Efficacy and safety of high-dose glucagon-like peptide-1, glucagon-like peptide-1/glucose-dependent insulinotropic peptide,and glucagon-like peptide-1/glucagon receptor agonists in type 2 diabetes

Glucagon-like peptide-1 receptor agonists (GLP-1 RAs) have become agents of choice for people with type 2 diabetes (T2D) with established cardiovascular disease or in high-risk individuals. With currently available GLP-1 RAs, 51%-79% of subjects achieve an HbA1c target of less than 7.0% and 4%-27% lose 10% of body weight, illustrating the need for more potent agents. Three databases (PubMed, Cochrane, Web of Science) were searched using the MESH terms ‘glucagon-like peptide-1 receptor agonist’, ‘glucagon receptor agonist’, ‘glucose-dependent insulinotropic peptide’, ‘dual or co-agonist’, and ‘tirzepatide’. Quality of papers was scored using PRISMA guidelines. Risk of bias was evaluated using the Cochrane assessment tool. An HbA1c target of less than 7.0% was attained by up to 80% with high-dose GLP-1 RAs and up to 97% with tirzepatide, with even up to 62% of people with T2D reaching an HbA1c of less than 5.7%. A body weight loss of 10% or greater was obtained by up to 50% and up to 69% with high-dose GLP-1 RAs or tirzepatide, respectively. The glucose- and weight-lowering effects of the GLP-1/glucagon RA cotadutide equal those of liraglutide 1.8 mg. Gastrointestinal side effects of high-dose GLP-1 RAs and co-agonists occurred in 30%-70% of patients, mostly arising within the first 2 weeks of the first dose, being mild or moderate in severity, and transient. The development of high-dose GLP-1 RAs and the dual GLP-1/glucose-dependent insulinotropic peptide RA tirzepatide resulted in increasing numbers of people reaching HbA1c and body weight targets, with up to 62% attaining normoglycaemia with 15-mg tirzepatide. Whether this will also translate to better cardiovascular outcomes and affect treatment guidelines remains to be studied.     

胰高血糖素样肽-1对大鼠骨骼肌细胞糖原合成的影响及其机制

目的 研究胰高血糖素样肽-1对大鼠骨骼肌细胞的影响及其机制.方法 体外培养大鼠骨骼肌细胞,采用检测细胞存活和生长的方法（MTT法）检测胰高血糖素样肽-1、胰岛素对骨骼肌细胞存活数量的影响,应用免疫组织化学法测定糖原合成酶和磷酸化糖原合成酶激酶-3α/β表达水平,Western blotting验证胰高血糖素样肽-1对磷脂酰肌醇-3-激酶通路的影响.将骨骼肌细胞分为对照组、胰高血糖素样肽-1组、LY294002组、胰高血糖素样肽-1＋LY294002组,于48和72 h分别测定糖原合成酶和磷酸化糖原合成酶激酶-3α/β的表达水平.采用单因素方差分析进行多组间均数比较.结果 Western blotting检测结果显示,胰高血糖素样肽-1刺激后15、30 min、1、2、8h,大鼠骨骼肌细胞出现明显的阳性颗粒表达.与胰高血糖素样肽-1组相比,对照组、LY294002组、胰高血糖素样肽-1＋ LY294002组磷酸化糖原合成酶激酶-3α/β表达水平明显降低（分别为0.93±0.11、0.52±0.05、0.65±0.07、0.54±0.21,t值分别为5.751、3.651、2.811,均P＜0.05）,糖原合成酶明显降低（分别为0.84±0.14、0.28±0.05、0.34±0.22、0.57±0.08,t值分别为6.390、3.260、2.801,均P＜0.05）.结论 本研究证实胰高血糖素样肽-1可通过激活大鼠骨骼肌细胞磷脂酰肌醇-3-激酶通路增加糖原合成酶活性,促进糖原合成.     

