GLP-1 reduces intestinal lymph flow, triglyceride absorption, and apolipoprotein production in rats

Transport functions of intestinal lymphatic vessels

Lymphatic vessels are crucial for fluid absorption and the transport of peripheral immune cells to lymph nodes. However, in the small intestine, the lymphatic fluid is rich in diet-derived lipids incorporated into chylomicrons and gut-specific immune cells. Thus, intestinal lymphatic vessels have evolved to handle these unique cargoes and are critical for systemic dietary lipid delivery and metabolism. This Review covers mechanisms of lipid absorption from epithelial cells to the lymphatics as well as unique features of the gut microenvironment that affect these functions. Moreover, we discuss details of the intestinal lymphatics in gut immune cell trafficking and insights into the role of inter-organ communication. Lastly, we highlight the particularities of fat absorption that can be harnessed for efficient lipid-soluble drug distribution for novel therapies, including the ability of chylomicron-associated drugs to bypass first-pass liver metabolism for systemic delivery. In all, this Review will help to promote an understanding of intestinal lymphatic-systemic interactions to guide future research directions.

Bile acids and incretins as modulators of obesity-associated atherosclerosis

Obesity is one of the major global health concerns of the 21st century, associated with many comorbidities such as type 2 diabetes mellitus (T2DM), metabolic dysfunction-associated steatotic liver disease, and early and aggressive atherosclerotic cardiovascular disease, which is the leading cause of death worldwide. Bile acids (BAs) and incretins are gut hormones involved in digestion and absorption of fatty acids, and insulin secretion, respectively. In recent years BAs and incretins are increasingly recognized as key signaling molecules, which target multiple tissues and organs, beyond the gastro-intestinal system. Moreover, incretin-based therapy has revolutionized the treatment of T2DM and obesity. This mini review highlights the current knowledge about dysregulations in BA homeostasis in obesity with a special focus on atherosclerosis as well as athero-modulating roles of incretins and currently available incretin-based therapies.

Are the lipid-lowering effects of incretin-based therapies relevant for cardiovascular benefit?

PURPOSE OF REVIEW

This review examines the impact of glucagon-like peptide 1 receptor agonists (GLP-1RAs) on lipid profiles in individuals with type 2 diabetes mellitus and/or obesity, crucial for optimizing cardiovascular risk management.

RECENT FINDINGS

GLP-1RAs affect lipid levels by reducing intestinal apolipoprotein B48 production and mesenteric lymph flow, while increasing catabolism of apolipoprotein B100. It remains unknown whether these effects are direct or indirect, but the improvements in lipid levels are strongly correlated to the drug-induced weight loss. Clinical trials demonstrate improvements in lipid profiles, with different effects per agent and dose. We deem it unlikely that improved lipid levels are sufficient to explain the beneficial effects of GLP-1RA on cardiovascular risk, especially given the improvement of many other risk factors (body weight, glycemic control, inflammation) while using these agents. Posthoc mediation analyses of large cardiovascular outcome trials may shed some light on the relative importance of each risk factor.

SUMMARY

GLP-1RAs improve lipid profiles in clinical trials, but their complete cardiovascular benefits likely involve multifactorial mechanisms beyond lipid modulation.

Enteroendocrine cells regulate intestinal homeostasis and epithelial function

Enteroendocrine cells (EECs) are well-known for their systemic hormonal effects, especially in the regulation of appetite and glycemia. Much less is known about how the products made by EECs regulate their local environment within the intestine. Here, we focus on paracrine interactions between EECs and other intestinal cells as they regulate three essential aspects of intestinal homeostasis and physiology: 1) intestinal stem cell function and proliferation; 2) nutrient absorption; and 3) mucosal barrier function. We also discuss the ability of EECs to express multiple hormones, describe in vitro and in vivo models to study EECs, and consider how EECs are altered in GI disease.

Glucagon-like peptide (GLP)-1 regulation of lipid and lipoprotein metabolism

Metabolic health is highly dependent on intestinal and hepatic handling of dietary and endogenous lipids and lipoproteins. Disorders of lipid and lipoprotein metabolism are commonly observed in patients with insulin resistant states such as obesity, metabolic syndrome, and type 2 diabetes. Evidence from both animal models and human studies indicates that a major underlying factor in metabolic or diabetic dyslipidemia is the overproduction of hepatic and intestinal apolipoprotein (apo)B-containing lipoprotein particles. These particles are catabolized down into highly proatherogenic remnants, which can be taken up into the arterial intima and promote plaque development. Several gut-derived peptides have been identified as key regulators of energy metabolism; one such peptide is the incretin hormone glucagon-like peptide (GLP)-1. Our laboratory has previously demonstrated that GLP-1 can signal both centrally and peripherally to reduce postprandial and fasting lipoprotein secretion. Moreover, we have demonstrated that GLP-1 receptor (GLP-1R) agonists can ameliorate diet-induced dyslipidemia. Recently, we published evidence for a novel vagal neuroendocrine signalling pathway by which native GLP-1 may exert its anti-lipemic effects. Furthermore, we demonstrated a novel role for other gut-derived peptides in regulating intestinal lipoprotein production. Overall, ample evidence supports a key role for GLP-1R on the portal vein afferent neurons and nodose ganglion in modulating intestinal fat absorption and lipoprotein production and identifies other gut-derived peptides as novel regulators of postprandial lipemia. Insights from these data may support identification of potential drug targets and the development of new therapeutics targeting treatment of diabetic dyslipidemia.

Improvement of Theaflavins on Glucose and Lipid Metabolism in Diabetes Mellitus

In diabetes mellitus, disordered glucose and lipid metabolisms precipitate diverse complications, including nonalcoholic fatty liver disease, contributing to a rising global mortality rate. Theaflavins (TFs) can improve disorders of glycolipid metabolism in diabetic patients and reduce various types of damage, including glucotoxicity, lipotoxicity, and other associated secondary adverse effects. TFs exert effects to lower blood glucose and lipids levels, partly by regulating digestive enzyme activities, activation of OATP-MCT pathway and increasing secretion of incretins such as GIP. By the Ca2+-CaMKK ꞵ-AMPK and PI3K-AKT pathway, TFs promote glucose utilization and inhibit endogenous glucose production. Along with the regulation of energy metabolism by AMPK-SIRT1 pathway, TFs enhance fatty acids oxidation and reduce de novo lipogenesis. As such, the administration of TFs holds significant promise for both the prevention and amelioration of diabetes mellitus.

The comparison of the antidiabetic effects of exenatide, empagliflozin, quercetin, and combination of the drugs in type 2 diabetic rats

BACKGROUND

Type 2 diabetes, a metabolic disease that involves extended treatment, is rapidly increasing in humans and animals worldwide.

OBJECTIVES

This study aimed to compare monotherapy and combined therapy of exenatide, empagliflozin, and quercetin in 67 Wistar Albino male rats.

METHODS

The animals were divided into the following seven groups: healthy control, diabetes control, diabetes + sham, diabetes + exenatide (10 μg/kg), diabetes + empagliflozin (50 mg/kg), diabetes + quercetin (50 mg/kg), and diabetes + combination treatment. The treatments were continued for 8 weeks.

RESULTS

At the end of the experiment, glucose and HbA1c levels decreased with all monotherapy treatments and the combination treatments, while insulin levels increased with exenatide and combined treatments. Adiponectin levels increased with empagliflozin, quercetin, and combined treatments, while leptin levels decreased only with combined treatments. All monotherapies caused an increase in total antioxidant levels. Exenatide and quercetin treatments reduced low-density lipoprotein (LDL) levels; therewithal, exenatide and combined treatments increased high-density lipoprotein (HDL) levels. Triglyceride levels decreased in all treatment groups. The homeostatic model assessment for insulin resistance (HOMA-IR) level decreased with the combined treatment; on the contrary, the homeostatic model assessment for β-cell activity (HOMA-β) level increased with empagliflozin, exenatide, and combined treatments.

