Effect of sitagliptin therapy on triglyceride-rich lipoprotein kinetics in patients with type 2 diabetes

Clinical Consequences of Delayed Gastric Emptying With GLP-1 Receptor Agonists and Tirzepatide

CONTEXT

Glucagon-like peptide-1 (GLP-1) receptor agonists (RAs) are established therapeutics for type 2 diabetes and obesity. Among other mechanisms, they slow gastric emptying and motility of the small intestine. This helps to limit postprandial glycemic excursions and reduce chylomicron formation and triglyceride absorption. Conversely, motility effects may have detrimental consequences, eg, retained gastric contents at endoscopy or general anesthesia, potentially complicated by pulmonary aspiration or bowel obstruction.

DATA ACQUISITION

We searched the PubMed database for studies involving GLP-1RA therapy and adverse gastrointestinal/biliary events.

DATA SYNTHESIS

Retained gastric contents at the time of upper gastrointestinal endoscopy are found more frequently with GLP-1 RAs but rarely are associated with pulmonary aspiration. Well-justified recommendations for the periprocedural management of GLP-1RAs (eg, whether to withhold these medications and for how long) are compromised by limited evidence. Important aspects to be considered are (1) their long half-lives, (2) the capacity of GLP-1 receptor agonism to slow gastric emptying even at physiological GLP-1 concentrations, (c) tachyphylaxis observed with prolonged treatment, and (d) the limited effect on gastric emptying in individuals with slow gastric emptying before initiating treatment. Little information is available on the influence of diabetes mellitus itself (ie, in the absence of GLP-1 RA treatment) on retained gastric contents and pulmonary aspiration.

CONCLUSION

Prolonged fasting periods regarding solid meal components, point-of-care ultrasound examination for retained gastric content, and the use of prokinetic medications like erythromycin may prove helpful and represent an important area needing further study to increase patient safety for those treated with GLP-1 RAs.

Physiology and Pharmacology of Effects of GLP-1-based Therapies on Gastric, Biliary and Intestinal Motility

Glucagon-like peptide-1 (GLP-1) receptor agonists and the dual GLP-1- and glucose-dependent insulinotropic polypeptide receptor co-agonist tirzepatide (referred to here collectively as "GLP-1-based therapy") are incretin-based therapies being used increasingly in the management of both type 2 diabetes and obesity. They are now recognized to have beneficial effects beyond improved glycemic control and weight loss, including cardiovascular and renal protection. GLP-1-based therapy also slows gastric emptying, which has benefits (lowering postprandial glucose), but also potential risks (eg, hypoglycemia in individuals on insulin or sulphonylurea therapy). Their effects on the gallbladder may also be beneficial, contributing to reducing postprandial triglycerides, but they also potentially increase the risk of biliary disease. In this review, we summarize the effects of GLP-1 and incretin-based therapeutics on gastric, biliary and small intestinal function. An improved understanding of these effects will optimize the use of these drugs.

Substitution of dietary monounsaturated fatty acids from olive oil for saturated fatty acids from lard increases low-density lipoprotein apolipoprotein B-100 fractional catabolic rate in subjects with dyslipidemia associated with insulin resistance: a randomized controlled trial

BACKGROUND

The substitution of monounsaturated acids (MUFAs) for saturated fatty acids (SFAs) is recommended for cardiovascular disease prevention but its impact on lipoprotein metabolism in subjects with dyslipidemia associated with insulin resistance (IR) remains largely unknown.

OBJECTIVES

This study aimed to evaluate the impact of substituting MUFAs for SFAs on the in vivo kinetics of apolipoprotein (apo)B-containing lipoproteins and on the plasma lipidomic profile in adults with IR-induced dyslipidemia.

METHODS

Males and females with dyslipidemia associated with IR (n = 18) were recruited for this crossover double-blind randomized controlled trial. Subjects consumed, in random order, a diet rich in SFAs (SFAs: 13.4%E; MUFAs: 14.4%E) and a diet rich in MUFAs (SFAs: 7.1%E; MUFAs: 20.7%E) in fully controlled feeding conditions for periods of 4 wk each, separated by a 4-wk washout. At the end of each diet, fasting plasma samples were taken together with measurements of the in vivo kinetics of apoB-containing lipoproteins.

RESULTS

Substituting MUFAs for SFAs had no impact on triglyceride-rich lipoprotein apoB-48 fractional catabolic rate (FCR) (Δ = -8.9%, P = 0.4) and production rate (Δ = 0.0%, P = 0.9), although it decreased very low-density lipoprotein apoB-100 pool size (PS) (Δ = -22.5%; P = 0.01). This substitution also reduced low-density lipoprotein cholesterol (LDL-C) (Δ = -7.0%; P = 0.01), non-high-density lipoprotein cholesterol (Δ = -2.5%; P = 0.04), and LDL apoB-100 PS (Δ = -6.0%; P = 0.05). These differences were partially attributed to an increase in LDL apoB-100 FCR (Δ = +1.6%; P = 0.05). The MUFA diet showed reduced sphingolipid concentrations and elevated glycerophospholipid levels compared with the SFA diet.

CONCLUSIONS

This study demonstrated that substituting dietary MUFAs for SFAs decreases LDL-C levels and LDL PS by increasing LDL apoB-100 FCR and results in an overall improved plasma lipidomic profile in individuals with IR-induced lipidemia.

TRIAL REGISTRATION

This trial was registered as clinicaltrials.gov as NCT03872349.