Effect of glucagon-like peptide-1 (GLP-1) analogues on epicardial adipose tissue: A meta-analysis

Background and aimsGlucagon-like peptide-1 (GLP-1) analogues reduce body fat and cardiovascular events in patients with type 2 diabetes. Accumulation of epicardial adipose tissue (EAT) is associated with increased cardio-metabolic risks and coronary events in type 2 diabetes.MethodsA systematic review and meta-analysis were performed from Glucagon-like peptide-1 analogues therapy on type 2 diabetes patients, reporting data from changes in EAT, after searching the PubMed/MEDLINE, Embase, Science Direct, Scopus, Google Scholar, and Cochrane databases.ResultsIt has been found a limited number of studies, a total of 4 studies (n = 160 patients with GLP-1 analogues therapy) were included in the final analysis. Pooled analysis revealed that GLP-1 analogues reduce EAT (MD: 1.83 mm [-2.50; ?1.10]; P < 0.01). Compared with the patients before the treatment, the patients after the treatment had a smaller HbA1c (MD -1.10%[-1.80; ?0.30]; p = 0.0143) and body mass index was reduced (MD -2.20 kg/m²[-3.70; ?0.60]; p = 0.0058), GLP-1 therapy reduced low-density lipoprotein levels (MD-13.53 mg/dL [-21.74; ?5.31]; p = 0.001) and reduced triglycerides levels significantly (MD -18.32 -28.20 mg/dL; ?8.50); p = 0.0003).ConclusionsThis meta-analysis suggests that the amount of EAT is significantly reduced in T2D patients with Glucagon-like peptide-1 analogues.     

The essential role of insulin-like growth factor-1 in the intestinal tropic effects of glucagon-like peptide-2 in mice

BACKGROUND & AIMS: Glucagon-like peptide-2 (GLP-2) is an intestinal hormone that acts through unknown pathways to induce intestinal growth. We investigated the role of the insulin-like growth factors (IGF-1 and IGF-2) as mediators of GLP-2-enhanced growth in the murine intestine. METHODS: IGF-1 expression and secretion were determined in GLP-2-responsive primary intestinal cultures treated with GLP-2. Parameters of intestinal growth were assessed in wild-type (CD1, Igf1(+/+) and Igf2+), heterozygous (Igf1(+/-)), and null (Igf1(-/-) and Igf2(-P)) mice treated chronically with saline, GLP-2, IGF-1, or R-Spondin1. RESULTS: GLP-2 increased IGF-1 messenger RNA expression and IGF-1 secretion in intestinal cultures and increased expression of IGF-1 messenger RNA in mouse small intestine in vivo. Igf1(+/+) and Igf2+ mice responded to .1 microg/g(-1) per day(-1) GLP-2 with increased intestinal weights, morphometric parameters, and proliferative indices. In contrast, Igf1(-/-) mice were unresponsive to the same dose of GLP-2, failing to demonstrate changes in intestinal weight, morphometry, or proliferation. However, a significant effect of 1 microg/g(-1) per day(-1) GLP-2 was observed in Igf1(-/-) mice, but only in terms of small intestinal weight when normalized for body weight. Furthermore, Igf2(-P) mice demonstrated a partially impaired response in terms of small intestinal growth. Both Igf1(-/-) and Igf2(-P) mice exhibited normal-enhanced intestinal growth in response to IGF-1 and/or R-Spondin1. CONCLUSIONS: GLP-2 enhances intestinal IGF-1 expression and secretion, and IGF-1 is required for small and large intestinal growth in response to GLP-2. These findings identify IGF-1 as an essential mediator of the intestinotropic actions of GLP-2.     