CONCLUSION

In conclusion, the antidiabetic effects of exenatide were more pronounced than empagliflozin and quercetin, however, the combined treatment had better antidiabetic and antihyperlipidemic effects than monotherapies. Quercetin could be a supportive or food supplement antidiabetic agent. The exenatide treatment can be recommended for monotherapy in type 2 patients, and the combination of empagliflozin, exenatide, and quercetin may be effective in diabetic patients who need combined therapy.

The chondrichthyan glucagon-like peptide 3 regulates hepatic ketone metabolism in the Pacific spiny dogfish Squalus suckleyi

Chondrichthyans have a novel proglucagon-derived peptide, glucagon-like peptide (GLP)-3, in addition to GLP-1 and GLP-2 that occur in other vertebrates. Given that the GLPs are important regulators of metabolic homeostasis across vertebrates, we sought to investigate whether GLP-3 displays functional actions on metabolism within a representative chondrichthyan, the Pacific spiny dogfish Squalus suckleyi. There were no observed effects of GLP-3 perfusion (10 nM for 15 min) on the rate of glucose or oleic acid acquisition at the level of the spiral valve nor were there any measured effects on intermediary metabolism within this tissue. Despite no effects on apparent glucose transport or glycolysis in the liver, a significant alteration to ketone metabolism occurred. Firstly, ketone flux through the perfused liver switched from a net endogenous production to consumption following hormone application. Accompanying this change, significant increases in mRNA transcript abundance of putative ketone transporters and in the activity of β-hydroxybutyrate dehydrogenase (a key enzyme regulating ketone flux in the liver) were observed. Overall, while these results show effects on hepatic metabolism, the physiological actions of GLP are distinct between this chondrichthyan and those of GLP-1 on teleost fishes. Whether this is the result of the particular metabolic dependency on ketone bodies in chondrichthyans or a differential function of a novel GLP remains to be fully elucidated.

Hepatocyte-derived DPP4 regulates portal GLP-1 bioactivity, modulates glucose production, and when absent influences NAFLD progression

Elevated circulating dipeptidyl peptidase-4 (DPP4) is a biomarker for liver disease, but its involvement in gluconeogenesis and metabolic associated fatty liver disease progression remains unclear. Here, we identified that DPP4 in hepatocytes but not TEK receptor tyrosine kinase-positive endothelial cells regulates the local bioactivity of incretin hormones and gluconeogenesis. However, the complete absence of DPP4 (Dpp4-/-) in aged mice with metabolic syndrome accelerates liver fibrosis without altering dyslipidemia and steatosis. Analysis of transcripts from the livers of Dpp4-/- mice displayed enrichment for inflammasome, p53, and senescence programs compared with littermate controls. High-fat, high-cholesterol feeding decreased Dpp4 expression in F4/80+ cells, with only minor changes in immune signaling. Moreover, in a lean mouse model of severe nonalcoholic fatty liver disease, phosphatidylethanolamine N-methyltransferase mice, we observed a 4-fold increase in circulating DPP4, in contrast with previous findings connecting DPP4 release and obesity. Last, we evaluated DPP4 levels in patients with hepatitis C infection with dysglycemia (Homeostatic Model Assessment of Insulin Resistance > 2) who underwent direct antiviral treatment (with/without ribavirin). DPP4 protein levels decreased with viral clearance; DPP4 activity levels were reduced at long-term follow-up in ribavirin-treated patients; but metabolic factors did not improve. These data suggest elevations in DPP4 during hepatitis C infection are not primarily regulated by metabolic disturbances.

Intestinal lipid absorption and transport in type 2 diabetes

Postprandial hyperlipidaemia is an important feature of diabetic dyslipidaemia and plays an important role in the development of cardiovascular disease in individuals with type 2 diabetes. Postprandial hyperlipidaemia in type 2 diabetes is secondary to increased chylomicron production by the enterocytes and delayed catabolism of chylomicrons and chylomicron remnants. Insulin and some intestinal hormones (e.g. glucagon-like peptide-1 [GLP-1]) influence intestinal lipid metabolism. In individuals with type 2 diabetes, insulin resistance and possibly reduced GLP-1 secretion are involved in the pathophysiology of postprandial hyperlipidaemia. Several factors are involved in the overproduction of chylomicrons: (1) increased expression of microsomal triglyceride transfer protein, which is a key enzyme in chylomicron synthesis; (2) higher stability and availability of apolipoprotein B-48; and (3) increased de novo lipogenesis. Individuals with type 2 diabetes present with disorders of cholesterol metabolism in the enterocytes with reduced absorption and increased synthesis. The increased production of chylomicrons in type 2 diabetes is also associated with a reduction in their catabolism, mostly because of a reduction in activity of lipoprotein lipase. Modification of the microbiota, which is observed in type 2 diabetes, may also generate disorders of intestinal lipid metabolism, but human data remain limited. Some glucose-lowering treatments significantly influence intestinal lipid absorption and transport. Postprandial hyperlipidaemia is reduced by metformin, pioglitazone, alpha-glucosidase inhibitors, dipeptidyl peptidase 4 inhibitors and GLP-1 agonists. The most pronounced effect is observed with GLP-1 agonists, which reduce chylomicron production significantly in individuals with type 2 diabetes and have a direct effect on the intestine by reducing the expression of genes involved in intestinal lipoprotein metabolism. The effect of sodium-glucose cotransporter 2 inhibitors on intestinal lipid metabolism needs to be clarified.

The Effect of GLP-1 Receptor Agonists on Postprandial Lipaemia

PURPOSE OF REVIEW

To review the currently available data on the effect of Glucagon-like peptide 1 receptor agonists (GLP-1 RAs) on postprandial lipaemia.

RECENT FINDINGS

Out of the available studies that examined the respective lipid parameter, exenatide reduced postprandial triacyglycerol (TAG) in 4/6, apolipoprotein B-48 in 3/3, non-esterified fatty acids in 2/2, and apolipoprotein C-III and very low-density lipoprotein cholesterol (VLDL-C) in 1/1 studies. Liraglutide reduced postprandial TAG in 2/2, apolipoprotein B-48 in 3/3 and apolipoprotein C-III, chylomicron-TAG and VLDL₁-TAG in 1/1 studies. Lixisenatide reduced postprandial chylomicron-TAG and apolipoprotein B-48 in 1 study. Semaglutide reduced postprandial TAG, apolipoprotein B-48 and VLDL in 1 study. Dulaglutide reduced postprandial apolipoprotein B-48 in 1 study. GLP-1 RAs have consistent beneficial effects on postprandial lipaemia with most of the data coming from studies with exenatide and liraglutide. Reduction of postprandial lipaemia might be one of the mechanisms behind the pleiotropic effects of GLP-1 RAs.

The Impact of Incretin-Based Medications on Lipid Metabolism

Pathophysiological pathways that are induced by chronic hyperglycemia negatively impact lipid metabolism. Thus, diabetes is commonly accompanied by varying degrees of dyslipidemia which is itself a major risk factor for further macro- and microvascular diabetes complications such as atherosclerosis and nephropathy. Therefore, normalizing lipid metabolism is an attractive goal for therapy in patients with diabetes. Incretin-based medications are a novel group of antidiabetic agents with potent hypoglycemic effects. While the impact of incretins on glucose metabolism is clear, recent evidence indicates their positive modulatory roles on various aspects of lipid metabolism. Therefore, incretins may offer additional beneficial effects beyond that of glucose normalization. In the current review, how these antidiabetic medications can regulate lipid homeostasis and the possible cellular pathways involved are discussed, incorporating related clinical evidence about incretin effects on lipid homeostasis.

New Insights of Anti-Hyperglycemic Agents and Traditional Chinese Medicine on Gut Microbiota in Type 2 Diabetes

Type 2 diabetes mellitus (T2DM) is a widespread metabolic disease characterized by chronic hyperglycemia. Human microbiota, which is regarded as a “hidden organ”, plays an important role in the initiation and development of T2DM. In addition, anti-hyperglycemic agents and traditional Chinese medicine may affect the composition of gut microbiota and consequently improve glucose metabolism. However, the relationship between gut microbiota, T2DM and anti-hyperglycemic agents or traditional Chinese medicine is poorly understood. In this review, we summarized pre-clinical and clinical studies to elucidate the possible underlying mechanism. Some anti-hyperglycemic agents and traditional Chinese medicine may partly exert hypoglycemic effects by altering the gut microbiota composition in ways that reduce metabolic endotoxemia, maintain the integrity of intestinal mucosal barrier, promote the production of short-chain fatty acids (SCFAs), decrease trimethylamine-N-oxide (TMAO) and regulate bile acid metabolism. In conclusion, gut microbiota may provide some new therapeutic targets for treatment of patients with diabetes mellitus.