Ipragliflozin and sitagliptin differentially affect lipid and apolipoprotein profiles in type 2 diabetes: the SUCRE study

BACKGROUND

SGLT2 inhibitors and DPP4 inhibitors have been suggested to affect lipid metabolism. However, there are few randomized controlled trials comparing the effects on the lipid metabolism between the two types of antidiabetic drugs. The SUCRE study (UMIN ID: 000018084) was designed to compare the effects of ipragliflozin and sitagliptin on serum lipid and apolipoprotein profiles and other clinical parameters.

METHODS

This is a multicenter, open-label, randomized, controlled trial. Patients with type 2 diabetes (20-74 years old) with HbA1c levels of 7.0-10.5% and serum triglyceride levels of 120-399 mg/dL (1.35-4.50 mmol/L) on diet and/or oral hypoglycemic agents were enrolled. Subjects were randomized to treatment with ipragliflozin (50 mg/day, n = 77) or sitagliptin (50 mg/day, n = 83). Laboratory measurements were performed at 0, 1, 3, and 6 months of treatment.

RESULTS

Ipragliflozin and sitagliptin reduced fasting plasma glucose, glycoalbumin, and HbA1c almost equally. Ipragliflozin increased HDL-C and decreased apo E. Sitagliptin decreased TG, apo B48, CII, and CIII, but increased LDL-C. The between-treatment differences were significant for HDL-C (P = 0.02) and apo B48 (P = 0.006), and nearly significant for apo A1 (P = 0.06). In addition, ipragliflozin reduced body weight, blood pressure, serum liver enzymes, uric acid, and leptin, and increased serum ketones compared with sitagliptin.

CONCLUSIONS

While ipragliflozin and sitagliptin showed similar effects on glycemic parameters, the effects on serum lipid and apolipoprotein profiles were different. Ipragliflozin may have an anti-atherogenic effect through modulation of HDL-C and apo E compared to sitagliptin through TG and apo B48, CII, and CIII in patients with type 2 diabetes.

Incretin hormones and type 2 diabetes

Incretin hormones (glucose-dependent insulinotropic polypeptide [GIP] and glucagon-like peptide-1 [GLP-1]) play a role in the pathophysiology of type 2 diabetes. Along with their derivatives they have shown therapeutic success in type 2 diabetes, with the potential for further improvements in glycaemic, cardiorenal and body weight-related outcomes. In type 2 diabetes, the incretin effect (greater insulin secretory response after oral glucose than with 'isoglycaemic' i.v. glucose, i.e. with an identical glycaemic stimulus) is markedly reduced or absent. This appears to be because of a reduced ability of GIP to stimulate insulin secretion, related either to an overall impairment of beta cell function or to specific defects in the GIP signalling pathway. It is likely that a reduced incretin effect impacts on postprandial glycaemic excursions and, thus, may play a role in the deterioration of glycaemic control. In contrast, the insulinotropic potency of GLP-1 appears to be much less impaired, such that exogenous GLP-1 can stimulate insulin secretion, suppress glucagon secretion and reduce plasma glucose concentrations in the fasting and postprandial states. This has led to the development of incretin-based glucose-lowering medications (selective GLP-1 receptor agonists or, more recently, co-agonists, e.g. that stimulate GIP and GLP-1 receptors). Tirzepatide (a GIP/GLP-1 receptor co-agonist), for example, reduces HbA1c and body weight in individuals with type 2 diabetes more effectively than selective GLP-1 receptor agonists (e.g. semaglutide). The mechanisms by which GIP receptor agonism may contribute to better glycaemic control and weight loss after long-term exposure to tirzepatide are a matter of active research and may change the pessimistic view that developed after the disappointing lack of insulinotropic activity in people with type 2 diabetes when exposed to GIP in short-term experiments. Future medications that stimulate incretin hormone and other receptors simultaneously may have the potential to further increase the ability to control plasma glucose concentrations and induce weight loss.

Novel Antidiabetic Agents and Their Effects on Lipid Profile: A Single Shot for Several Cardiovascular Targets

Type-2 diabetes mellitus (DM) represents one of the most important risk factors for cardiovascular diseases (CVD). Hyperglycemia and glycemic variability are not the only determinant of the increased cardiovascular (CV) risk in diabetic patients, as a frequent metabolic disorder associated with DM is dyslipidemia, characterized by hypertriglyceridemia, decreased high-density lipoprotein (HDL) cholesterol levels and a shift towards small dense low-density lipoprotein (LDL) cholesterol. This pathological alteration, also called diabetic dyslipidemia, represents a relevant factor which could promotes atherosclerosis and subsequently an increased CV morbidity and mortality. Recently, the introduction of novel antidiabetic agents, such as sodium glucose transporter-2 inhibitors (SGLT2i), dipeptidyl peptidase-4 inhibitors (DPP4i) and glucagon-like peptide-1 (GLP-1) receptor agonists (GLP-1 RAs), has been associated with a significant improvement in CV outcomes. Beyond their known action on glycemia, their positive effects on the CV system also seems to be related to an ameliorated lipidic profile. In this context, this narrative review summarizes the current knowledge regarding these novel anti-diabetic drugs and their effects on diabetic dyslipidemia, which could explain the provided global benefit to the cardiovascular system.

