Effects of Pioglitazone on Glucose-Dependent Insulinotropic Polypeptide-Mediated Insulin Secretion and Adipocyte Receptor Expression in Patients With Type 2 Diabetes

Novel pharmacotherapies for weight loss: Understanding the role of incretins to enable weight loss and improved health outcomes

Obesity and type 2 diabetes mellitus (T2D) are widespread diseases that significantly impact cardiovascular and renal morbidity and mortality. In the recent years, intensive research has been performed to assess the role of adipose tissue and body fat distribution in the development of metabolic and non-metabolic complications in individuals with obesity. In addition to lifestyle modifications, glucagon-like peptide-1 receptor agonists (GLP-1-RA) have become a meaningful treatment expansion for the management of both disorders. In addition to improving metabolic control and reducing body weight, treatment with GLP-1-RAs reduces cardiovascular and renal events in individuals with obesity with and without diabetes. These important benefits of GLP-1-RAs have triggered new interest in other enteroendocrine and enteropancreatic peptides for treating obesity and its metabolic and non-metabolic consequences. The first peptide dual-agonist targeting glucose-dependent insulinotropic polypeptide (GIP) and GLP-1 receptors has been approved for the treatment of T2D and obesity. GIP/GLP-1 dual-agonism appear to provide better metabolic control and greater weight reduction compared with GLP-1-R mono-agonism. Other peptide and non-peptide co-agonists are in clinical development for obesity, T2D, metabolic dysfunction-associated steatotic liver disease (MASLD) and other metabolic disorders. This narrative review aims to summarize the available data on approved and emerging enteroendocrine and enteropancreatic based treatment approaches for obesity and metabolic disorders. In addition to available clinical efficacy measures, side effects, limitations and open challenges will also be addressed.

The GIP receptor activates futile calcium cycling in white adipose tissue to increase energy expenditure and drive weight loss in mice

Obesity is a chronic disease that contributes to the development of insulin resistance, type 2 diabetes (T2D), and cardiovascular risk. Glucose-dependent insulinotropic polypeptide (GIP) receptor (GIPR) and glucagon-like peptide-1 (GLP-1) receptor (GLP-1R) co-agonism provide an improved therapeutic profile in individuals with T2D and obesity when compared with selective GLP-1R agonism. Although the metabolic benefits of GLP-1R agonism are established, whether GIPR activation impacts weight loss through peripheral mechanisms is yet to be fully defined. Here, we generated a mouse model of GIPR induction exclusively in the adipocyte. We show that GIPR induction in the fat cell protects mice from diet-induced obesity and triggers profound weight loss (∼35%) in an obese setting. Adipose GIPR further increases lipid oxidation, thermogenesis, and energy expenditure. Mechanistically, we demonstrate that GIPR induction activates SERCA-mediated futile calcium cycling in the adipocyte. GIPR activation further triggers a metabolic memory effect, which maintains weight loss after the transgene has been switched off, highlighting a unique aspect in adipocyte biology. Collectively, we present a mechanism of peripheral GIPR action in adipose tissue, which exerts beneficial metabolic effects on body weight and energy balance.

GIPR Agonism Enhances TZD-Induced Insulin Sensitivity in Obese IR Mice

Recent studies have found that glucose-dependent insulinotropic polypeptide receptor (GIPR) agonism can enhance the metabolic efficacy of glucagon-like peptide-1 receptor agonist treatment by promoting both weight-dependent and -independent improvements on systemic insulin sensitivity. These findings have prompted new investigations aimed at better understanding the broad metabolic benefit of GIPR activation. Herein, we determined whether GIPR agonism favorably influenced the pharmacologic efficacy of the insulin-sensitizing thiazolidinedione (TZD) rosiglitazone in obese insulin-resistant (IR) mice. Genetic and pharmacological approaches were used to examine the role of GIPR signaling on rosiglitazone-induced weight gain, hyperphagia, and glycemic control. RNA sequencing was conducted to uncover potential mechanisms by which GIPR activation influences energy balance and insulin sensitivity. In line with previous findings, treatment with rosiglitazone induced the mRNA expression of the GIPR in white and brown fat. However, obese GIPR-null mice dosed with rosiglitazone had equivalent weight gain to that of wild-type (WT) animals. Strikingly, chronic treatment of obese IR WT animals with a long-acting GIPR agonist prevented rosiglitazone-induced weight-gain and hyperphagia, and it enhanced the insulin-sensitivity effect of this TZD. The systemic insulin sensitization was accompanied by increased glucose disposal in brown adipose tissue, which was underlined by the recruitment of metabolic and thermogenic genes. These findings suggest that GIPR agonism can counter the negative consequences of rosiglitazone treatment on body weight and adiposity, while improving its insulin-sensitizing efficacy at the same time.