Multi-organ Coordination of Lipoprotein Secretion by Hormones, Nutrients and Neural Networks

Plasma triglyceride-rich lipoproteins (TRL), particularly atherogenic remnant lipoproteins, contribute to atherosclerotic cardiovascular disease. Hypertriglyceridemia may arise in part from hypersecretion of TRLs by the liver and intestine. Here we focus on the complex network of hormonal, nutritional, and neuronal interorgan communication that regulates secretion of TRLs and provide our perspective on the relative importance of these factors. Hormones and peptides originating from the pancreas (insulin, glucagon), gut [glucagon-like peptide 1 (GLP-1) and 2 (GLP-2), ghrelin, cholecystokinin (CCK), peptide YY], adipose tissue (leptin, adiponectin) and brain (GLP-1) modulate TRL secretion by receptor-mediated responses and indirectly via neural networks. In addition, the gut microbiome and bile acids influence lipoprotein secretion in humans and animal models. Several nutritional factors modulate hepatic lipoprotein secretion through effects on the central nervous system. Vagal afferent signaling from the gut to the brain and efferent signals from the brain to the liver and gut are modulated by hormonal and nutritional factors to influence TRL secretion. Some of these factors have been extensively studied and shown to have robust regulatory effects whereas others are "emerging" regulators, whose significance remains to be determined. The quantitative importance of these factors relative to one another and relative to the key regulatory role of lipid availability remains largely unknown. Our understanding of the complex interorgan regulation of TRL secretion is rapidly evolving to appreciate the extensive hormonal, nutritional, and neural signals emanating not only from gut and liver but also from the brain, pancreas, and adipose tissue.

GLP-1 (Glucagon-Like Peptide-1) Is Physiologically Relevant for Chylomicron Secretion Beyond Its Known Pharmacological Role

[Figure: see text].

Improvement of Postprandial Lipid Metabolism After Ileal Transposition in Non-obese Diabetic Rats

BACKGROUND

Ileal transposition (IT) could reduce obesity and improve type 2 diabetes mellitus (T2DM). The main aim of our study was to investigate lipid metabolism changes in T2DM rats after IT without a weight reduction effect.

METHODS

Thirty male diabetic rats were randomly divided into IT, sham IT (SI), and control groups. The levels of plasma cholesterol, high-density lipoprotein (HDL), low-density lipoprotein (LDL), triglycerides (TGs), and bile acid were measured. After sacrifice, the white adipose tissue, brown adipose tissue and liver were weighed.

RESULTS

IT induced significant improvement in glucose and lipid metabolism. There were no significant differences in the levels of cholesterol (P = 0.87), HDL (P = 0.70), LDL (P = 0.96), or TGs (P = 0.97) among the groups before surgery. After IT, the levels of cholesterol (P = 0.019), LDL (P = 0.004), and TGs (P < 0.001) were lower than those in the SI and control groups, while the level of HDL was not significantly different compared to those of the other groups (P = 0.437). Higher bile acid level (P = 0.001), lower white adipose tissue/total body weight ratio (P < 0.001), and lower liver/total body weight ratio (P = 0.003) were found in the IT group. The BAT/total body weight ratio in the IT group was higher than that in the SI or control groups (P = 0.002).

CONCLUSIONS

IT could improve lipid metabolism in diabetic rats.

Acute Effects of Metformin and Vildagliptin after a Lipid-Rich Meal on Postprandial Microvascular Reactivity in Patients with Type 2 Diabetes and Obesity: A Randomized Trial

Background: Type 2 diabetes mellitus and obesity are both related to endothelial dysfunction. Postprandial lipemia is a cardiovascular risk. Notably, it is known that a high-fat diet may elicit microvascular dysfunction, even in healthy subjects. Since anti-diabetic drugs have different mechanisms of action and also distinct vascular benefits, we aimed to compare the results of two anti-diabetic drugs after the intake of a lipid-rich meal on microcirculation in patients with type 2 diabetes and obesity. In parallel, we also investigated the metabolic profile, oxidative stress, inflammation, plasma viscosity, and some gastrointestinal peptides. Subjects/Methods: We included 38 drug-naïve patients, all women aged between 19 and 50 years, with BMI ≥ 30 kg/m². We performed endothelial measurements and collected samples before (fasting) and after the intake of a lipid-rich meal at 30, 60, 120, and 180 min. Patients were randomized to metformin or vildagliptin, given orally just before the meal. Endothelial function was assessed by videocapillaroscopy and laser-Doppler flowmetry to investigate microvascular reactivity. Besides, we also investigated plasma viscosity, inflammatory and oxidative stress biomarkers, gastrointestinal peptides, and metabolic profile in all time points. Results: No differences at baseline were noted between groups. Vildagliptin increased glucagon-like peptide-1 compared to metformin. Paired comparisons showed that, during the postprandial period, vildagliptin significantly changed levels of insulin and glucagon-like peptide-1, and also the dipeptidyl peptidase-4 activity, while metformin had effects on plasma glucose solely. Metformin use during the test meal promoted an increase in functional capillary density, while vildagliptin kept non-nutritive microvascular blood flow and vasomotion unchanged. Conclusions: After the intake of a lipid-rich meal, the use of vildagliptin preserved postprandial non-nutritive microflow and vasomotion, while metformin increased capillary recruitment, suggesting protective and different mechanisms of action on microcirculation.

Enteroendocrine Hormone Secretion and Metabolic Control: Importance of the Region of the Gut Stimulation

It is now widely appreciated that gastrointestinal function is central to the regulation of metabolic homeostasis. Following meal ingestion, the delivery of nutrients from the stomach into the small intestine (i.e., gastric emptying) is tightly controlled to optimise their subsequent digestion and absorption. The complex interaction of intraluminal nutrients (and other bioactive compounds, such as bile acids) with the small and large intestine induces the release of an array of gastrointestinal hormones from specialised enteroendocrine cells (EECs) distributed in various regions of the gut, which in turn to regulate gastric emptying, appetite and postprandial glucose metabolism. Stimulation of gastrointestinal hormone secretion, therefore, represents a promising strategy for the management of metabolic disorders, particularly obesity and type 2 diabetes mellitus (T2DM). That EECs are distributed distinctively between the proximal and distal gut suggests that the region of the gut exposed to intraluminal stimuli is of major relevance to the secretion profile of gastrointestinal hormones and associated metabolic responses. This review discusses the process of intestinal digestion and absorption and their impacts on the release of gastrointestinal hormones and the regulation of postprandial metabolism, with an emphasis on the differences between the proximal and distal gut, and implications for the management of obesity and T2DM.

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.

Treatment of Obesity in Mitigating Metabolic Risk

Through diverse mechanisms, obesity contributes to worsened cardiometabolic health and increases rates of cardiovascular events. Effective treatment of obesity is necessary to reduce the associated burdens of diabetes mellitus, cardiovascular disease, and death. Despite increasing cardiovascular outcome data on obesity interventions, only a small fraction of the population with obesity are optimally treated. This is a primary impetus for this article in which we describe the typical weight loss, as well as the associated impact on both traditional and novel cardiovascular disease risk factors, provided by the 4 primary modalities for obtaining weight loss in obesity-dietary modification, increasing physical activity, pharmacotherapy, and surgery. We also attempt to highlight instances where changes in metabolic risk are relatively specific to particular interventions and appear at least somewhat independent of weight loss. Finally, we suggest important areas for further research to reduce and prevent adverse cardiovascular consequences due to obesity.