Associations between Insulin-Like Growth Factor Binding Protein-2 and lipoprotein kinetics in men

Low circulating concentrations of insulin-like growth factor binding protein-2 (IGFBP-2) have been associated with dyslipidemia, notably with high triglyceride (TG) levels. However, the determinants by which IGFBP-2 influences lipoprotein metabolism, especially that of TG-rich lipoproteins (TRLs), are poorly understood. Here, we aimed to assess the relationships between IGFBP-2 levels and lipoprotein production and catabolism in human subjects. Fasting IGFBP-2 concentrations were measured in the plasma of 219 men pooled from previous lipoprotein kinetics studies. We analyzed production rate and fractional catabolic rates of TRLapoB-48, and LDL-, IDL-, and VLDLapoB-100 by multicompartmental modeling of l-[5,5,5-D3] leucine enrichment data after a 12 h primed constant infusion in individuals kept in a constant nutritional steady state. Subjects had an average BMI of 30 kg/m², plasma IGFBP-2 levels of 157 ng/ml, and TG of 2.2 mmol/l. After adjustments for age and BMI, IGFBP-2 levels were negatively associated with plasma TG (r = −0.29; P < 0.0001) and positively associated with HDL-cholesterol (r = 0.26; P < 0.0001). In addition, IGFBP-2 levels were positively associated with the fractional catabolic rate of VLDLapoB-100 (r = 0.20; P < 0.01) and IDLapoB-100 (r = 0.19; P < 0.05) and inversely with the production rate of TRLapoB-48 (r = −0.28; P < 0.001). These correlations remained statistically significant after adjustments for age, BMI, and the amount of fat given during the tracer infusion. These findings show that the association between low plasma IGFBP-2 and high TG concentrations could be due to both an impaired clearance of apoB-100-containing VLDL and IDL particles and an increased production of apoB-48-containing chylomicrons. Additional studies are necessary to investigate whether and how IGFBP-2 directly impacts the kinetics of TRL.

Liraglutide Increases the Catabolism of Apolipoprotein B100-Containing Lipoproteins in Patients With Type 2 Diabetes and Reduces Proprotein Convertase Subtilisin/Kexin Type 9 Expression

OBJECTIVE

Dyslipidemia observed in type 2 diabetes (T2D) is atherogenic. Important features of diabetic dyslipidemia are increased levels of triglyceride-rich lipoproteins and small dense LDL particles, which all have apolipoprotein B100 (apoB100) as a major apolipoprotein. This prompted us to study the effect of the GLP-1 agonist liraglutide on the metabolism of apoB100-containing lipoproteins.

RESEARCH DESIGN AND METHODS

We performed an in vivo kinetic study with stable isotopes (L-[1-¹³C]leucine) in 10 patients with T2D before and after 6 months of treatment with liraglutide (1.2 mg/day). We also evaluated in mice the effect of liraglutide on the expression of genes involved in apoB100-containing lipoprotein clearance.

RESULTS

In patients with T2D, liraglutide treatment significantly reduced plasma apoB100 (0.93 ± 0.13 vs. 1.09 ± 0.11 g/L, P = 0.011) and fasting triglycerides (1.76 ± 0.37 vs. 2.48 ± 0.69 mmol/L, P = 0.005). The kinetic study showed a significant increase in indirect catabolism of VLDL₁-apoB100 (4.11 ± 1.91 vs. 2.96 ± 1.61 pools/day, P = 0.005), VLDL₂-apoB100 (5.17 ± 2.53 vs. 2.84 ± 1.65 pools/day, P = 0.008), and IDL-apoB100 (5.27 ± 2.77 vs. 3.74 ± 1.85 pools/day, P = 0.017) and in catabolism of LDL-apoB100 (0.72 ± 0.22 vs. 0.56 ± 0.22 pools/day, P = 0.005). In mice, liraglutide increased lipoprotein lipase (LPL) gene expression and reduced proprotein convertase subtilisin/kexin type 9 (PCSK9), retinol-binding protein 4 (RBP4), and tumor necrosis factor-α (TNF-α) gene expression in adipose tissue and decreased PCSK9 mRNA and increased LDL receptor protein expression in liver. In vitro, liraglutide directly reduced the expression of PCSK9 in the liver.

CONCLUSIONS

Treatment with liraglutide induces a significant acceleration of the catabolism of triglyceride-rich lipoproteins (VLDL₁, VLDL₂, IDL) and LDL. Liraglutide modifies the expression of genes involved in apoB100-containing lipoprotein catabolism. These positive effects on lipoprotein metabolism may reduce cardiovascular risk in T2D.

Insights into incretin-based therapies for treatment of diabetic dyslipidemia

Derangements in triglyceride and cholesterol metabolism (dyslipidemia) are major risk factors for the development of cardiovascular diseases in obese and type-2 diabetic (T2D) patients. An emerging class of glucagon-like peptide-1 (GLP-1) analogues and next generation peptide dual-agonists such as GLP-1/glucagon or GLP-1/GIP could provide effective therapeutic options for T2D patients. In addition to their role in glucose and energy homeostasis, GLP-1, GIP and glucagon serve as regulators of lipid metabolism. This review summarizes the current knowledge in GLP-1, glucagon and GIP effects on lipid and lipoprotein metabolism and frames the emerging therapeutic benefits of GLP-1 analogs and GLP-1-based multiagonists as add-on treatment options for diabetes associated dyslipidemia.

Sitagliptin improves plasma apolipoprotein profile in type 2 diabetes: A randomized clinical trial of sitagliptin effect on lipid and glucose metabolism (SLIM) study

AIM

This study aims to evaluate the effect of dipeptidyl peptidase-4 inhibitors on lipid metabolism in patients with type 2 diabetes mellitus (T2D).

METHODS

This is a multicenter, open-labeled, randomized controlled study. T2D patients with HbA1c 6.9-8.9% (52-74 mmol/mol) who were under treatment with sulfonylurea were randomly allocated to either the sitagliptin group or the non-sitagliptin group. Glucose and lipid metabolism parameters including apolipoproteins (apo), sterols, and urinary albumin were assessed at baseline, 3, and 6 months of the treatment.