Mucosal adaptation to enteral nutrients is dependent on the physiologic actions of glucagon-like peptide-2 in mice

BACKGROUND & AIMS: Our understanding of the intestinotropic actions of glucagon-like peptide-2 (GLP-2)(1-33) is based on pharmacologic studies involving exogenous administration. However, the physiologic role of GLP-2 in mucosal growth and adaptation to nutritional stimulation remains poorly understood. METHODS: The properties of GLP-2(3-33), a GLP-2(1-33) metabolite, were determined in baby-hamster kidney cells transfected with the mouse GLP-2 receptor complementary DNA and in isolated murine intestinal muscle strips. To investigate the role of endogenous GLP-2(1-33) in gut adaptation, GLP-2(3-33) was administered to mice that were re-fed for 24 hours after 24 hours of fasting, and the small intestine was analyzed. GLP-2(3-33) also was injected into rats for analysis of circulating GLP-2(1-33) levels. RESULTS: GLP-2(3-33) antagonized the actions of GLP-2(1-33) in vitro and ex vivo. Fasting mice exhibited small intestinal atrophy (37% +/- 1% decrease in small intestinal weight, 19% +/- 2% decrease in crypt-villus height, and 99% +/- 35% increase in villus apoptosis, P < .05-.01). Adaptive growth in re-fed mice restored all these parameters, as well as crypt-cell proliferation, to normal control levels (P < .05 vs. fasting); these adaptive changes were prevented partially or completely by co-administration of GLP-2(3-33) to refeeding mice (by 32% +/- 19% to 103% +/- 15%, P < .05-.01 vs re-fed mice). Exogenous GLP-2(3-33) did not affect endogenous GLP-2(1-33) levels. CONCLUSIONS: These data show that endogenous GLP-2 regulates the intestinotropic response in re-fed mice through modulation of crypt-cell proliferation and villus apoptosis. GLP-2 is therefore a physiologic regulator of the dynamic adaptation of the gut mucosal epithelium in response to luminal nutrients.     

Meta-analysis of head-to-head clinical trials comparing incretin-based glucose-lowering medications and basal insulin: An update including recently developed glucagon-like peptide-1 (GLP-1) receptor agonists and the glucose-dependent insulinotropic polypeptide/GLP-1 receptor co-agonist tirzepatide

Objective

To assess comparative efficacy, safety and tolerability of injectable incretin-based glucose-lowering medications (IBGLMs) versus basal insulin treatment in patients with type 2 diabetes.

Research Design and Methods

We performed an updated meta-analysis of randomized clinical trials of head-to-head comparisons of IBGLMs (short- and long-acting glucagon-like peptide-1 [GLP-1] receptor agonists [GLP-1RAs] and glucose-dependent insulinotropic polypeptide [GIP]/GLP-1 receptor co-agonist tirzepatide) versus basal insulin using a PubMed database search (April 2022). The primary endpoint was difference in reduction of glycated haemoglobin (HbA_1c) versus baseline between pooled IBGLMs (fixed-effects meta-analysis) and their subgroups (random-effects meta-analysis) versus basal insulin treatment (mean differences). Secondary endpoints were fasting plasma glucose, body weight, HbA_1c target achievement, hypoglycaemia, blood pressure and lipids. Risk of bias assessment was performed using Jadad scores and the Risk of Bias tool 2.0.

Results

In all, 20 studies, representing 47 study arms and 11 843 patients, were eligible. Compared with basal insulin, IGBLMs lowered HbA_1c by 0.48 (0.45-0.52)% more than did basal insulin treatment. This effect was driven by pooled long-acting GLP-1RAs (ΔHbA_1c −0.25 [−0.38; −0.11]%) and the only GIP/GLP-1 receptor co-agonist, tirzepatide (pooled doses; ΔHbA_1c −0.90 [−1.06; −0.75]%), while short-acting GLP-1RAs were equally effective compared with basal insulin (P = 0.90). All IBGLM subgroups achieved significantly lower body weight versus insulin treatment (−4.6 [−4.7; −4.4] kg), in particular tirzepatide (−12.0 [−13.8; −10.1] kg). IBGLMs significantly reduced hypoglycaemia and blood pressure and improved lipid variables. Risk of bias was low. IBGLM treatment was associated with more nausea, vomiting and diarrhoea and study medication discontinuation.

Conclusions

Recently introduced, highly effective IBGLMs were superior to basal insulin treatment, reinforcing the recommendation that IBGLMs should be considered as the first injectable treatment for most patients with type 2 diabetes.     