Effects of underfeeding and oral vancomycin on gut microbiome and nutrient absorption in humans

Direct evidence in humans for the impact of the microbiome on nutrient absorption is lacking. We conducted an extended inpatient study using two interventions that we hypothesized would alter the gut microbiome and nutrient absorption. In each, stool calorie loss, a direct proxy of nutrient absorption, was measured. The first phase was a randomized cross-over dietary intervention in which all participants underwent in random order 3 d of over- and underfeeding. The second was a randomized, double-blind, placebo-controlled pharmacologic intervention using oral vancomycin or matching placebo (NCT02037295). Twenty-seven volunteers (17 men and 10 women, age 35.1 ± 7.3, BMI 32.3 ± 8.0), who were healthy other than having impaired glucose tolerance and obesity, were enrolled and 25 completed the entire trial. The primary endpoints were the effects of dietary and pharmacological intervention on stool calorie loss. We hypothesized that stool calories expressed as percentage of caloric intake would increase with underfeeding compared with overfeeding and increase during oral vancomycin treatment. Both primary endpoints were met. Greater stool calorie loss was observed during underfeeding relative to overfeeding and during vancomycin treatment compared with placebo. Key secondary endpoints were to evaluate the changes in gut microbial community structure as evidenced by amplicon sequencing and metagenomics. We observed only a modest perturbation of gut microbial community structure with under- versus overfeeding but a more widespread change in community structure with reduced diversity with oral vancomycin. Increase in Akkermansia muciniphila was common to both interventions that resulted in greater stool calorie loss. These results indicate that nutrient absorption is sensitive to environmental perturbations and support the translational relevance of preclinical models demonstrating a possible causal role for the gut microbiome in dietary energy harvest.

Enteroendocrine Regulation of Nutrient Absorption

Enteroendocrine cells (EECs) in the intestine regulate many aspects of whole-body physiology and metabolism. EECs sense luminal and circulating nutrients and respond by secreting hormones that act on multiple organs and organ systems, such as the brain, gallbladder, and pancreas, to control satiety, digestion, and glucose homeostasis. In addition, EECs act locally, on enteric neurons, endothelial cells, and the gastrointestinal epithelium, to facilitate digestion and absorption of nutrients. Many recent reports raise the possibility that EECs and the enteric nervous system may coordinate to regulate gastrointestinal functions. Loss of all EECs results in chronic malabsorptive diarrhea, placing EECs in a central role regulating nutrient absorption in the gut. Because there is increasing evidence that EECs can directly modulate the efficiency of nutrient absorption, it is possible that EECs are master regulators of a feed-forward loop connecting appetite, digestion, metabolism, and abnormally augmented nutrient absorption that perpetuates metabolic disease. This review focuses on the roles that specific EEC hormones play on glucose, peptide, and lipid absorption within the intestine.

The Role of the Gut Microbiota in Lipid and Lipoprotein Metabolism

Both environmental and genetic factors contribute to relative species abundance and metabolic characteristics of the intestinal microbiota. The intestinal microbiota and accompanying microbial metabolites differ substantially in those who are obese or have other metabolic disorders. Accumulating evidence from germ-free mice and antibiotic-treated animal models suggests that altered intestinal gut microbiota contributes significantly to metabolic disorders involving impaired glucose and lipid metabolism. This review will summarize recent findings on potential mechanisms by which the microbiota affects intestinal lipid and lipoprotein metabolism including microbiota dependent changes in bile acid metabolism which affects bile acid signaling by bile acid receptors FXR and TGR5. Microbiota changes also involve altered short chain fatty acid signaling and influence enteroendocrine cell function including GLP-1/GLP-2-producing L-cells which regulate postprandial lipid metabolism.

Metabolic control via nutrient-sensing mechanisms: role of taste receptors and the gut-brain neuroendocrine axis

Nutrient sensing plays an important role in ensuring that appropriate digestive or hormonal responses are elicited following the ingestion of fuel substrates. Mechanisms of nutrient sensing in the oral cavity have been fairly well characterized and involve lingual taste receptors. These include heterodimers of G protein-coupled receptors (GPCRs) of the taste receptor type 1 (T1R) family for sensing sweet (T1R2-T1R3) and umami (T1R1-T1R3) stimuli, the T2R family for sensing bitter stimuli, and ion channels for conferring sour and salty tastes. In recent years, several studies have revealed the existence of additional nutrient-sensing mechanisms along the gastrointestinal tract. Glucose sensing is achieved by the T1R2-T1R3 heterodimer on enteroendocrine cells, which plays a role in triggering the secretion of incretin hormones for improved glycemic and lipemic control. Protein hydrolysates are detected by Ca²⁺-sensing receptor, the T1R1-T1R3 heterodimer, and G protein-coupled receptor 92/93 (GPR92/93), which leads to the release of the gut-derived satiety factor cholecystokinin. Furthermore, several GPCRs have been implicated in fatty acid sensing: GPR40 and GPR120 respond to medium- and long-chain fatty acids, GPR41 and GPR43 to short-chain fatty acids, and GPR119 to endogenous lipid derivatives. Aside from the recognition of fuel substrates, both the oral cavity and the gastrointestinal tract also possess T2R-mediated mechanisms of recognizing nonnutrients such as environmental contaminants, bacterial toxins, and secondary plant metabolites that evoke a bitter taste. These gastrointestinal sensing mechanisms result in the transmission of neuronal signals to the brain through the release of gastrointestinal hormones that act on vagal and enteric afferents to modulate the physiological response to nutrients, particularly satiety and energy homeostasis. Modulating these orally accessible nutrient-sensing pathways using particular foods, dietary supplements, or pharmaceutical compounds may have therapeutic potential for treating obesity and metabolic diseases.

Conceptualization of a Parasympathetic Endocrine System

We here propose a parasympathetic endocrine system (PES) comprised of circulating peptides released from secretory cells in the gut, significantly modulated by vagal projections from the dorsal motor nucleus of the vagus (DMV). While most of these gut peptides mediate well-described satiety and digestive effects that increase parasympathetic control of digestion (Lee et al., 1994; Gutzwiller et al., 1999; Klok et al., 2007), they also have actions that are far-reaching and increase parasympathetic signaling broadly throughout the body. The actions beyond satiety that peptides like somatostatin, cholecystokinin, glucagon-like peptide 1, and vasoactive intestinal peptide have been well-examined, but not in a systematic way. Consideration has been given to the idea that these and other gut-derived peptides are part of an endocrine system has been partially considered (Rehfeld, 2012; Drucker, 2016), but that it is coordinated through parasympathetic control and may act to increase the actions of parasympathetic projections has not been formalized before. Here only gut-derived hormones are included although there are potentially other parasympathetically mediated factors released from other sites like lung and liver (Drucker, 2016). The case for the existence of the PES with the DMV as its integrative controller will be made through examination of an anatomical substrate and evidence of physiological control mechanisms as well as direct examples of PES antagonism of sympathetic signaling in mammals, including humans. The implications for this conceptual understanding of a PES reframe diseases like metabolic syndrome and may help underscore the role of the autonomic nervous system in the associated symptoms.

Incretin Hormones: The Link between Glycemic Index and Cardiometabolic Diseases

This review aimed to describe the potential mechanisms by which incretin hormones could mediate the relationship between glycemic index and cardiometabolic diseases. A body of evidence from many studies suggests that low glycemic index (GI) diets reduces the risk for type 2 diabetes and coronary heart disease. In fact, despite the extensive literature on this topic, the mechanisms underlying unfavorable effects of high GI foods on health remain not well defined. The postprandial and hormonal milieu could play a key role in the relationship between GI and cardiovascular risk. Incretin hormones, glucagon-like peptide1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP), are important regulators of postprandial homeostasis by amplifying insulin secretory responses. Response of GIP and GLP-1 to GI have been studied more in depth, also by several studies on isomaltulose, which have been taken as an ideal model to investigate the kinetics of incretin secretion in response to foods’ GI. In addition, extrapancreatic effects of these incretin hormones were also recently observed. Emerging from this have been exciting effects on several targets, such as body weight regulation, lipid metabolism, white adipose tissue, cardiovascular system, kidney, and liver, which may importantly affect the health status.