RESULTS

A total of 164 patients completed the 6-month observation (n = 81 for sitagliptin and n = 83 for non-sitagliptin). HbA1c decreased in the sitagliptin group but not in the non-sitagliptin group. Serum TG and total, LDL and HDL cholesterol levels did not change in either group. Apo B-48, apo CII, and apo CIII levels decreased in the sitagliptin group, but not in the non-sitagliptin group. The change in urinary albumin was significantly different between the groups with a preferable change in the sitagliptin group. There were no changes in serum sterols levels in the two groups.

CONCLUSIONS

The treatment of sitagliptin for 6 months improves the metabolism of glucose and chylomicron and reduces plasma levels of atherogenic lipoproteins in patients with T2D.

Plasma biomarkers of small intestine adaptations in obesity-related metabolic alterations

BACKGROUND

Evidence suggests that pathophysiological conditions such as obesity and type 2 diabetes (T2D) are associated with morphologic and metabolic alterations in the small intestinal mucosa. Exploring these alterations generally requires invasive methods, limiting data acquisition to subjects with enteropathies or undergoing bariatric surgery. We aimed to evaluate small intestine epithelial cell homeostasis in a cohort of men covering a wide range of adiposity and glucose homoeostasis statuses.

METHODS

Plasma levels of citrulline, a biomarker of enterocyte mass, and I-FABP, a biomarker of enterocyte death, were measured by UHPLC‑MS and ELISA in 154 nondiabetic men and 67 men with a T2D diagnosis.

RESULTS

Plasma citrulline was significantly reduced in men with insulin resistance and T2D compared to insulin sensitive men. Decreased citrulline levels were, however, not observed in men with uncontrolled metabolic parameters during T2D. Plasma I-FABP was significantly higher in men with T2D, especially in presence of uncontrolled glycemic and lipid profile parameters. Integration of both parameters, which estimate enterocyte turnover, was associated with glucose homeostasis as well as with T2D diagnosis. Differences in biomarkers levels were independent of age and BMI and glucose filtration rates.

CONCLUSIONS

Our study supports a decreased functional enterocyte mass and an increased enterocyte death rate in presence of metabolic alterations but emphasizes that epithelial cell homeostasis is especially altered in presence of severe insulin resistance and T2D. The marked changes in small intestine cellularity observed in obesity and diabetes are thus suggested to be part of gut dysfunctions, mainly at an advanced stage of the disease.

Pharmacology of dipeptidyl peptidase-4 inhibitors and its use in the management of metabolic syndrome: a comprehensive review on drug repositioning

OBJECTIVES

Despite advances in our understanding of metabolic syndrome (MetS) and the treatment of each of its components separately, currently there is no single therapy approved to manage it as a single condition. Since multi-drug treatment increases drug interactions, decreases patient compliance and increases health costs, it is important to introduce single therapies that improve all of the MetS components.

EVIDENCE ACQUISITION

We conducted a PubMed, Scopus, Google Scholar, Web of Science, US FDA, utdo.ir and clinicaltrial.gov search, gathered the most relevant preclinical and clinical studies that have been published since 2010, and discussed the beneficial effects of dipeptidyl peptidase (DPP)-4 inhibitors to prevent and treat different constituent of the MetS as a single therapy. Furthermore, the pharmacology of DPP-4 inhibitors, focusing on pharmacodynamics, pharmacokinetics, drug interactions and their side effects are also reviewed.

RESULTS

DPP-4 inhibitors or gliptins are a new class of oral anti-diabetic drugs that seem safe drugs with no severe side effects, commonly GI disturbance, infection and inflammatory bowel disease. They increase mass and function of pancreatic β-cells, and insulin sensitivity in liver, muscle and adipose tissue. It has been noted that gliptin therapy decreases dyslipidemia. DPP-4 inhibitors increase fatty oxidation, and cholesterol efflux, and decrease hepatic triglyceride synthase and de novo lipogenesis. They delay gastric emptying time and lead to satiety. Besides, gliptin therapy has anti-inflammatory and anti-atherogenic impacts, and improves endothelial function and reduces vascular stiffness.

CONCLUSION

The gathered data prove the efficacy of DPP-4 inhibitors in managing MetS in some levels beyond anti-diabetic effects. This review could be a lead for designing new DPP-4 inhibitors with greatest effects on MetS in future. Introducing drugs with polypharmacologic effects could increase the patient's compliance and decrease the health cost that there is not in multi-drug therapy. Graphical abstract ᅟ.

Effect of sitagliptin on energy metabolism and brown adipose tissue in overweight individuals with prediabetes: a randomised placebo-controlled trial

AIMS/HYPOTHESIS

The aim of this study was to evaluate the effect of sitagliptin on glucose tolerance, plasma lipids, energy expenditure and metabolism of brown adipose tissue (BAT), white adipose tissue (WAT) and skeletal muscle in overweight individuals with prediabetes (impaired glucose tolerance and/or impaired fasting glucose).

METHODS

We performed a randomised, double-blinded, placebo-controlled trial in 30 overweight, Europid men (age 45.9 ± 6.2 years; BMI 28.8 ± 2.3 kg/m²) with prediabetes in the Leiden University Medical Center and the Alrijne Hospital between March 2015 and September 2016. Participants were initially randomly allocated to receive sitagliptin (100 mg/day) (n = 15) or placebo (n = 15) for 12 weeks, using a randomisation list that was set up by an unblinded pharmacist. All people involved in the study as well as participants were blinded to group assignment. Two participants withdrew from the study prior to completion (both in the sitagliptin group) and were subsequently replaced with two new participants that were allocated to the same treatment. Before and after treatment, fasting venous blood samples and skeletal muscle biopsies were obtained, OGTT was performed and body composition, resting energy expenditure and [¹⁸F] fluorodeoxyglucose ([¹⁸F]FDG) uptake by metabolic tissues were assessed. The primary study endpoint was the effect of sitagliptin on BAT volume and activity.

