Therapeutic effects of the allosteric protein tyrosine phosphatase 1B inhibitor KY-226 on experimental diabetes and obesity via enhancements in insulin and leptin signaling in mice

Phosphoproteomic investigation of targets of protein phosphatases in EGFR signaling

Receptor tyrosine kinases (RTKs) initiate cellular signaling pathways, which are regulated through a delicate balance of phosphorylation and dephosphorylation events. While many studies of RTKs have focused on downstream-activated kinases catalyzing the site-specific phosphorylation, few studies have focused on the phosphatases carrying out the dephosphorylation. In this study, we analyzed six protein phosphatase networks using chemical inhibitors in context of epidermal growth factor receptor (EGFR) signaling by mass spectrometry-based phosphoproteomics. Specifically, we focused on protein phosphatase 2C (PP2C), involved in attenuating p38-dependent signaling pathways in various cellular responses, and confirmed its effect in regulating p38 activity in EGFR signaling. Furthermore, utilizing a p38 inhibitor, we classified phosphosites whose phosphorylation status depends on PP2C inhibition into p38-dependent and p38-independent sites. This study provides a large-scale dataset of phosphatase-regulation of EGF-responsive phosphorylation sites, which serves as a useful resource to deepen our understanding of EGFR signaling.

A PTP1B-Cdk3 Signaling Axis Promotes Cell Cycle Progression of Human Glioblastoma Cells through an Rb-E2F Dependent Pathway

PTP1B plays a key role in developing different types of cancer. However, the molecular mechanism underlying this effect is unclear. To identify molecular targets of PTP1B that mediate its role in tumorigenesis, we undertook a SILAC-based phosphoproteomic approach, which allowed us to identify Cdk3 as a novel PTP1B substrate. Substrate trapping experiments and docking studies revealed stable interactions between the PTP1B catalytic domain and Cdk3. In addition, we observed that PTP1B dephosphorylates Cdk3 at tyrosine residue 15 in vitro and interacts with it in human glioblastoma cells. Next, we found that pharmacological inhibition of PTP1B or its depletion with siRNA leads to cell cycle arrest with diminished activity of Cdk3, hypophosphorylation of Rb, and the downregulation of E2F target genes Cdk1, Cyclin A, and Cyclin E1. Finally, we observed that the expression of a constitutively active Cdk3 mutant bypasses the requirement of PTP1B for cell cycle progression and expression of E2F target genes. These data delineate a novel signaling pathway from PTP1B to Cdk3 required for efficient cell cycle progression in an Rb-E2F dependent manner in human GB cells.

Targeting protein modifications in metabolic diseases: molecular mechanisms and targeted therapies

The ever-increasing prevalence of noncommunicable diseases (NCDs) represents a major public health burden worldwide. The most common form of NCD is metabolic diseases, which affect people of all ages and usually manifest their pathobiology through life-threatening cardiovascular complications. A comprehensive understanding of the pathobiology of metabolic diseases will generate novel targets for improved therapies across the common metabolic spectrum. Protein posttranslational modification (PTM) is an important term that refers to biochemical modification of specific amino acid residues in target proteins, which immensely increases the functional diversity of the proteome. The range of PTMs includes phosphorylation, acetylation, methylation, ubiquitination, SUMOylation, neddylation, glycosylation, palmitoylation, myristoylation, prenylation, cholesterylation, glutathionylation, S-nitrosylation, sulfhydration, citrullination, ADP ribosylation, and several novel PTMs. Here, we offer a comprehensive review of PTMs and their roles in common metabolic diseases and pathological consequences, including diabetes, obesity, fatty liver diseases, hyperlipidemia, and atherosclerosis. Building upon this framework, we afford a through description of proteins and pathways involved in metabolic diseases by focusing on PTM-based protein modifications, showcase the pharmaceutical intervention of PTMs in preclinical studies and clinical trials, and offer future perspectives. Fundamental research defining the mechanisms whereby PTMs of proteins regulate metabolic diseases will open new avenues for therapeutic intervention.

