogen retention; while absence of significant results in reduction of methane emission, glucose turnover rate and microbial nitrogen supply, further studies at higher dose would be necessary to conclude the merit of FDGL as supplement in ruminant feedstuff.

Direct analysis of [6,6-(2)H2]glucose and [U-(13)C6]glucose dry blood spot enrichments by LC-MS/MS

A liquid chromatography tandem mass spectrometry (LC-MS/MS) using multiple reaction monitoring (MRM) in a triple-quadrupole scan mode was developed and comprehensively validated for the determination of [6,6-(2)H2]glucose and [U-(13)C6]glucose enrichments from dried blood spots (DBS) without prior derivatization. The method is demonstrated with dried blood spots obtained from rats administered with a primed-constant infusion of [U-(13)C6]glucose and an oral glucose load enriched with [6,6-(2)H2]glucose. The sensitivity is sufficient for analysis of the equivalent to <5μL of blood and the overall method was accurate and precise for the determination of DBS isotopic enrichments.

Difference in postprandial GLP-1 response despite similar glucose kinetics after consumption of wheat breads with different particle size in healthy men

Purpose

Underlying mechanisms of the beneficial health effects of low glycemic index starchy foods are not fully elucidated yet. We varied the wheat particle size to obtain fiber-rich breads with a high and low glycemic response and investigated the differences in postprandial glucose kinetics and metabolic response after their consumption.

Methods

Ten healthy male volunteers participated in a randomized, crossover study, consuming ¹³C-enriched breads with different structures; a control bread (CB) made from wheat flour combined with wheat bran, and a kernel bread (KB) where 85 % of flour was substituted with broken wheat kernels. The structure of the breads was characterized extensively. The use of stable isotopes enabled calculation of glucose kinetics: rate of appearance of exogenous glucose, endogenous glucose production, and glucose clearance rate. Additionally, postprandial plasma concentrations of glucose, insulin, glucagon, incretins, cholecystokinin, and bile acids were analyzed.

Results

Despite the attempt to obtain a bread with a low glycemic response by replacing flour by broken kernels, the glycemic response and glucose kinetics were quite similar after consumption of CB and KB. Interestingly, the glucagon-like peptide-1 (GLP-1) response was much lower after KB compared to CB (iAUC, P < 0.005). A clear postprandial increase in plasma conjugated bile acids was observed after both meals.

Conclusions

Substitution of 85 % wheat flour by broken kernels in bread did not result in a difference in glucose response and kinetics, but in a pronounced difference in GLP-1 response. Thus, changing the processing conditions of wheat for baking bread can influence the metabolic response beyond glycemia and may therefore influence health.

Electronic supplementary material

The online version of this article (doi:10.1007/s00394-016-1156-6) contains supplementary material, which is available to authorized users.

The immediate effects of a single bout of aerobic exercise on oral glucose tolerance across the glucose tolerance continuum

We investigated glucose tolerance and postprandial glucose fluxes immediately after a single bout of aerobic exercise in subjects representing the entire glucose tolerance continuum. Twenty‐four men with normal glucose tolerance (NGT), impaired glucose tolerance (IGT), or type 2 diabetes (T2D; age: 56 ± 1 years; body mass index: 27.8 ± 0.7 kg/m², P > 0.05) underwent a 180‐min oral glucose tolerance test (OGTT) combined with constant intravenous infusion of [6,6‐²H₂]glucose and ingestion of [U‐¹³C]glucose, following 1 h of exercise (50% of peak aerobic power) or rest. In both trials, plasma glucose concentrations and kinetics, insulin, C‐peptide, and glucagon were measured. Rates (mg kg⁻¹ min⁻¹) of glucose appearance from endogenous (R_aEndo) and exogenous (oral glucose; R_aOGTT) sources, and glucose disappearance (R_d) were determined. We found that exercise increased R_aEndo, R_aOGTT, and R_d (all P < 0.0001) in all groups with a tendency for a greater (~20%) peak R_aOGTT value in NGT subjects when compared to IGT and T2D subjects. Accordingly, following exercise, the plasma glucose concentration during the OGTT was increased in NGT subjects (P < 0.05), while unchanged in subjects with IGT and T2D. In conclusion, while a single bout of moderate‐intensity exercise increased the postprandial glucose response in NGT subjects, glucose tolerance following exercise was preserved in the two hyperglycemic groups. Thus, postprandial plasma glucose responses immediately following exercise are dependent on the underlying degree of glycemic control.

This study shows that following an exercise bout, plasma glucose concentrations during an oral glucose tolerance test are increased in subjects with normal glucose tolerance, but unchanged in subjects with impaired glucose tolerance or type 2 diabetes. While rates of glucose disappearance and rates of glucose appearance from endogenous sources and from orally ingested glucose were all increased following exercise, there was a 20% greater peak value for the rate of orally ingested glucose appearance in normal glucose tolerant subjects, when compared to IGT and T2D subjects. In summary, postprandial plasma glucose responses immediately following exercise are dependent on the underlying level of glycemic control.