RESULTS

One participant from the sitagliptin group was excluded from analysis, due to a distribution error, leaving 29 participants for further analysis. Sitagliptin, but not placebo, lowered glucose excursion (-40%; p < 0.003) during OGTT, accompanied by an improved insulinogenic index (+38%; p < 0.003) and oral disposition index (+44%; p < 0.003). In addition, sitagliptin lowered serum concentrations of triacylglycerol (-29%) and very large (-46%), large (-35%) and medium-sized (-24%) VLDL particles (all p < 0.05). Body weight, body composition and energy expenditure did not change. In skeletal muscle, sitagliptin increased mRNA expression of PGC1β (also known as PPARGC1B) (+117%; p < 0.05), a main controller of mitochondrial oxidative energy metabolism. Although the primary endpoint of change in BAT volume and activity was not met, sitagliptin increased [¹⁸F] FDG uptake in subcutaneous WAT (sWAT; +53%; p < 0.05). Reported side effects were mild and transient and not necessarily related to the treatment.

CONCLUSIONS/INTERPRETATION

Twelve weeks of sitagliptin in overweight, Europid men with prediabetes improves glucose tolerance and lipid metabolism, as related to increased [¹⁸F] FDG uptake by sWAT, rather than BAT, and upregulation of the mitochondrial gene PGC1β in skeletal muscle. Studies on the effect of sitagliptin on preventing or delaying the progression of prediabetes into type 2 diabetes are warranted.

TRIAL REGISTRATION

ClinicalTrials.gov NCT02294084.

FUNDING

This study was funded by Merck Sharp & Dohme Corp, Dutch Heart Foundation, Dutch Diabetes Research Foundation, Ministry of Economic Affairs and the University of Granada.

Differential associations between plasma concentrations of insulin and glucose and intestinal expression of key genes involved in chylomicron metabolism

The mechanisms underlying the oversecretion of apolipoprotein (apo)B-48-containing triglyceride-rich lipoproteins (TRL) in insulin-resistance (IR) states in humans remain to be fully understood. The objective of this study was to evaluate the association between the plasma levels of insulin and glucose and the intestinal expression of key genes involved in chylomicron metabolism in a large sample of nondiabetic men displaying various degrees of IR. Duodenal biopsies were obtained by gastroduodenoscopy in 127 men free of intestinal disease. Gene expression was measured using quantitative PCR in duodenal samples. Plasma insulin and glucose concentrations were measured in the fasting state. Postprandial TRL apoB-48 kinetics were measured using a primed-constant infusion of l-[5,5,5-D₃]leucine for 12 h in a subgroup of 75 subjects maintained in a constant fed state. Plasma insulin levels were negatively associated with intestinal expression of ACS1 (standard β = -0.20, P = 0.007), DGAT1 (β = -0.18, P = 0.001), DGAT2 (β = -0.20, P = 0.02), and MTP (β = -0.27, P = 0.0005), whereas glucose levels were positively associated with MTP expression (β = 0.15, P = 0.04) independent of age, BMI, waist circumference, dietary intake, and duodenal expression of SREBP1c. Insulin levels, but not glucose concentrations, were positively correlated with postprandial TRL apoB-48 production rate ( r = 0.24, P = 0.04) and pool size ( r = 0.27, P = 0.03). In conclusion, plasma insulin and glucose levels are differentially associated with the expression of key genes involved in chylomicron metabolism. These results suggest that alterations in intestinal lipoprotein metabolism associated with IR may be regulated by plasma levels of both insulin and glucose concurrently and are therefore likely modified by the onset of insulin insufficiency. NEW & NOTEWORTHY We demonstrate that plasma insulin and glucose levels are differentially associated with the expression of key genes involved in chylomicron metabolism in men. For instance, intestinal expression of MTP is negatively associated with plasma insulin concentrations and positively associated with plasma glucose concentrations. Alterations in intestinal lipoprotein metabolism associated with insulin resistance may be regulated by plasma levels of both insulin and glucose concurrently and are therefore likely modified by the onset of insulin insufficiency.

Plasma PCSK9 correlates with apoB-48-containing triglyceride-rich lipoprotein production in men with insulin resistance

Intestinal triglyceride (TG)-rich lipoproteins (TRLs) are important in the pathogenesis of atherosclerosis in insulin resistance (IR). We investigated the association of plasma proprotein convertase subtilisin/kexin type 9 (PCSK9) concentrations with apoB-48-containing TRL metabolism in 148 men displaying various degrees of IR by measuring in vivo kinetics of TRL apoB-48 during a constant-fed state after a primed-constant infusion of L-[5,5,5-D3]leucine. Plasma PCSK9 concentrations positively correlated with TRL apoB-48 pool size (r = 0.31, P = 0.0002) and production rate (r = 0.24, P = 0.008) but not the fractional catabolic rate (r = -0.04, P = 0.6). Backward stepwise multiple linear regression analysis identified PCSK9 concentrations as a positive predictor of TRL apoB-48 production rate (standard β = +0.20, P = 0.007) independent of BMI, age, T2D/metformin use, dietary fat intake during the kinetic study, and fasting concentrations of TGs, insulin, glucose, LDL cholesterol, or C-reactive protein. We also assessed intestinal expression of key genes involved in chylomicron processing from duodenal samples of 71 men. Expression of PCSK9 and HMG-CoAR genes was positively associated (r = 0.43, P = 0.002). These results support PCSK9 association with intestinal secretion and plasma overaccumulation of TRL apoB-48 in men with IR.