Role of AMPK in pancreatic beta cell function

Pharmacological activation of AMP activated kinase (AMPK) by metformin has proven to be a beneficial therapeutic approach for the treatment of type II diabetes. Despite improved glucose regulation achieved by administration of small molecule activators of AMPK, the potential negative impact of enhanced AMPK activity on insulin secretion by the pancreatic beta cell is an important consideration. In this review, we discuss our current understanding of the role of AMPK in central functions of the pancreatic beta cell, including glucose-stimulated insulin secretion (GSIS), proliferation, and survival. In addition we discuss the controversy surrounding the role of AMPK in insulin secretion, underscoring the merits and caveats of methods used to date.     

Reproductive actions of prolactin mediated through short and long receptor isoforms

Prolactin (PRL) is a polypeptide hormone with a wide range of physiological functions, and is critical for female reproduction. PRL exerts its action by binding to membrane bound receptor isoforms broadly classified as the long form and the short form receptors. Both receptor isoforms are highly expressed in the ovary as well as in the uterus. Although signaling through the long form is believed to be more predominant, it remains unclear whether activation of this isoform alone is sufficient to support reproductive functions or whether both types of receptor are required. The generation of transgenic mice selectively expressing either the short or the long form of PRL receptor has provided insight into the differential signaling mechanisms and physiological functions of these receptors. This review describes the essential finding that both long and short receptor isoforms are crucial for ovarian functions and female fertility, and highlights novel mechanisms of action for these receptors.     

慢性低氧对肺动脉高压大鼠肺血管ERK 1/2、p38MAPK表达的影响

目的：通过建立慢性低氧性肺动脉高压大鼠模型,研究慢性低氧对大鼠肺血管细胞外信号调节蛋白激酶(ERK1/2)、p38MAPK蛋白表达的影响。方法建立慢性常压低氧肺动脉高压大鼠模型,将雄性SD大鼠随机分为正常对照组、低氧1d、3d、7d、14d和21d组,应用免疫组织化学技术检测肺动脉高压形成过程中大鼠肺血管 ERK1/2、p38MAPK 蛋白表达水平。结果①RVSP 和 RV/(LV+S)比值较正常对照组明显增加(P<0.05),低氧后3 d、7 d、14 d和21 d后大鼠肺血管明显增厚;②ERK1/2、p38MAPK蛋白广泛分布于肺血管内皮细胞、平滑肌细胞和成纤维细胞中,且随着低氧时间的延长,ERK1/2、p38MAPK蛋白表达量增加。结论 ERK1/2、p38MAPK 蛋白表达量的上调可能参与了慢性低氧诱导的大鼠肺动脉高压肺血管重塑的发生、发展过程。     

The activation of p38alpha, and not p38beta, mitogen-activated protein kinase is required for ischemic preconditioning

Numerous studies show that pharmacological inhibition of p38 mitogen-activated protein kinases (p38s) before lethal ischemia prevents conditioning. However, these inhibitors have off-target effects and do not discriminate between the alpha and beta isoforms; the activation of which is thought to have diverse and perhaps opposing actions with p38α aggravating, and p38β reducing, myocardial injury. We adopted a chemical genetic approach using mice in which either the p38α (DRα) or p38β (DRβ) alleles were targeted to substitute the “gatekeeper” threonine residue for methionine, thereby preventing the binding of a pharmacological inhibitor, SB203580. Isolated, perfused wild-type (WT), DRα and DRβ mouse hearts underwent ischemic preconditioning with 4 cycles of 4 min ischemia/6 min reperfusion, with or without SB203580 (10 µM), followed by 30 min of global ischemia and 120 min of reperfusion. In WT and DRβ hearts, SB203580 completely abolished the reduction in myocardial infarction seen with preconditioning and also the phosphorylation of downstream substrates of p38. These effects of SB203580 were not seen in DRα hearts. Furthermore ischemic preconditioning occurred unaltered in p38β null hearts. Contrary to expectation the activation of p38α, and not p38β, is necessary for ischemic preconditioning. Since p38α is also the isoform that leads to lethal myocardial injury, it is unlikely that targeted therapeutic strategies to achieve isoform-selective inhibition will only prevent the harmful consequences of activation.     