ARTICLE HIGHLIGHTS

Optimizing glycation control in diabetes: An integrated approach for inhibiting nonenzymatic glycation reactions of biological macromolecules

Diabetes is a multifactorial disorder that increases mortality and disability due to its complications. A key driver of these complications is nonenzymatic glycation, which generates advanced glycation end-products (AGEs) that impair tissue function. Therefore, effective nonenzymatic glycation prevention and control strategies are urgently needed. This review comprehensively describes the molecular mechanisms and pathological consequences of nonenzymatic glycation in diabetes and outlines various anti-glycation strategies, such as lowering plasma glucose, interfering with the glycation reaction, and degrading early and late glycation products. Diet, exercise, and hypoglycemic medications can reduce the onset of high glucose at the source. Glucose or amino acid analogs such as flavonoids, lysine and aminoguanidine competitively bind to proteins or glucose to block the initial nonenzymatic glycation reaction. In addition, deglycation enzymes such as amadoriase, fructosamine-3-kinase, parkinson's disease protein, glutamine amidotransferase-like class 1 domain-containing 3A and terminal FraB deglycase can eliminate existing nonenzymatic glycation products. These strategies involve nutritional, pharmacological, and enzymatic interventions that target different stages of nonenzymatic glycation. This review also emphasizes the therapeutic potential of anti-glycation drugs for preventing and treating diabetes complications.

GIPR expression is induced by thiazolidinediones in a PPARγ-independent manner and repressed by obesogenic stimuli

Adipose tissue (AT) dysfunctions are associated with the onset of insulin resistance (IR) and type 2 diabetes mellitus (T2DM). Targeting glucose-dependent insulinotropic peptide receptor (GIPR) is a valid option to increase the efficacy of glucagon-like peptide 1 (GLP-1) receptor agonists in T2DM treatment. Nevertheless, the therapeutic potential of targeting the GIP/GIPR axis and its effect on the AT are controversial. In this work, we explored the expression and regulation of GIPR in precursor cells and mature adipocytes, investigating if and how obesogenic stimuli and thiazolidinediones perturb GIPR expression. Using publicly available gene expression datasets, we assessed that, among white adipose tissue (WAT) cells, adipocytes express lower levels of GIPR compared to cells of mesothelial origin, pericytes, dendritic and NK/T cells. However, we report that GIPR levels markedly increase during the in vitro differentiation of both murine and human adipocytes, from 3T3-L1 and human mesenchymal precursor cells (MSCs), respectively. Notably, we demonstrated that thiazolidinediones - ie. synthetic PPARγ agonists widely used as anti-diabetic drugs and contained in the adipogenic mix - markedly induce GIPR expression. Moreover, using multiple in vitro systems, we assessed that thiazolidinediones induce GIPR in a PPARγ-independent manner. Our results support the hypothesis that PPARγ synthetic agonists may be used to increase GIPR levels in AT, potentially affecting in turn the targeting of GIP system in patients with metabolic dysfunctions. Furthermore, we demonstrate in vitro and in vivo that proinflammatory stimuli, and especially the TNFα, represses GIPR both in human and murine adipocytes, even though discordant results were obtained between human and murine cellular systems for other cytokines. Finally, we demonstrated that GIPR is negatively affected also by the excessive lipid engulfment. Overall, we report that obesogenic stimuli - ie. pro-inflammatory cytokines and the increased lipid accumulation - and PPARγ synthetic ligands oppositely modulate GIPR expression, possibly influencing the effectiveness of GIP agonists.