The effects of add-on exenatide to insulin on glycemic variability and hypoglycemia in patients with type 1 diabetes mellitus

OBJECTIVE

To investigate the effect of add-on exenatide to insulin on glycemic excursion and the counter-regulatory hormone in response to hypoglycemia in patients with type 1 diabetes mellitus (T1DM).

METHODS

30 patients with T1DM were recruited and randomly assigned to exenatide + insulin-treated group (group 1, n = 15) or insulin-only-treated group (group 2, n = 15) for 4 weeks. All patients had continuous glucose monitor system (CGMS) applied at before (week-0) and after (week-4) treatment to evaluate the glycemic variability. All patients had an arginine-stimulated test at before and after treatment. Six patients from each group also had hypoglycemic clamp test to assess counter-regulatory hormone level.

RESULTS

Patients in the exenatide group had significant reductions in body weight, body mass index (BMI), total insulin dose, bolus insulin dose, fructosamine, and glycemic excursion after 4 weeks' treatment. Compared with patients in group 2, the mean amplitude of glycemic excursion (MAGE) and coefficient of variation (CV) of exenatide group decreased significantly. Similarly, a significant decrease of glucagon (GLC) in the arginine-stimulated test was found in group 1. No significant changes of GLC, growth hormone (GH), cortisol (COR), epinephrine (E), and norepinephrine (NE) were found in both groups during hypoglycemia clamp test. However, patients who had residual islet function in group 1 showed an upward trend of basic C-peptide (C-P) and GLC during the hypoglycemia period.

CONCLUSION

Although exenatide could inhibit glucagon secretion during euglycemia or hyperglycemia in patients with T1DM, it has no effect on GLC and counter-regulatory hormones during hypoglycemia clamp in patients with no functional residual islet test.

Protective effects of dietary polyphenols from black soybean seed coats on islet and renal function in streptozotocin-induced diabetic rats

BACKGROUND

The aim of this study was to investigate the antidiabetic effects of the crude polyphenol extract (BSCP) from black soybean seed coats (BSC) and the whole flour of BSC and illustrate the mechanism in terms of islet and renal protection.

RESULTS

BSCP and BSC effectively controlled the increased blood glucose level and impaired glucose tolerance in streptozotocin (STZ)-induced diabetic rats after 8 weeks of treatment. They increased the concentrations of serum insulin, C-peptide and Glp-1 (P < 0.05) by improving the STZ-induced damage of islet β-cells and increasing their insulin expression (P < 0.05). Lipid profiles and antioxidant activities were also improved. Moreover, BSCP and BSC tended to decrease serum creatinine (0.05 < P < 0.1), and blood urea nitrogen was decreased by BSC significantly (P < 0.05). They also led to significantly lower glomerular volume (P < 0.05).

CONCLUSION

Long-term intervention with BSC at a low dose of polyphenols plays a role in controlling blood glucose and lipids levels by promoting insulin secretion and restoring islet β-cell function, the same as BSCP. These benefits are accompanied by their potential protection of diabetic renal dysfunction. BSCP is mainly responsible for the antidiabetic effect of BSC. © 2017 Society of Chemical Industry.

Substitution of dietary ω-6 polyunsaturated fatty acids for saturated fatty acids decreases LDL apolipoprotein B-100 production rate in men with dyslipidemia associated with insulin resistance: a randomized controlled trial

Background

The substitution of omega (ω)-6 (n-6) polyunsaturated fatty acids (PUFAs) for saturated fatty acids (SFAs) is advocated in cardiovascular disease prevention. The impact of this substitution on lipoprotein metabolism in subjects with dyslipidemia associated with insulin resistance (IR) remains unknown.

Objective

In men with dyslipidemia and IR, we evaluated the impact of substituting ω-6 PUFAs for SFAs on the in vivo kinetics of apolipoprotein (apo) B-containing lipoproteins and on the intestinal expression of key genes involved in lipoprotein metabolism.

Design

Dyslipidemic and IR men (n = 36) were recruited for this double-blind, randomized, crossover, controlled trial. Subjects consumed, in a random order, a fully controlled diet rich in SFAs (SFAs: 13.4% of energy; ω-6 PUFAs: 4.0%) and a fully controlled diet rich in ω-6 PUFAs (SFAs: 6.0%; ω-6 PUFAs: 11.3%) for periods of 4 wk, separated by a 4-wk washout period. At the end of each diet, the in vivo kinetics of apoB-containing lipoproteins were measured and the intestinal expression of key genes involved in lipoprotein metabolism was quantified in duodenal biopsies taken from each participant.

Results

The substitution of ω-6 PUFAs for SFAs had no impact on TRL apoB-48 fractional catabolic rate (Δ = -3.8%, P = 0.7) and production rate (Δ = +1.2%, P = 0.9), although it downregulated the intestinal expression of the microsomal triglyceride transfer protein (Δ = -18.4%, P = 0.006) and apoB (Δ = -16.6%, P = 0.005). The substitution of ω-6 PUFAs for SFAs decreased the LDL apoB-100 pool size (Δ = -7.8%; P = 0.005). This difference was attributed to a reduction in the LDL apoB-100 production rate after the substitution of ω-6 PUFAs for SFAs (Δ = -10.0%; P = 0.003).

Conclusions

This study demonstrates that the substitution of dietary ω-6 PUFAs for SFAs decreases the production and number of LDL particles in men with dyslipidemia and IR. This trial was registered at clinicaltrials.gov as NCT01934543.

C-reactive protein levels are inversely correlated with the apolipoprotein B-48-containing triglyceride-rich lipoprotein production rate in insulin resistant men

The pro-inflammatory state and elevated plasma levels of post-prandial triglycerides (TG) are associated with increased cardiovascular disease risk. Recent studies suggested that the increase in the production rate of post-prandial lipoproteins observed in patients with insulin resistance (IR) may be caused, at least in part, by the dysregulation of intestinal insulin sensitivity triggered by inflammation.