Role of Bile Acids and GLP-1 in Mediating the Metabolic Improvements of Bariatric Surgery

BACKGROUND & AIMS

Bile diversion to the ileum (GB-IL) has strikingly similar metabolic and satiating effects to Roux-en-Y gastric bypass (RYGB) in rodent obesity models. The metabolic benefits of these procedures are thought to be mediated by increased bile acids, although parallel changes in body weight and other confounding variables limit this interpretation.

METHODS

Global G protein-coupled bile acid receptor-1 null (Tgr5^-/-) and intestinal-specific farnesoid X receptor null (Fxr^Δ/E) mice on high-fat diet as well as wild-type C57BL/6 and glucagon-like polypeptide 1 receptor deficient (Glp-1r^-/-) mice on chow diet were characterized following GB-IL.

RESULTS

GB-IL induced weight loss and improved oral glucose tolerance in Tgr5^-/-, but not Fxr^Δ/E mice fed a high-fat diet, suggesting a role for intestinal Fxr. GB-IL in wild-type, chow-fed mice prompted weight-independent improvements in glycemia and glucose tolerance secondary to augmented insulin responsiveness. Improvements were concomitant with increased levels of lymphatic GLP-1 in the fasted state and increased levels of intestinal Akkermansia muciniphila. Improvements in fasting glycemia after GB-IL were mitigated with exendin-9, a GLP-1 receptor antagonist, or cholestyramine, a bile acid sequestrant. The glucoregulatory effects of GB-IL were lost in whole-body Glp-1r^-/- mice.

CONCLUSIONS

Bile diversion to the ileum improves glucose homeostasis via an intestinal Fxr-Glp-1 axis. Altered intestinal bile acid availability, independent of weight loss, and intestinal Akkermansia muciniphila appear to mediate the metabolic changes observed after bariatric surgery and might be manipulated for treatment of obesity and diabetes.

Is there a Chance to Promote Arteriogenesis by DPP4 Inhibitors Even in Type 2 Diabetes? A Critical Review

Cardiovascular diseases (CVD) are still the prevailing cause of death not only in industrialized countries, but even worldwide. Type 2 diabetes mellitus (type 2 DM) and hyperlipidemia, a metabolic disorder that is often associated with diabetes, are major risk factors for developing CVD. Recently, clinical trials proved the safety of gliptins in treating patients with type 2 DM. Gliptins are dipeptidyl-peptidase 4 (DPP4/CD26) inhibitors, which stabilize glucagon-like peptide-1 (GLP-1), thereby increasing the bioavailability of insulin. Moreover, blocking DPP4 results in increased levels of stromal cell derived factor 1 (SDF-1). SDF-1 has been shown in pre-clinical animal studies to improve heart function and survival after myocardial infarction, and to promote arteriogenesis, the growth of natural bypasses, compensating for the function of an occluded artery. Clinical trials, however, failed to demonstrate a superiority of gliptins compared to placebo treated type 2 DM patients in terms of cardiovascular (CV) outcomes. This review highlights the function of DPP4 inhibitors in type 2 DM, and in treating cardiovascular diseases, with special emphasis on arteriogenesis. It critically addresses the potency of currently available gliptins and gives rise to hope by pointing out the most relevant questions that need to be resolved.

Oral formulation of DPP-4 inhibitor plus Quercetin improves metabolic homeostasis in type 1 diabetic rats

This study aimed to investigate the potential of an oral formulation (QV formulation) containing Quercetin and a Dipeptidyl Peptidase-4 Inhibitor (DPP-4 inhibitor), Vildagliptin, in improving metabolic homeostasis in type 1 diabetes model. Female albino Fischer rats were divided into four groups: untreated control animals (C), untreated diabetic animals (D), diabetic animals treated with QV formulation (DQV), and diabetic animals treated with insulin (DI). Diabetes was induced by injection of alloxan (135 mg kg body mass)^-1 and confirmed by glycemic test. After the 30-day treatment period, biochemical parameters were analyzed in the pancreas, liver, and serum. Histopathological changes in pancreatic tissue were examined by Hematoxyline & Eosin staining and the insulin content in the islet measured by immunohistochemistry with anti-insulin antibody. The glycogen content in the hepatocytes was quantified by Periodic Schiff Acid staining. The QV formulation reduced the glycemia, preserved the pancreatic architecture, increased insulin levels, furthermore ameliorated lipid profile and to promote higher survival rate of animals. Together, our data suggest that the QV formulation treatment was able to normalize metabolic homeostasis in type 1 diabetic rats.

Dipeptidyl peptidase 4 inhibitor anagliptin ameliorates hypercholesterolemia in hypercholesterolemic mice through inhibition of intestinal cholesterol transport

Aims/Introduction

Recent data showed that dipeptidyl peptidase 4 (DPP‐4) inhibitors exert a lipid‐lowering effect in diabetes patients. However, the mechanism of action is not yet clearly understood. We investigated the effect of anagliptin on cholesterol metabolism and transport in the small intestine using non‐diabetic hyperlipidemic animals, to clarify the mechanisms underlying the cholesterol‐lowering action.

Materials and Methods

Male apolipoprotein E (ApoE)‐deficient mice were orally administered anagliptin in the normal chow. Serum cholesterol levels and lipoprotein profiles were measured, and cholesterol transport was assessed by measuring the radioactivity in the tissues after oral loading of ¹⁴C‐labeled cholesterol (¹⁴C‐Chol). In additional experiments, effects of exendin‐4 in mice and of anagliptin in DPP‐4‐deficient rats were assessed. Effects on target gene expressions in the intestine were analyzed by quantitative polymerase chain reaction in normal mice.

Results

The serum total and non‐high‐density lipoprotein cholesterol concentrations decreased after anagliptin treatment in the ApoE‐deficient mice. The cholesterol‐lowering effect was predominantly observed in the chylomicron fraction. The plasma ¹⁴C‐Chol radioactivity was significantly decreased by 26% at 2 h after cholesterol loading, and the fecal ¹⁴C‐Chol excretion was significantly increased by 38% at 72 h. The aforementioned effects on cholesterol transport were abrogated in rats lacking DPP‐4 activity, and exendin‐4 had no effect on the ¹⁴C‐Chol transport in ApoE‐deficient mice. Furthermore, significant decreases of the intestinal cholesterol transport‐related microsomal triglyceride transfer protein, acyl‐coenzyme A:cholesterol acyltransferase 2, ApoA2 and ApoC2 messenger ribonucleic acid expressions were observed in the mice treated with repeated doses of anagliptin.

Conclusions

These findings suggest that anagliptin might exert a cholesterol‐lowering action through DPP‐4‐dependent and glucagon‐like peptide 1‐independent suppression of intestinal cholesterol transport.

Regulation of intestinal lipid and lipoprotein metabolism by the proglucagon-derived peptides glucagon like peptide 1 and glucagon like peptide 2

PURPOSE OF REVIEW

The intestine is highly efficient at absorbing and packaging dietary lipids onto the structural protein apoB48 for distribution throughout the body. Here, we summarize recent advances into understanding the physiological and pharmacological actions of the proglucagon-derived peptides: glucagon like peptide 1 (GLP-1) and glucagon like peptide 2 (GLP-2) on intestinal lipoprotein secretion.

RECENT FINDINGS

Several recent studies have elucidated mechanisms underlying the paradoxical effects of GLP-1 and GLP-2 on intestinal production of triglyceride-rich lipoproteins (TRLs). Both gut-derived peptides are secreted on an equimolar basis in response to the same nutrient stimulus. Despite neither receptor demonstrating clear localization to enterocytes, a single injection of a GLP-1R agonist rapidly decreases delivery of intestinally packaged fatty acids into the plasma, while conversely GLP-2 receptor (GLP-2R) activation acutely increases TRL concentrations in plasma.

SUMMARY

The regulation of TRL secretion is dependent on the coordination of many processes: fatty acid availability uptake, assembly onto the apoB48 polypeptide backbone, secretion and reuptake, which the hormonal, neural, inflammatory and metabolic milieu can all strongly influence. Understanding of how GLP-1 and GLP-2 receptor agonists control TRL production has clinical importance given that GLP1R agonists were recently demonstrated not only to provide glycemic control but also to prevent major adverse cardiovascular events in patients with T2DM and the success of GLP-2R agonists in treating short bowel disease.