Effects of calcium salts of palm oil inclusion and ad libitum feeding regimen on growth performance, carcass characteristics, and plasma glucose-dependent insulinotropic polypeptide concentration of feedlot steers

Sixty Angus × SimAngus-crossbred steers (body weight [BW] 279 ± 16 kg) were used to evaluate the effect of calcium salts of palm oil inclusion (CPO) and the amount of feed offered (AFO) on plasma glucose-dependent insulinotropic polypeptide (GIP) concentration and its association with energy metabolism and marbling score (MS) in feedlot steers. Steers were blocked by BW and gain to feed (G:F) and randomly assigned to individual feedlot pens. Treatments (2 × 2 factorial) consisted of ad libitum-fed steers without (ANF) or with (AWF) the inclusion of CPO or restricted-fed steers (85% of the ad libitum intake of ANF) without (RNF) or with the inclusion of CPO (RWF). After weaning, steers were adapted to individual pens and fed a corn silage-based diet for 30 d and subsequently placed in a ground corn (GC)-based diet. Diets were given ad libitum or at 85% of the ANF intake and with or without CPO. After 59 d on the finishing diet, all steers had ad libitum access to the finishing diet until harvest. Measurements of CO2 emission and O2 consumption to estimate respiratory quotient (RQ) were taken (n = 9/treatment). Correlations between plasma GIP and insulin concentrations and RQ were analyzed. A linear regression was performed to evaluate the association of plasma GIP and MS. All data were analyzed using the PROC MIXED procedure of SAS. During the first 103 d of the trial, there were AFO × CPO interactions (P ≤ 0.01) for BW, dry matter intake (DMI), average daily gain (ADG), and net energy for maintenance (NEm) intake. Ad libitum-fed steers without CPO presented the greatest DMI among dietary treatments and had greater BW and ADG compared with steers in the RWF and RNF treatments. After all steers had ad libitum access to dietary treatments, steers that were previously restricted showed a 30% and 19% increase (P ≤ 0.01) in ADG and G:F, respectively. There was a three-way interaction time × CPO × AFO (P = 0.04) for plasma GIP concentration. There was no correlation (P = 0.96) of GIP with RQ, whereas insulin demonstrated marginal significance for a positive (P = 0.07) and negative (P = 0.08) correlation with plasma GIP and RQ, respectively. There was no association (P = 0.30) between GIP and MS. These data indicate that GIP secretion results from an interaction between CPO and energy intake depending on the time relative to feed intake that GIP might indirectly regulate energy metabolism through insulin secretion, and that GIP does not appear to be associated with MS.

Evaluation of the association between plasma glucose-dependent insulinotropic polypeptide, respiratory quotient, and intramuscular fat deposition in feedlot cattle fed different levels of dry matter intake

The objectives of this trial were to evaluate the association between different levels of dry matter intake (DMI) on gas exchange, plasma glucose-dependent insulinotropic polypeptide (GIP) concentration, and intramuscular (IM) fat deposition. We used 60 individually fed backgrounded Angus × SimAngus-crossbred steers (n = 30) in a randomized complete block design. Steers (paired by body weight [BW] and gain to feed ratio [G:F]) were randomly allocated to one of the following treatments: ad libitum intake (AI) or restricted intake (RI; the same diet fed at 85% of the AI) of a finishing diet. The diet contained 61% cracked corn, 9% corn silage, 15% distillers’ dried grains with solubles, 5% soyhulls, and 10% of a protein-mineral-vitamin premix. Measurements of CO₂ emission and consumption of O₂, and respiratory quotient (RQ) were taken using the GreenFeed system (n = 15/treatment). Plasma and gas samples were collected 10 d before slaughter, 1 h before and 2 h after feeding. Plasma glucose, non-esterified fatty acids, GIP, and insulin concentration and gasses (O_2, CO_2, and RQ) were analyzed using the MIXED procedure of SAS evaluating the fixed effect of treatment, time (repeated measurement) and their interaction, and the random effect of the block. Final BW and carcass characteristics were analyzed with a similar model, without the time statement and its interaction. Compared with RI, AI steers had greater (P < 0.01) DMI and average daily gain (ADG). Steers on AI had greater final BW (P = 0.02), tended to have a greater ribeye area (P = 0.09), and had lower plasma GIP concentration (P = 0.04). There was no treatment effect (P ≥ 0.11) on G:F, subcutaneous backfat (BF), and IM fat, O₂ consumption, CO₂ emission, and RQ. Plasma glucose concentration of AI steers was greater before and after feeding than RI (P < 0.05). In conclusion, feeding steers ad libitum increased DMI, ADG, and plasma glucose and GIP concentration but does not affect G:F, BF, IM fat, CO₂ emission, and O₂ consumption. Plasma GIP concentration and RQ are not associated with IM fat deposition.