OBJECTIVE

The objective of the present study was to evaluate the association between IR, plasma C-reactive protein (CRP) levels and the kinetics of TG-rich lipoprotein (TRL) containing apolipoprotein (apo) B-48 in a large sample of insulin sensitive (IS) and IR men.

METHODS

The in vivo kinetics of TRL apoB-48 were measured in 151 men following a primed-constant infusion of l-[5,5,5-D₃]leucine. IR subjects (n=91) were characterized by fasting TG levels ≥1.5mmol/L and an index of homeostasis model assessment of IR (HOMA-IR)≥2.5 or type 2 diabetes, while IS subjects (n=24) were characterized by an HOMA-IR index <2.5 and TG levels <1.5mmol/L.

RESULTS

IR subjects had higher TRL apoB-48 production rate (+202%; P<0.0001) and CRP levels (+51%; P=0.01) than IS subjects. TRL apoB-48 production rate and CRP levels were inversely correlated in IR subjects (r=-0.32; P=0.002). IR subjects with CRP levels above the median (2.20mg/L) had lower TRL apoB-48 production rate than IR subjects with CRP levels below the median (Δ=-24%; P<0.05).

CONCLUSION

Our results confirm that IR is associated with increased TRL apoB-48 secretion and suggest that a higher inflammatory status is associated with decreased TRL apoB-48 secretion among IR subjects.

Effects of gemigliptin, a dipeptidyl peptidase-4 inhibitor, on lipid metabolism and endotoxemia after a high-fat meal in patients with type 2 diabetes

We aimed to investigate the effects of gemigliptin, a dipeptidyl peptidase-4 inhibitor, on postprandial lipoprotein levels and endotoxemia in a randomized, double-blind, placebo-controlled, crossover study. Ten people with type 2 diabetes mellitus (T2DM), inadequately controlled with oral antidiabetic medications and/or lifestyle modification, were randomized to gemigliptin or placebo for 4 weeks. At the end of each treatment phase, the study participants underwent a high-fat meal tolerance test and needle aspiration of abdominal subcutaneous adipose tissue. The median (range) fasting and total area under the curve of apolipoprotein B48 (ApoB48) were significantly lower with gemigliptin than with placebo (2.9 [1.5-15.8] µg/mL vs 4.2 [1.3-23.4] µg/mL; P = .020; 35.3 [14.4-87.4] µg/mL × hour vs 42.2 [17.5-109.0] µg/mL × hour; P = .020, respectively), whereas apolipoprotein B100 showed no significant difference. Serum endotoxin levels were undetectable in 70% of the samples, so we were not able to evaluate the effect of gemigliptin on endotoxemia. The gene expression of inflammatory cytokines in subcutaneous adipose tissue was not affected by gemigliptin. Gemigliptin reduced ApoB48 levels after a high-fat meal in participants with T2DM. Whether systemic endotoxin levels can be reduced by gemigliptin requires further investigation.

Minor Contribution of Endogenous GLP-1 and GLP-2 to Postprandial Lipemia in Obese Men

Context

Glucose and lipids stimulate the gut-hormones glucagon-like peptide (GLP)-1, GLP-2 and glucose-dependent insulinotropic polypeptide (GIP) but the effect of these on human postprandial lipid metabolism is not fully clarified.

Objective

To explore the responses of GLP-1, GLP-2 and GIP after a fat-rich meal compared to the same responses after an oral glucose tolerance test (OGTT) and to investigate possible relationships between incretin response and triglyceride-rich lipoprotein (TRL) response to a fat-rich meal.

Design

Glucose, insulin, GLP-1, GLP-2 and GIP were measured after an OGTT and after a fat-rich meal in 65 healthy obese (BMI 26.5–40.2 kg/m²) male subjects. Triglycerides (TG), apoB48 and apoB100 in TG-rich lipoproteins (chylomicrons, VLDL₁ and VLDL₂) were measured after the fat-rich meal.

Main Outcome Measures

Postprandial responses (area under the curve, AUC) for glucose, insulin, GLP-1, GLP-2, GIP in plasma, and TG, apoB48 and apoB100 in plasma and TG-rich lipoproteins.

Results

The GLP-1, GLP-2 and GIP responses after the fat-rich meal and after the OGTT correlated strongly (r = 0.73, p<0.0001; r = 0.46, p<0.001 and r = 0.69, p<0.001, respectively). Glucose and insulin AUCs were lower, but the AUCs for GLP-1, GLP-2 and GIP were significantly higher after the fat-rich meal than after the OGTT. The peak value for all hormones appeared at 120 minutes after the fat-rich meal, compared to 30 minutes after the OGTT. After the fat-rich meal, the AUCs for GLP-1, GLP-2 and GIP correlated significantly with plasma TG- and apoB48 AUCs but the contribution was very modest.

Conclusions

In obese males, GLP-1, GLP-2 and GIP responses to a fat-rich meal are greater than following an OGTT. However, the most important explanatory variable for postprandial TG excursion was fasting triglycerides. The contribution of endogenous GLP-1, GLP-2 and GIP to explaining the variance in postprandial TG excursion was minor.