Glucagon-like peptide-1 and its receptor agonist exendin-4 modulate cholangiocyte adaptive response to cholestasis

BACKGROUND & AIMS: Cholangiopathies are characterized by progressive dysregulation of the balance between proliferation and death of cholangiocytes. In the course of cholestasis, cholangiocytes undergo a neuroendocrine transdifferentiation and their biology is regulated by neuroendocrine hormones. Glucagon-like peptide-1 (GLP-1), secreted by neuroendocrine cells, sustains beta-cell survival in experimental diabetes and induces the neuroendocrine transdifferentiation of pancreatic ductal cells. GLP-1 receptor (GLP-1R) selective agonist exendin-4 is used in humans as a novel therapeutic tool for diabetes. The aim of this study was to define if GLP-1 modulates cholangiocyte biologic response to cholestasis. METHODS: Expression of GLP-1R in cholangiocytes was determined. Effects on cholangiocyte proliferation of the in vitro and in vivo exposure to GLP-1 or exendin-4, together with the intracellular signals, were then studied. Synthesis of GLP-1 by cholangiocytes and the effects of GLP-1R blockage on their growth were also determined. RESULTS: Cholangiocytes express the GLP-1 receptor, which is up-regulated in the course of cholestasis. GLP-1 and exendin-4 increase cholangiocyte growth both in vitro and in vivo. The GLP-1R signal is mediated by the phosphatidyl-inositol-3-kinase, cAMP/Protein Kinase A, and Ca(2+)-CamKIIalpha but not by the ERK1/2 and PKCalpha pathways. Proliferating cholangiocytes synthesize GLP-1: neutralization of its action by GLP-1R antagonist blunts cholangiocyte response to cholestasis. CONCLUSIONS: GLP-1 is required for the cholangiocyte adaptive response to cholestasis. Cholangiocytes are susceptible to the activation of GLP-1R and respond with increased proliferation and functional activity. Exendin-4 availability for employment in humans and these data may open novel perspectives for the medical treatment of cholangiopathies.     

Stimulatory effect of insulin on theca-interstitial cell proliferation and cell cycle regulatory proteins through MTORC1 dependent pathway

The present study examined the effect of insulin-mediated activation of the mammalian target of rapamycin complex 1 (MTORC1) signaling network on the proliferation of primary culture of theca-interstitial (T-I) cells. Our results show that insulin treatment increased proliferation of the T-I cells through the MTORC1-dependent signaling pathway by increasing cell cycle regulatory proteins. Inhibition of ERK1/2 signaling caused partial reduction of insulin-induced phosphorylation of RPS6KB1 and RPS6 whereas inhibition of PI3-kinase signaling completely blocked the insulin response. Pharmacological inhibition of MTORC1 with rapamycin abrogated the insulin-induced phosphorylation of EIF4EBP1, RPS6KB1 and its downstream effector, RPS6. These results were further confirmed by demonstrating that knockdown of Mtor using siRNA reduced the insulin-stimulated MTORC1 signaling. Furthermore, insulin-stimulated T-I cell proliferation and the expression of cell cycle regulatory proteins CDK4, CCND3 and PCNA were also blocked by rapamycin. Taken together, the present studies show that insulin stimulates cell proliferation and cell cycle regulatory proteins in T-I cells via activation of the MTORC1 signaling pathway.     