Incretin hormones: Their role in health and disease

Incretin hormones are gut peptides that are secreted after nutrient intake and stimulate insulin secretion together with hyperglycaemia. GIP (glucose-dependent insulinotropic polypeptide) und GLP-1 (glucagon-like peptide-1) are the known incretin hormones from the upper (GIP, K cells) and lower (GLP-1, L cells) gut. Together, they are responsible for the incretin effect: a two- to three-fold higher insulin secretory response to oral as compared to intravenous glucose administration. In subjects with type 2 diabetes, this incretin effect is diminished or no longer present. This is the consequence of a substantially reduced effectiveness of GIP on the diabetic endocrine pancreas, and of the negligible physiological role of GLP-1 in mediating the incretin effect even in healthy subjects. However, the insulinotropic and glucagonostatic effects of GLP-1 are preserved in subjects with type 2 diabetes to the degree that pharmacological stimulation of GLP-1 receptors significantly reduces plasma glucose and improves glycaemic control. Thus, it has become a parent compound of incretin-based glucose-lowering medications (GLP-1 receptor agonists and inhibitors of dipeptidyl peptidase-4 or DPP-4). GLP-1, in addition, has multiple effects on various organ systems. Most relevant are a reduction in appetite and food intake, leading to weight loss in the long term. Since GLP-1 secretion from the gut seems to be impaired in obese subjects, this may even indicate a role in the pathophysiology of obesity. Along these lines, an increased secretion of GLP-1 induced by delivering nutrients to lower parts of the small intestines (rich in L cells) may be one factor (among others like peptide YY) explaining weight loss and improvements in glycaemic control after bariatric surgery (e.g., Roux-en-Y gastric bypass). GIP and GLP-1, originally characterized as incretin hormones, have additional effects in adipose cells, bone, and the cardiovascular system. Especially, the latter have received attention based on recent findings that GLP-1 receptor agonists such as liraglutide reduce cardiovascular events and prolong life in high-risk patients with type 2 diabetes. Thus, incretin hormones have an important role physiologically, namely they are involved in the pathophysiology of obesity and type 2 diabetes, and they have therapeutic potential that can be traced to well-characterized physiological effects.

Effects of a Dipeptidyl Peptidase 4 Inhibitor Sitagliptin on Glycemic Control and Lipoprotein Metabolism in Patients with Type 2 Diabetes Mellitus (GLORIA Trial)

Aim: The morbidity of cardiovascular disease in patients with type 2 diabetes mellitus (DM) deteriorates in combination with dyslipidemia. The accumulation of remnant lipoproteins in patients with fasting and postprandial hypertriglyceridemia is highly atherogenic. The current study investigated whether the dipeptidyl peptidase-4 inhibitor sitagliptin ameliorates dyslipidemia and hyperglycemia.

Methods: We enrolled 38 patients with type 2 DM (20 males and 18 females, 65.7 ± 9.9 years old, HbA1c levels < 8.4%), and all patients gave written informed consent. Sitagliptin (50 mg/day) was added to current antidiabetic treatments and increased to 100 mg/day to achieve low HbA1c levels (< 7.4%). Glucose and lipoprotein metabolism profiles were analyzed at 0, 4, and 12 weeks after sitagliptin administration.

Results: Sitagliptin significantly decreased fasting levels of triglyceride (TG) (161 ± 90 vs. 130 ± 66 mg/dl, p < 0.01) and non-HDL-C (129 ± 29 vs. 116 ± 20 mg/dl, p < 0.01) in combination with glucose (150 ± 47 vs. 129 ± 27 mg/dl, p < 0.01) and HbA1c (7.1 ± 0.6 vs. 6.6 ± 0.7 mg/dl, p < 0.001). Sitagliptin also significantly decreased the fasting levels of apolipoprotein (apo) B-48 (7.8 ± 6.7 vs. 5.6 ± 4.0 µg/ml, p < 0.01), remnant lipoprotein cholesterol (15.3 ± 9.5 vs. 12.0 ± 7.9 mg/dl, p < 0.05) and other apolipoproteins, such as apoB, apoC-II, apoC-III, and apoE. Analyses of the lipoprotein profiles of fasting sera revealed that sitagliptin significantly decreased cholesterol and TG levels of lipoprotein fractions in the size of very low density lipoprotein and low density lipoprotein.

Conclusions: These findings indicated that sitagliptin administration ameliorated the lipid and lipoprotein profiles in patients with diabetes, which may be due to the decrease in atherogenic remnant lipoproteins (UMIN#000013218).

Abbreviations:apo

apolipoprotein

ASCVD

atherosclerotic cardiovascular disease

CHD

coronary heart disease

CLEIA

chemiluminescence enzyme immunoassay

CM

Chylomicron

DPP-4

dipeptidyl peptidase-4

FFAs

free fatty acids

HPLC

high-performance liquid chromatography

IMT

intima-media thickness

LDL

low-density lipoprotein

LPL

lipoprotein lipase

PHTG

postprandial hypertriglyceridemia

RemL-C

remnant lipoprotein cholesterol

RLP-C

remnant-like particle cholesterol

TG

triglyceride

TRL

triglyceride-rich lipoprotein

VLDL

very low density lipoprotein

Glucagon-like peptide-1 receptor agonists reduced the low-density lipoprotein cholesterol in Japanese patients with type 2 diabetes mellitus treated with statins

BACKGROUND

Patients with type 2 diabetes mellitus (T2DM) often have hypercholesterolemia, and their serum low-density lipoprotein cholesterol (LDL-C) levels are not always well-controlled even by statin treatment. The glucose-lowering glucagon-like peptide-1 receptor agonists (GLP-1RAs) are reported to change the lipid profiles in T2DM patients, but their effects have been unclear.

OBJECTIVE

We examined whether GLP-1RAs affect serum cholesterol levels in T2DM patients with/without statin treatment.

METHODS

We retrospectively assessed the baseline and follow-up (median 119 days) levels of serum lipids, HbA1c, and body mass index (BMI) in 103 and 214 Japanese patients with T2DM in whom GLP-1RAs were initiated (GLP-1RA group) and not initiated (control group), stratified by the use of statins.

RESULTS

In the GLP-1RA group, the LDL-C, HbA1c, and BMI significantly decreased; high-density lipoprotein cholesterol and triglycerides did not decrease during follow-up. In the control group, these did not decrease. Among the statin users, the percentage change in LDL-C during follow-up was significantly greater in the GLP-1RA group than that in the control group (-6.5% vs -1.0%, P = .040). In the GLP-1RA group, the percentage reduction in LDL-C was not associated with that in BMI but was associated with that in HbA1c only among the statin users.

CONCLUSIONS

Our findings demonstrated that GLP-1RAs reduced the serum LDL-C in Japanese patients with T2DM treated with statins. The percentage reduction in LDL-C by GLP-1RAs was associated with that in HbA1c, but not associated with that in BMI. The combination of GLP-1RAs and statins may be a reasonable therapeutic option in T2DM with dyslipidemia.

Treatment with liraglutide may improve markers of CVD reflected by reduced levels of apoB

Background

Dislipidaemia and increased levels of apolipoprotein B (apoB) in individuals with obesity are risk factors for development of cardiovascular disease (CVD). The aim of this study was to investigate the effect of weight loss and weight maintenance with and without liraglutide treatment on plasma lipid profiles and apoB.

Methods

Fifty‐eight individuals with obesity (body mass index 34.5 ± 3.0 kg/m² [mean ± SD]) were included in this study. After 8 weeks on a very low‐calorie diet (800 kcal/day), participants were randomized to weight maintenance with meal replacements with or without liraglutide (1.2 mg daily) for 1 year. Plasma samples from before and after weight loss and after 1 year of weight maintenance were subjected to nuclear magnetic resonance‐based lipidomics analysis.