Gliptins and Cardiovascular Outcomes: A Comparative and Critical Analysis after TECOS

The issue related to macrovascular outcomes and intensive glycemic control was hotly debated after the publication of landmark trials like ACCORD, ADVANCE, and VADT. The only benefits seem to come from intervening early on in the disease process as indicated by the 10-year UKPDS follow-up. To complicate matters USFDA made it mandatory for modern drugs to conduct cardiovascular safety trials in high-risk populations after the 2008 rosiglitazone scare. This led to all the modern group of drugs designing cardiovascular safety trials (gliptins, GLP-1 agonists, and SGLT-2 inhibitors) to meet USFDA regulatory requirements. We saw publication of the first 2 randomized trials with gliptins published a year and a half back. On the face value SAVOR TIMI and EXAMINE satisfied the primary composite CV end-points. However, issues related to significant increase in heart failure and all-cause 7-day on-treatment mortality created a lot of confusion. FDA reanalysis of these data (especially SAVOR) raises a lot of doubts as far as CV safety of these groups of drugs was concerned. Hence, all eyes were on TECOS, which was published this year. We take a microscopic look at these trials trying to understand where we stand as from now on this issue.

Gut Peptides Are Novel Regulators of Intestinal Lipoprotein Secretion: Experimental and Pharmacological Manipulation of Lipoprotein Metabolism

Individuals with metabolic syndrome and frank type 2 diabetes are at increased risk of atherosclerotic cardiovascular disease, partially due to the presence of lipid and lipoprotein abnormalities. In these conditions, the liver and intestine overproduce lipoprotein particles, exacerbating the hyperlipidemia of fasting and postprandial states. Incretin-based, antidiabetes therapies (i.e., glucagon-like peptide [GLP]-1 receptor agonists and dipeptidyl peptidase-4 inhibitors) have proven efficacy for the treatment of hyperglycemia. Evidence is accumulating that these agents also improve fasting and postprandial lipemia, the latter more significantly than the former. In contrast, the gut-derived peptide GLP-2, cosecreted from intestinal L cells with GLP-1, has recently been demonstrated to enhance intestinal lipoprotein release. Understanding the roles of these emerging regulators of intestinal lipoprotein secretion may offer new insights into the regulation of intestinal lipoprotein assembly and secretion and provide new opportunities for devising novel strategies to attenuate hyperlipidemia, with the potential for cardiovascular disease reduction.

Anti-diabetic effects of shubat in type 2 diabetic rats induced by combination of high-glucose-fat diet and low-dose streptozotocin

ETHNOPHARMACOLOGICAL RELEVANCE

Shubat, probiotic fermented camel milk, has been used both as a drink with ethnic flavor and a medicine among Kazakh population for diabetic patients. Kazakh people have lower diabetic prevalence and impaired fasting glucose (IFG) than do other ethnic groups living in Xinjiang China, which might be related to the beneficial properties of shubat. We therefore prepared shubat in laboratory and tested anti-diabetic activity and evaluated its possible hypolipidemic and renoprotective effects in type 2 diabetic rats.

MATERIALS AND METHODS

Type 2 diabetic rats were induced by an administration of high-glucose-fat diet for 6 weeks and an intraperitoneal injection of streptozotocin (STZ, 30mg/kg). Diabetic rats were divided randomly into four groups and treated for 28 days with sitagliptin (30mg/kg) or shubat (6.97×10(6) lactic acid bacteria+2.20×10(4) yeasts) CFU/mL, (6.97×10(7) lactic acid bacteria+2.20×10(5) yeasts) CFU/mL and (6.97×10(8) lactic acid bacteria+2.20×10(6) yeasts) CFU/mL. In addition, a normal control group and a diabetic control group were used for comparison. All drugs were given orally once daily 10mL/kg for 4 weeks. Fasting blood glucose (FBG) and body weight (BW) were measured before treatment and every week thereafter. Total cholesterol (TC), triglycerides (TG), low-density lipoprotein cholesterol (LDL-c), high density lipoprotein cholesterol (HDL-c), serum creatinine (SCr), blood urea nitrogen (BUN), C-peptide, glycated hemoglobin (HbAlc), glucagon-like peptide-1 (GLP-1) levels and pancreas tissue sections were tested after 4 weeks.

RESULTS

Shubat demonstrated positive hypoglycemic activity on FBG, HbAlc, C-peptide and GLP-1 levels, high dose shubat decreased FBG (P<0.01) and HbAlc (P<0.05), increased C-peptide (P<0.05) and GLP-1 (P<0.01), decreased serum TC, TG, LDL-c (P<0.05), increased HDL-c (P<0.01), and improved the reduction of body weight as well as decreased SCr and BUN levels (P<0.01) compared to diabetic controls. Histological analysis showed shubat protected the function of islets of type 2 diabetic rats.

CONCLUSION

The results of this study indicate that shubat has significant hypoglycemic potential in T2D rats and may modulate lipid metabolism and protect renal function in the type 2 diabetic condition, which might be related to various probiotics acting through promoting the release of GLP-1 and improving the function of β-cells.

New Insights into the Regulation of Chylomicron Production

Dietary lipids are efficiently absorbed by the small intestine, incorporated into triglyceride-rich lipoproteins (chylomicrons), and transported in the circulation to various tissues. Intestinal lipid absorption and mobilization and chylomicron synthesis and secretion are highly regulated processes. Elevated chylomicron production rate contributes to the dyslipidemia seen in common metabolic disorders such as insulin-resistant states and type 2 diabetes and likely increases the risk for atherosclerosis seen in these conditions. An in-depth understanding of the regulation of chylomicron production may provide leads for the development of drugs that could be of therapeutic utility in the prevention of dyslipidemia and atherosclerosis. Chylomicron secretion is subject to regulation by various factors, including diet, body weight, genetic variants, hormones, nutraceuticals, medications, and emerging interventions such as bariatric surgical procedures. In this review we discuss the regulation of chylomicron production, mechanisms that underlie chylomicron dysregulation, and potential avenues for future research.