Coordinated regulation of gene expression and microRNA changes in adipose tissue and circulating extracellular vesicles in response to pioglitazone treatment in humans with type 2 diabetes

Pioglitazone, a PPARγ agonist, is used to treat type 2 diabetes (T2D). PPARγ is highly expressed in adipose tissue (AT), however the effects of pioglitazone to improve insulin sensitivity are also evident in other tissues and PPARγ agonism has been shown to alter cancer derived extracellular vesicle (EV)-miRNAs. We hypothesized that pioglitazone modifies the cargo of circulating AT-derived EVs to alter interorgan crosstalk in people with diabetes. We tested our hypothesis in a 3-month trial in which 24 subjects with T2D were randomized to treatment with either pioglitazone 45 mg/day or placebo (NCT00656864). Levels of 42 adipocyte-derived EV-miRNAs were measured in plasma EVs using low density TaqMan arrays. Levels of differentially expressed EV-miRNAs and their most relevant target genes were also measure in adipose tissue from the same participants, using individual TaqMan assays. Levels of 5 miRNAs (i.e., miR-7-5p, miR-20a-5p, miR-92a-3p, miR-195-5p, and miR-374b-5p) were significantly downregulated in EVs in response to pioglitazone treatment relative to placebo. The opposite occurred for miR-195-5p in subcutaneous AT. Changes in miRNA expression in EVs and AT correlated with changes in suppression of lipolysis and improved insulin sensitivity, among others. DICER was downregulated and exosomal miRNA sorting-related genes YBX1 and hnRNPA2B1 displayed a downregulation trend in AT. Furthermore, analysis of EV-miRNA targeted genes identified a network of transcripts that changed in a coordinated manner in AT. Collectively, our results suggest that some beneficial pharmacologic effects of pioglitazone are mediated by adipose-specific miRNA regulation and exosomal/EV trafficking.

CLINICAL TRIAL REGISTRATION

ClinicalTrials.gov, identifier NCT00656864.

A Pharmacological and Clinical Overview of Oral Semaglutide for the Treatment of Type 2 Diabetes

Oral semaglutide (Rybelsus®) is a glucagon-like peptide-1 (GLP-1) receptor agonist (GLP-1RA) with 94% homology to human GLP-1. It is the first GLP-1RA developed for oral administration, and it comprises a co-formulation of the peptide semaglutide with the absorption enhancer sodium N-(8-[2-hydroxybenzoyl] amino) caprylate, which overcomes the challenges of peptide absorption in the acidic conditions of the stomach. Oral semaglutide is indicated for use as an add-on combination therapy (with other glucose-lowering agents, including insulin) or as a monotherapy (in patients who are intolerant to metformin) for type 2 diabetes when diet and exercise do not provide adequate glycemic control. In an extensive phase III clinical program including patients from across the disease spectrum, treatment with oral semaglutide resulted in effective glycemic control, reductions in body weight, and decreases in systolic blood pressure when used as monotherapy or in combination with other glucose-lowering therapies. Studies showed that oral semaglutide was well tolerated, with a safety profile consistent with the GLP-1RA drug class. The risk of hypoglycemia was low, and the most common adverse events were gastrointestinal, with nausea and diarrhea generally being the most frequently reported manifestations. Cardiovascular (CV) safety was shown to be noninferior to placebo and observations suggest that the CV profile of oral semaglutide is likely to be similar to that of subcutaneous semaglutide. The evolution of the GLP-1RA class to include an oral agent could facilitate the use of these agents earlier in the diabetes treatment cascade owing to wider acceptance from patients and healthcare professionals.

How May GIP Enhance the Therapeutic Efficacy of GLP-1?

Glucagon-like peptide-1 (GLP-1) receptor agonists improve glucose homeostasis, reduce bodyweight, and over time benefit cardiovascular health in type 2 diabetes mellitus (T2DM). However, dose-related gastrointestinal effects limit efficacy, and therefore agents possessing GLP-1 pharmacology that can also target alternative pathways may expand the therapeutic index. One approach is to engineer GLP-1 activity into the sequence of glucose-dependent insulinotropic polypeptide (GIP). Although the therapeutic implications of the lipogenic actions of GIP are debated, its ability to improve lipid and glucose metabolism is especially evident when paired with the anorexigenic mechanism of GLP-1. We review the complexity of GIP in regulating adipose tissue function and energy balance in the context of recent findings in T2DM showing that dual GIP/GLP-1 receptor agonist therapy produces profound weight loss, glycemic control, and lipid lowering.