Biology of incretins: GLP-1 and GIP

This review focuses on the mechanisms regulating the synthesis, secretion, biological actions, and therapeutic relevance of the incretin peptides glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1). The published literature was reviewed, with emphasis on recent advances in our understanding of the biology of GIP and GLP-1. GIP and GLP-1 are both secreted within minutes of nutrient ingestion and facilitate the rapid disposal of ingested nutrients. Both peptides share common actions on islet beta-cells acting through structurally distinct yet related receptors. Incretin-receptor activation leads to glucose-dependent insulin secretion, induction of beta-cell proliferation, and enhanced resistance to apoptosis. GIP also promotes energy storage via direct actions on adipose tissue, and enhances bone formation via stimulation of osteoblast proliferation and inhibition of apoptosis. In contrast, GLP-1 exerts glucoregulatory actions via slowing of gastric emptying and glucose-dependent inhibition of glucagon secretion. GLP-1 also promotes satiety and sustained GLP-1-receptor activation is associated with weight loss in both preclinical and clinical studies. The rapid degradation of both GIP and GLP-1 by the enzyme dipeptidyl peptidase-4 has led to the development of degradation-resistant GLP-1-receptor agonists and dipeptidyl peptidase-4 inhibitors for the treatment of type 2 diabetes. These agents decrease hemoglobin A1c (HbA1c) safely without weight gain in subjects with type 2 diabetes. GLP-1 and GIP integrate nutrient-derived signals to control food intake, energy absorption, and assimilation. Recently approved therapeutic agents based on potentiation of incretin action provide new physiologically based approaches for the treatment of type 2 diabetes.     

Down-regulation of the dual-specificity phosphatase MKP-1 suppresses tumorigenicity of pancreatic cancer cells

BACKGROUND & AIMS: In both pancreatic cancer and chronic pancreatitis, there is enhanced expression of mitogenic growth factors and their tyrosine kinase receptors, which have the capacity to activate mitogen-activated protein kinase (MAPK). In view of the important role of MAPK kinase phosphatase (MKP)-1 in the regulation of MAPK activation, the expression and functional role of MKP-1 was analyzed. METHODS: Pancreatic tissues were analyzed by Northern blotting, Western blotting, and immunohistochemistry. Pancreatic cancer cells were transfected with a full-length MKP-1 antisense construct. Growth characteristics and tumorigenicity in vivo and the effects of mitogenic growth factors on cell growth and MAPK activation were determined in transfected and control cells. RESULTS: MKP-1 messenger RNA (mRNA) levels were increased in pancreatic cancer and chronic pancreatitis (CP) tissues. Moderate to strong MKP-1 immunoreactivity was present in the cancer cells, ductal cells of pancreatic intraepithelial neoplasia, and in tubular complexes in CP. Down-regulation of MKP-1 resulted in decreased anchorage-dependent and -independent growth of pancreatic cancer cells, and decreased tumorigenicity in a nude mouse tumor model. MKP-1 down-regulation led to decreased proliferation and sustained MAPK activation in response to mitogens. CONCLUSIONS: Suppression of MKP-1 expression reduces the tumorigenicity of pancreatic cancer cells in vivo, suggesting that MKP-1 contributes to enhanced mitogenic signaling in pancreatic cancer cells.     

Role of mammalian sirtuin 1 (SIRT1) in lipids metabolism and cell proliferation of goose primary hepatocytes

Our result showed in the fatty liver formation induced-by overfeeding goose, it was accompanied by an activation of mammalian target of rapamycin (mTOR) pathway and cell proliferation. Recent studies have suggested a crucial role for mammalian sirtuin 1 (SIRT1) in regulating lipid metabolism and cell proliferation, so we hypothesize that resveratrol -activated and nicotinamide -inhibited SIRT1 acts goose hepatocellular lipid metabolism and cell proliferation by mTOR signal pathway. Here we show that both resveratrol and nicotinamide could evidently affect the DNA synthesis rate, the lipids accumulation, the mRNA level and protein content of genes involved in the lipids metabolism, mTOR signal pathway, and the cell cycle progression of goose primary hepatocytes. Moreover, rapamycin decreased the effect of nicotinamide on lipids accumulation and cell proliferation. These findings suggest that SIRT1 functions as a regulator for mTOR signaling and plays an essential role in the regulation of hepatocyte lipid metabolism and cell proliferation.