Results

After an 8‐week low‐calorie diet, study participants lost 12.0 ± 2.9 kg (mean ± SD) of their body weight, which was reflected in their lipid profiles (80 out of 124 lipids changed significantly), including reduced levels of apoB, total cholesterol, free cholesterol, remnant cholesterol, triglycerides, low‐density lipoprotein and very low‐density lipoprotein subclasses. After 1 year of maintained weight loss, the majority of the lipids had returned to pre‐weight loss levels even though weight loss was successfully maintained in both groups. Interestingly, apoB levels remained low in the liraglutide treated group (apoB change: 0.03 ± 0.02 mmol/L, p = 0.4) in contrast to an increase in the control group (apoB change: 0.06 ± 0.07 mmol/L, p = 0.02).

Conclusion

An 8‐week low‐calorie diet, in individuals with obesity, reduced plasma levels of lipids and the atherogenic marker apoB. After 1 year of weight maintenance, only study participants treated with liraglutide maintained reduced levels of apoB, despite similar body weight maintenance. Treatment with liraglutide may therefore reduce apoB levels and thus reflect lower CVD risk. Including apoB measurements in clinical practice when monitoring patients with dislipidemia or CVD might prove to be useful.

Effects of GW002, a novel recombinant human glucagon-like peptide-1 (GLP-1) analog fusion protein, on CHO recombinant cells and BKS-db mice

AIMS

GLP-1-based strategies have many advantages in treatment of type 2 diabetes mellitus (T2DM), but native GLP-1 has a short half-life in the circulation, which limits its clinical application. The purpose of this study was to evaluate the effects of GW002, a novel recombinant GLP-1 analog fusion protein produced by linking the human GLP-1 analog C-terminus to the N-terminus of human serum albumin via a linker, in vitro and in BKS-db mice.

METHODS

To determine whether GW002 can activate the GLP-1 receptor in cells, the level of luciferase expression was evaluated in vitro. In vivo, body weight, food intake, non-fasting and fasting blood glucose, oral glucose tolerance test, blood glucose and insulin levels, liver histology, liver function parameters and antibody levels in BKS-db mice were investigated to evaluate the effects of GW002. Albiglutide was chosen as a positive comparator.

RESULTS

Cyclic adenosine monophosphate levels were increased in a dose-dependent manner in cells. In vivo studies demonstrated that GW002 lowers non-fasting and fasting blood glucose levels and improves glucose tolerance and insulin secretion in BKS-db mice. The degree of hepatic steatosis and hepatic biochemical indexes was also decreased. In this study, the mice body weight was not reduced significantly.

CONCLUSIONS

The above results showed that the efficacy of GW002 in BKS-db mice displayed a significant hypoglycemic effect, which indicated that GW002 might be a potential candidate for the treatment of T2DM.

Inhibition of plaque progression and promotion of plaque stability by glucagon-like peptide-1 receptor agonist: Serial in vivo findings from iMap-IVUS in Watanabe heritable hyperlipidemic rabbits

BACKGROUND AND AIMS

Glucagon-like peptide-1 (GLP-1) is thought to inhibit development of aortic atherosclerosis and plaque formation. However, whether GLP-1 stabilizes fully developed atherosclerotic plaque or alters the complicated plaque composition remains unclarified.

METHODS

Ten Watanabe heritable hyperlipidemic (WHHL) rabbits were divided into GLP-1 receptor agonist treatment group and control group. After confirmation of atherosclerotic plaques in brachiocephalic arteries by iMap intravascular ultrasound (iMAP-IVUS), GLP-1 receptor agonist lixisenatide was administered to WHHL rabbits at 30 nmoL/kg/day for 12 weeks by osmotic pump. An equal volume of normal saline was administered in a control group. After evaluation by iMAP-IVUS at 12 weeks, brachiocephalic arteries were harvested for pathological histological analysis.

RESULTS

iMAP-IVUS analysis revealed larger fibrotic plaque components and smaller necrotic and calcified plaque components in the GLP-1 group than in the control group; %fibrotic area: 66.30 ± 2.06% vs. 75.14 ± 2.62%, p < 0.01, %necrotic area: 23.25 ± 1.87% vs. 16.17 ± 2.27%, p = 0.02, %calcified area: 2.15 ± 0.24% vs. 1.00 ± 0.18%, p < 0.01), indicating that GLP-1 receptor agonist might modify plaque composition and increase plaque stability. Histological analysis confirmed that GLP-1 receptor agonist treatment improved smooth muscle cell (SMC)-rich plaque with increased fibrotic content. Furthermore, plaque macrophage infiltration and calcification were significantly reduced by GLP-1 receptor agonist treatment; %SMC area: 6.93 ± 0.31% vs. 8.14 ± 0.48%, p = 0.02; %macrophage area: 9.11 ± 0.80% vs. 6.19 ± 0.85%, p < 0.01; %fibrotic area: 54.75 ± 1.63% vs. 69.60 ± 2.12%, p = 0.02; %calcified area: 3.25 ± 0.67% vs. 0.75 ± 0.15%, p = 0.02).

CONCLUSIONS

GLP-1 receptor agonist inhibited plaque progression and promoted plaque stabilization by inhibiting plaque growth and modifying plaque composition.

APD668, a G protein-coupled receptor 119 agonist improves fat tolerance and attenuates fatty liver in high-trans fat diet induced steatohepatitis model in C57BL/6 mice

G-protein coupled receptor 119 (GPR119) receptor is a rhodopsin-like, class A Gαs-coupled receptor, predominantly expressed in pancreatic islet cells and intestinal entero-endocrine cells. GPR119 has been emerged as a novel therapeutic target for the treatment of dyslipidemia in type 2 diabetes. In this study, we investigated the effect of APD668, a GPR119 agonist alone and in combination with linagliptin, a DPPIV inhibitor on oral fat tolerance test. Our findings demonstrate that APD668, a GPR119 agonist inhibits the intestinal triglyceride absorption after acute fat load in mice. Single dose administration of APD668 increases incretin secretion and enhances total PYY levels in presence of fat load in mice. We found that, the anti-dyslipidemic action of APD668 was reversed in presence of exendin-3 in oral fat tolerance test. In addition, our results showed that exendin-3 (9-39) failed to block the effect of APD668 on gastric emptying indicating that gastric emptying effects of APD668 are indeed mediated through GPR119 receptor dependent mechanism. Combined administration of APD668 and linagliptin significantly increased plasma active GLP-1 levels in-vivo and showed improvement in fat tolerance. However, APD668 failed to show anti-dyslipidemic activity in tyloxapol-induced hyperlipidemia in mice. Furthermore, we investigated the chronic effects of APD668 on hepatic steatosis in high trans-fat diet fed steatohepatitis model in mice. Oral administration of APD668 in HTF diet fed mice ameliorated hepatic endpoints such as plasma ALT, AST, liver weight and steatosis. These findings suggest that GPR119 agonists may represent a promising therapeutic strategy for the treatment of dyslipidemia and non-alcoholic steatohepatitis.

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.

Mechanisms of Cardiovascular Injury in Type 2 Diabetes and Potential Effects of Dipeptidyl Peptidase-4 Inhibition

BACKGROUND

Cardiovascular (CV) disease is the major cause of mortality and morbidity in patients with type 2 diabetes mellitus (T2DM). The pathogenesis of CV disease in T2DM is complex and multifactorial and involves direct and indirect injury to the vasculature and heart. The impact of intensive glucose-lowering therapy with antihyperglycemic agents on CV outcomes is not clear, and questions remain as to which glucose-lowering agents may be beneficial to CV health in patients with T2DM.

PURPOSE

This review discusses findings regarding the known mechanisms of CV injury in T2DM and current knowledge regarding the potential cardioprotective effects of dipeptidyl peptidase-4 (DPP-4) inhibitors.

CONCLUSIONS

Dipeptidyl peptidase-4 inhibitors are relatively new antihyperglycemic agents. Their main mechanism of action is to inhibit the degradation of the incretin hormones glucagon-like peptide-1 and glucose-dependent insulinotropic peptide by DPP-4. By increasing levels of glucagon-like peptide-1, glucose-dependent insulin secretion is enhanced, glucagon secretion is suppressed, and the rate of gastric emptying is decreased. Dipeptidyl peptidase-4 also degrades other substances that are important in the regulation of CV function and inflammation. Animal studies, small observational studies in humans, and analyses of clinical trial data suggest that DPP-4 inhibitors may have beneficial CV effects. Recent prospectively designed CV outcomes trials with saxagliptin and alogliptin in patients with T2DM and high CV risk presented evidence that these DPP-4 inhibitors neither increased nor decreased adverse CV outcomes in this select patient population.