Discovery and evaluation of biphenyl derivatives of 2-iminobenzimidazoles as prototype dual PTP1B inhibitors and AMPK activators with in vivo antidiabetic activity

This work describes the synthesis of series hydrobromides of N-(4-biphenyl)methyl-N'-dialkylaminoethyl-2-iminobenzimidazoles, which, due to the presence of two privileged structural fragments (benzimidazole and biphenyl moieties), can be considered as bi-privileged structures. Compound 7a proved to activate AMP-activated kinase (AMPK) and simultaneously inhibit protein tyrosine phosphatase 1B (PTP1B) with similar potency. This renders it an interesting prototype of potential antidiabetic agents with a dual-target mechanism of action. Using prove of concept in vivo study, we show that dual-targeting compound 7a has a disease-modifying effect in a rat model of type 2 diabetes mellitus via improving insulin sensitivity and lipid metabolism.

Status of research on natural protein tyrosine phosphatase 1B inhibitors as potential antidiabetic agents: Update

Protein tyrosine phosphatase 1B (PTP1B) is a crucial therapeutic target for multiple human diseases comprising type 2 diabetes (T2DM) and obesity because it is a seminal part of a negative regulator in both insulin and leptin signaling pathways. PTP1B inhibitors increase insulin receptor sensitivity and have the ability to cure insulin resistance-related diseases. However, the few PTP1B inhibitors that entered the clinic (Ertiprotafib, ISIS-113715, Trodusquemine, and JTT-551) were discontinued due to side effects or low selectivity. Molecules with broad chemical diversity extracted from natural products have been reported to be potent PTP1B inhibitors with few side effects. This article summarizes the recent PTP1B inhibitors extracted from natural products, clarifying the current research progress, and providing new options for designing new and effective PTP1B inhibitors.

Drug-Repurposing Screening Identified Tropifexor as a SARS-CoV-2 Papain-like Protease Inhibitor

The global COVID-19 pandemic underscores the dire need for effective antivirals. Encouraging progress has been made in developing small-molecule inhibitors targeting the SARS-CoV-2 RNA-dependent RNA polymerase (RdRp) and main protease (Mpro). However, the development of papain-like protease (PLpro) inhibitors faces several obstacles. Nevertheless, PLpro represents a high-profile drug target given its multifaceted roles in viral replication. PLpro is involved in not only the cleavage of viral polyprotein but also the modulation of host immune response. In this study, we conducted a drug-repurposing screening of PLpro against the MedChemExpress bioactive compound library and identified three hits, EACC, KY-226, and tropifexor, as potent PLpro inhibitors with IC50 values ranging from 3.39 to 8.28 μM. The three hits showed dose-dependent binding to PLpro in the thermal shift assay. In addition, tropifexor inhibited the cellular PLpro activity in the FlipGFP assay with an IC50 of 10.6 μM. Gratifyingly, tropifexor showed antiviral activity against SARS-CoV-2 in Calu-3 cells at noncytotoxic concentrations. Overall, tropifexor represents a novel PLpro inhibitor that can be further developed as SARS-CoV-2 antivirals.

Obesity as a Risk Factor for Dementia and Alzheimer's Disease: The Role of Leptin

Obesity is a growing worldwide health problem, affecting many people due to excessive saturated fat consumption, lack of exercise, or a sedentary lifestyle. Leptin is an adipokine secreted by adipose tissue that increases in obesity and has central actions not only at the hypothalamic level but also in other regions and nuclei of the central nervous system (CNS) such as the cerebral cortex and hippocampus. These regions express the long form of leptin receptor LepRb, which is the unique leptin receptor capable of transmitting complete leptin signaling, and are the first regions to be affected by chronic neurocognitive deficits, such as mild cognitive impairment (MCI) and Alzheimer's Disease (AD). In this review, we discuss different leptin resistance mechanisms that could be implicated in increasing the risk of developing AD, as leptin resistance is frequently associated with obesity, which is a chronic low-grade inflammatory state, and obesity is considered a risk factor for AD. Key players of leptin resistance are SOCS3, PTP1B, and TCPTP whose signalling is related to inflammation and could be worsened in AD. However, some data are controversial, and it is necessary to further investigate the underlying mechanisms of the AD-causing pathological processes and how altered leptin signalling affects such processes.

Anti-obesity and Anti-diabetic Effect of Ursolic Acid against Streptozotocin/High Fat Induced Obese in Diabetic Rats

Obesity is occurring due to continue taken high fat diet; this is the fast-growing problem reaching epidemic proportion globally. Ursolic acid altered the abnormal glucose metabolism in diabetic rats. In this experimental protocol, we examine ursolic acid (UA) anti-obesity effect against streptozotocin (STZ) and high-fat diet-induced obesity in rats. Orally administered the ursolic acid (2.5, 5 and 10 mg/kg) dose to the hyperglycemic rats for 8 weeks and estimated the blood glucose level at different time intervals. Biochemical, hepatic, lipid, renal and antioxidant parameters were estimated. Traf-4, Mapk-8, Traf-6 and genes such as Ins-1, ngn-3 and Pdx-1 mRNA expression were estimated using qRT-PCR to scrutinize the molecular mechanism in MAPK downstream JNK cascade and insulin pathway signalling pathways. Ursolic acid significantly (p<0.001) down-regulated the blood glucose level at dose dependent manner. Its also reduced the plasma insulin level, non-essential fatty acid and increased the level of adiponectin as compared to obese control group rats. Ursolic acid treated group rats reduced the level of total cholesterol and triglycerides. Ursolic-acid-treated rats have been shown to decrease oxidative stress in pancreatic tissue by restoring the free radical effect of scavenging, suppress the Traf-6, Mapk-8 and Traf-4 mRNA expression, enhance the expression of Pdx-1, Ins-1 and Ngn-3 and ensure the regeneration of pancreas β cells and therefore pancreas insulin. The current result suggested the anti-obese effect of ursolic acid against high fat diet (HFD) induced obese rats via alteration of insulin and JNK signaling pathway.

Aldose reductase and protein tyrosine phosphatase 1B inhibitors as a promising therapeutic approach for diabetes mellitus

Diabetes mellitus is a metabolic disease characterized by high blood glucose levels and usually associated with several chronic pathologies. Aldose reductase and protein tyrosine phosphatase 1B enzymes have identified as two novel molecular targets associated with the onset and progression of type II diabetes and related comorbidities. Although many inhibitors against these enzymes have already found in the field of diabetic mellitus, the research for discovering more effective and selective agents with optimal pharmacokinetic properties continues. In addition, dual inhibition of these target proteins has proved as a promising therapeutic approach. A variety of diverse scaffolds are presented in this review for the future design of potent and selective inhibitors of aldose reductase and protein tyrosine phosphatase 1B based on the most important structural features of both enzymes. The discovery of novel dual aldose reductase and protein tyrosine phosphatase 1B inhibitors could be effective therapeutic molecules for the treatment of insulin-resistant type II diabetes mellitus. The methods used comprise a literature survey and X-ray crystal structures derived from Protein Databank (PDB). Despite the available therapeutic options for type II diabetes mellitus, the inhibitors of aldose reductase and protein tyrosine phosphatase 1B could be two promising approaches for the effective treatment of hyperglycemia and diabetes-associated pathologies. Due to the poor pharmacokinetic profile and low in vivo efficacy of existing inhibitors of both targets, the research turned to more selective and cell-permeable agents as well as multi-target molecules.

Effect of Caesalpinia bonduc Polyphenol Extract on Alloxan-Induced Diabetic Rats in Attenuating Hyperglycemia by Upregulating Insulin Secretion and Inhibiting JNK Signaling Pathway