CLINICAL IMPLICATIONS

Dipeptidyl peptidase-4 inhibitors are promising therapies for the treatment of T2DM. Able to improve glycemic control without the risk of weight gain or hypoglycemia, they provide a safe alternative to sulfonylureas and are an effective adjunct to metformin. To date, this class of drugs seems to be at least neutral in terms of CV effects. Time will tell if these findings translate into a benefit for our patients.

Vildagliptin ameliorates biochemical, metabolic and fatty changes associated with non alcoholic fatty liver disease

Objective:

To determine the effect of Vildagliptin in non-alcoholic, fatty liver disease patients with dyslipidemia.

Methods:

A randomized placebo controlled trial was conducted at outpatient clinic of Medical Unit-I of Sheikh Zayed Medical College/Hospital, Rahim Yar Khan, in which fifty eight patients of NAFLD with dyslipidemia were divided in to two, case and control groups. The case group was given tablet Vildagliptin 50mg twice a day for twelve weeks and control group was given placebo in same way. Body weight, body mass index (BMI), lipid profile, liver enzymes and ultrasound finding of fatty liver were assayed before and after treatment.

Results:

After 12 weeks treatment of vildagliptin there was significant improvement in following parameters. Body weight and BMI decreased significantly from 88 ± 11 to79 ± 12 kg (p0.036) and 30±4to 27±5 kg/m² (p 0.005) respectively. Notable reduction in the value of TC, TG and LDL-C (TC:252±24 to 220±20mg/dl (p 0.031); TG: 190±24 to115±22 mg/dl (p 0.005); LDL-C 160±15 to 145±13mg/dl (p 0.004). HDL-C level increased significantly from 29±5to45±4 mg/dl (p 0.001). There was remarkable reduction in aminotransferases level (ALT: 78± 17 to 48±14IU/L (p 0.036). AST: 63.3±13 to41±11IU/L (p 0.002). There was overall 65.5% improvement in fatty liver grading on ultrasound with vildagliptin while non significant effects were seen in placebo group in all of the above parameters.

Conclusion:

Vildagliptin exhibited beneficial effects in non-alcoholic fatty liver disease, Non-diabetic patients with dyslipidemia.

Pleiotropic effects of insulin and GLP-1 receptor agonists: Potential benefits of the association

The combination of basal insulin and glucagon-like peptide-1 receptor agonists (GLP-1RAs) is an emerging option for patients with type 2 diabetes (T2D). GLP-1RAs have been shown to improve glycaemic control with a low risk of hypoglycaemia and to promote body weight loss. However, GLP-1 receptors (GLP-1Rs) are widely expressed in extrapancreatic tissues and could sustain pleiotropic actions of GLP-1RAs beyond glycaemic control. The underlying molecular mechanisms maintaining these extrapancreatic actions of GLP-1 are complex, and involve GLP-1R signalling in both the brain and several peripheral tissues. The present review focuses specifically on the role of GLP-1RAs in the cardiovascular system and liver. Preclinical data in rodents and pilot studies in humans suggest that GLP-1RAs may have potential beneficial effects on heart function, blood pressure, postprandial lipaemia, liver steatosis and non-alcoholic steatohepatitis (NASH). Long-term studies are now warranted to determine the safety and clinical relevance of the association between insulin and GLP-1RAs in T2D.

Lessons learned from cardiovascular outcome clinical trials with dipeptidyl peptidase 4 (DPP-4) inhibitors

Previous trials of glucose-lowering strategies in subjects with type 2 diabetes have demonstrated a beneficial effect of intensive glycemic control on microvascular complications but failed to show a clear benefit on cardiovascular complications. The findings of meta-analyses of rosiglitazone trials suggesting that rosiglitazone might increase the risk of myocardial infarction have cast doubt on the cardiovascular safety of glucose-lowering drugs. In 2008, the US Food and Drug Administration has implemented rigorous criteria to approve new glucose-lowering drugs, requiring proof of cardiovascular safety. These regulatory requirements have led to a considerable increase in the number of cardiovascular outcome trials in type 2 diabetes to ensure that newer glucose-lowering drugs are not associated with increased cardiovascular risk. Incretin-based therapies including dipeptidyl peptidase 4 (DPP-4) inhibitors, and injectable glucagon-like peptide 1 (GLP-1) receptor agonists are novel treatment options for patients with inadequate glucose control. Although DPP-4 inhibitors have shown neutral effects on risk factors for cardiovascular diseases, it remains unclear whether treatment with these new glucose-lowering agents might be associated with a reduction in cardiovascular events. The results of the three cardiovascular outcome trials comparing DPP-4 inhibitors treatment to placebo in addition to other glucose-lowering drugs have been published. All the three DPP-4 inhibitor cardiovascular outcome trials have shown non-inferiority with regard to cardiovascular safety, compared with placebo, when added to usual care. In this review, we summarize cardiovascular outcome trials of DPP-4 inhibitors, and provide an overview of these trials and their limitations.

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.

Effect of treatment with sitagliptin on somatosensory-evoked potentials and metabolic control in patients with type 2 diabetes mellitus

OBJECTIVE

To evaluate the effect of sitagliptin on somatosensory-evoked potentials (SEPs) and metabolic control in patients with type 2 diabetes mellitus without clinical diabetic neuropathy.

MATERIALS AND METHODS

Interventional, prospective, and open study. Patients with less than six months from the diagnosis were included. Examinations of SEPs and laboratory tests at fasting and after food stimulation were performed before and after three months of treatment with sitagliptin (100 mg/day).

RESULTS

There was a reduction in the mean levels of HbA1c (P < 0.0001), fasting glucose (P = 0.001), total cholesterol (P = 0.019), and ALT (P = 0.022). An increase in active GLP-1 was found at the end of the study (P = 0.0025). Several SEPs showed statistically significant differences when analyzed before and after treatment with sitagliptin.

CONCLUSION

The results give a glimpse of the possible use of sitagliptin in the treatment of some neurodegenerative conditions of the peripheral nervous system, in addition to its already established role in glycemic control.

Recent Advances in Dipeptidyl-Peptidase-4 Inhibition Therapy: Lessons from the Bench and Clinical Trials

DPP4 inhibitors (DPP4i) are a class of newly developed antidiabetic drugs which preserve incretin hormones and promote postprandial insulin secretion. Although the cardiovascular effect of DPP4 inhibition has been substantially studied, the exact role of DPP4 in cardiovascular disease especially in humans remains elusive. Previous small studies and meta-analyses have suggested a benefit in both surrogate outcomes and cardiovascular events for these agents. However, there was growing evidence in recent years questioning the cardioprotective effect of DPP4i. Further, a signal of heart failure hospitalization in a recent large scale clinical trial SAVOR-TIMI 53 has called into question the safety of these agents and their utility in the treatment of cardiovascular disease. In this review, we will revisit the physiologic function of DPP4 and discuss its role in cardiometabolic disease based on recent experimental and clinical studies.

Postprandial Dysmetabolism and Oxidative Stress in Type 2 Diabetes: Pathogenetic Mechanisms and Therapeutic Strategies

Postprandial dysmetabolism in type 2 diabetes (T2D) is known to impact the progression and evolution of this complex disease process. However, the underlying pathogenetic mechanisms still require full elucidation to provide guidance for disease prevention and treatment. This review focuses on the marked redox changes and inflammatory stimuli provoked by the spike in blood glucose and lipids in T2D individuals after meals. All the causes of exacerbated postprandial oxidative stress in T2D were analyzed, also considering the consequence of enhanced inflammation on vascular damage. Based on this in-depth analysis, current strategies of prevention and pharmacologic management of T2D were critically reexamined with particular emphasis on their potential redox-related rationale.