Caesalpinia bonduc has been used in herbal medicines for the treatment of a wide range of diseases from decades. The present study has explored the remedial potential and underlying mechanism of polyphenol extract of Caesalpinia bonduc in alloxanized diabetic rats. HPLC/MS analysis confirmed the presence of phenolics in considerable concentrations in Caesalpinia bonduc extract. Administration of different doses (250 and 500 mg/kg) of CPP extract to hyperglycemic rats for 8 weeks restored blood and serum glucose, insulin, glycosylated hemoglobin, leptin, amylin, and carbohydrate metabolizing enzymes level towards normal compared to alloxanized diabetic group. The effect of CPP extract on various genes such as Pdx-1, Ins-1, ngn-3, GLUT-4, and IRS-1 in insulin signaling pathway and Traf-4, Traf-6, and Mapk-8 in MAPK downstream JNK cascade was examined through qRT-PCR to access the core molecular mechanism involved in CPP-induced recovery of diabetes. Results have revealed that CPP extract reduced oxidative stress in pancreatic β cells by restoring free radical scavenging potential, reducing the mRNA expression of Mapk-8, Traf-4, and Traf-6, and increasing the Pdx-1, Ins-1, ngn-3, GLUT-4, and IRS-1 expression ensuing regeneration of β cells and subsequent insulin release from pancreas. The results obtained in this study recommend that CPP extract may be a promising therapeutic restorative agent in the treatment of diabetes mellitus.

KY-226 Protects Blood-brain Barrier Function Through the Akt/FoxO1 Signaling Pathway in Brain Ischemia

KY-226 is a protein tyrosine phosphatase 1B (PTP1B) inhibitor that protects neurons from cerebral ischemic injury. KY-226 restores Akt (protein kinase B) phosphorylation and extracellular signal-regulated kinase (ERK) reduction in transient middle cerebral artery occlusion (tMCAO) damage. However, the mechanisms underlying the neuroprotective effects of KY-226 are unclear. To address this, the effects of KY-226 on blood-brain barrier (BBB) dysfunction were examined in tMCAO mice. KY-226 (10 mg/kg, i.p.) was administered to ICR mice 30 min after 2 h of tMCAO. To assess Akt or ERK involvement, wortmannin (i.c.v.) or U0126 (i.v.), selective inhibitors of PI3K and ERK, respectively, were administered to mice 30 min before ischemia. BBB integrity was assessed by Evans blue leakage 24 h post-reperfusion. The levels of tight junction (TJ) proteins, ZO-1 and occludin, were measured by western blotting; ZO-1 mRNA level was measured by RT-PCR. Compared to vehicle, KY-226 treatment prevented BBB breakdown and reduction in TJ protein levels. KY-226 treatment restored ZO-1 mRNA levels post-reperfusion. Pre-administration of wortmannin or U0126 blocked the protective effects of KY-226 on ZO-1 protein and mRNA reduction in tMCAO mice. In bEnd.3 cells, lipopolysaccharide treatment reduced mRNA and protein levels of ZO-1, an effect rescued by KY-226 treatment. Further, KY-226 treatment restored phosphorylation of pAkt (T308) and its downstream target forkhead box protein O1 (FoxO1) (S256) in bEnd.3 cells. Collectively, we demonstrate that KY-226 protects BBB integrity by restoration of TJ proteins, an effect partly mediated by Akt/FoxO1 pathway activation. Thus, protection of BBB integrity likely underlies KY-226-induced neuroprotection in tMCAO mice.

C-terminal site-specific PEGylated Exendin-4 analog: A long-acting glucagon like Peptide-1 receptor agonist, on glycemic control and beta cell function in diabetic db/db mice

PEG modification is a common clinical strategy for prolonging the half-life of therapeutic proteins or polypeptides. In a previous work, we have successfully synthesized PEG-modified Exendin-4 (PE) by conjugating a 20 kDa PEG to the C-terminal of Exendin-4. Then, we introduced an integrative characterization for PE to evaluate its hypoglycemic activity and pharmacokinetic properties. The normoglycemic efficacies and therapeutic activity of PE were investigated in db/db mice. The hypoglycemic time after single administration of PE on db/db mice was prolonged from 8.4 h to 54.9 h. In multiple treatment with PE, the fasting blood glucose in various PE dosages (50, 150, and 250 nmol/kg) were remarkably reduced, and the glycosylated hemoglobin level was decreased to 2.0%. When the in vivo single- and multiple-dose pharmacokinetics of PE were examined in Sprague-Dawley rats, the half-life was prolonged to 31.7 h, and no accumulation effect was observed. Overall, this study provided a novel promising therapeutic approach to improving glucose-controlling ability and extending half-life without accumulation in vivo for long-acting treatment of type-2 diabetes.